Physiology

The testis can be thought of as having two major interconnected functions in the adult: the production of testosterone, which maintains a wide range of physiological processes; and the production of spermatozoa and thereby fertility.

Spermatogenesis

Spermatogenesis takes place in several hundred tightly coiled seminiferous tubules arranged in lobules (Figure 21.1) (Dym 1977), which constitute some 80% of testicular volume in man. Testis volume therefore reflects spermatogenesis more than testosterone production. Each tubule resembles a loop draining at both ends into a network of tubules, the rete testis, and thence into the epididymis, a single but highly coiled tube which, in turn, drains into the unconvoluted and muscular-walled vas deferens.

Figure 21.1 Human testis, epididymis and vas deferens showing efferent ducts leading from the rete testis to the caput epididymis and the cauda epididymis, continuing to become the vas deferens.

From Dym M (1977). In Histology pp. 981 eds L Weiss and RO Greep, with permission of Elsevier.

The walls of the seminiferous tubules are composed of germ cells and Sertoli cells around a central lumen, surrounded by peritubular myoid cells and a basement membrane (Figure 21.2). Spermatogenesis is a continuous sequence of closely regulated events, highly organized in space and time, whereby cohorts of undifferentiated diploid germ cells (spermatogonia) multiply and, while maintaining the population of stem cell spermatogonia, are then transformed into haploid spermatozoa. The following events can be observed in the seminiferous epithelium during normal spermatogenesis.

• Mitotic division (at least four) of stem cells to form cohorts of spermatogonia which, at intervals of 16 days, differentiate into primary preleptotene spermatocytes to initiate meiosis.

• Meiotic reduction divisions of spermatocytes to form round spermatids.

• Continuous remodelling of Sertoli cells in order to direct the migration of germ cells from basal to luminal positions.

• Transformation (spermiogenesis) of large spherical spermatids into compact, virtually cytoplasm-free spermatozoa with condensed DNA in the head crowned by an apical acrosomal cap, and a tail capable of propulsive beating movements.

• Spermiation, whereby the spermatozoa are released from the Sertoli cell cytoplasm into the tubular lumen.

Figure 21.2 Diagrammatic representation of the anatomical and functional relationship between germ cells, Sertoli cells and Leydig cells. Note the division of the seminiferous epithelium into adluminal and basal compartments by the tight junctions between adjacent Sertoli cells and the bidirectional secretion of Sertoli cell products (e.g. inhibin) into the lumen and interstitial space. ABP-T, androgen-binding protein testosterone; FSH, follicle-stimulating hormone; LH, luteinizing hormone; T, testosterone.

Cohorts of undifferentiated germ cells, joined to each other by cytoplasmic bridges, progress through these different steps in synchrony so that several generations of developing germ cells are usually observed at any one part of the seminiferous epithelium at any one time. The total time taken for a cohort of spermatogonia to develop into spermatozoa is 74 days, during which time at least three further generations of spermatogonia have also successively, at intervals of 16 days, initiated their development. In the human, spermatogenesis is arranged in a helical manner, so that cross-sections show more than one stage of spermatogenesis within individual seminiferous tubules. This organizational arrangement differs from that in many other species (e.g. rodents), in which spermatogenesis is arranged longitudinally and thus only one stage of spermatogenesis is seen in a cross-section of a tubule.

Hypothalamic–pituitary–testicular axis

The secretion of gonadotrophins from the anterior pituitary gland is controlled by gonadotrophin-releasing hormone (GnRH) released into the pituitary portal circulation from axon terminals in the hypothalamic median eminence. These neurosecretory neurones in the medial basal hypothalamus are responsive to a wide variety of sensory inputs as well as to gonadal negative feedback. GnRH stimulates the secretion of both LH and FSH. In the adult male, GnRH is released episodically into the pituitary portal circulation at a frequency of approximately every 140 min; each volley of GnRH elicits an immediate release of LH, producing the typical pulsatile pattern of LH in the systemic circulation (Figure 21.3; Wu et al 1989). Although also secreted episodically, FSH and testosterone pulses are not apparent in normal men because of the slower secretion of newly synthesized rather than stored hormone and the longer circulating half-lives. The intermittent mode of GnRH stimulation, within a narrow physiological range of frequency, is obligatory for sustaining the normal pattern of gonadotrophin secretion. Continuous or high-frequency GnRH stimulation paradoxically desensitizes the pituitary gonadotrophin response in men as in women, because of depletion of receptors and refractoriness of postreceptor response mechanisms. It has recently been demonstrated that the secretion of GnRH is dependent on the newly-described kisspeptin (also known as ‘metastin’). Mutations of the kisspeptin receptor result in pubertal failure. Kisspeptin-containing neurones impinge directly on GnRH neurones in the hypothalamus, and there is emerging evidence that they also mediate effects of metabolic signals such as leptin on the reproductive axis (Seminara and Crowley 2008).

Figure 21.3 (A) Functional relationships in the hypothalamic–pituitary–testicular axis. Gonadotrophin-releasing hormone (GnRH) is secreted into the hypophyseal circulation in an episodic manner, represented by a luteinizing hormone (LH) pulse in the peripheral circulation. (B) Peripheral blood LH concentration sampled in an adult male at 10-min intervals for 24 h from 0900 to 0900 h.

Testosterone exerts the major negative feedback action on gonadotrophin secretion. Its effect is predominantly to restrict the frequency of GnRH pulses from the hypothalamus to within the physiological range. Testosterone also acts on the pituitary to reduce the amplitude of the LH response to GnRH. It is now recognized that these inhibitory effects on GnRH and gonadotrophin secretion are, in part, mediated following conversion of testosterone to oestradiol by the enzyme P450 aromatase. This is demonstrated both by administration of aromatase inhibitors to normal men and by the finding that men with either mutant, non-functional oestrogen receptors or absent aromatase activity have markedly elevated gonadotrophin concentrations despite high-normal testosterone concentrations (Smith et al 1994, Morishima et al 1995). Interestingly, these men also showed marked osteoporosis, suggesting a distinct role for oestrogen in bone. Feedback inhibition of pituitary FSH synthesis is predominantly mediated by inhibin B and also by testosterone, particularly at high concentrations. The regulation of FSH secretion by inhibin in addition to testosterone results in the selective rise in FSH but not LH concentrations in men with various disorders of spermatogenesis.

The spermatozoon

The primary function of the spermatozoon is the delivery of a male pronucleus to the fertilized egg. The spermatozoon must conserve its DNA and transport it to the site of fertilization, where it must recognize and fuse with a receptive egg. The ejaculated spermatozoon must first escape from the seminal plasma in which it is deposited beside the cervix, and penetrate the barrier presented by cervical mucus. It must then travel through the uterus to the site of fertilization in the fallopian tube. During this journey, it must complete the process of functional maturation known as ‘capacitation’, an ordered series of events involving reorganization of cell surface components and changes in cellular metabolism and motility patterns, which are a prerequisite for successful fertilization. Having reached the oviduct, the male gamete must recognize the oocyte, penetrate the cumulus oophorus and bind to the zona pellucida. At this point, it must display a unique pattern of movement known as ‘hyperactivated motility’ and undergo the acrosome reaction. This process is initiated by a specific protein component of the zona pellucida (ZP3) and results in release of the contents of the acrosomal matrix, which include the serine protease acrosin and other hydrolytic enzymes including hyaluronidase. In addition, the acrosome reaction results in the generation of a fusogenic equatorial segment, which is the zone of fusion with the oocyte plasma membrane. For a review of sperm structure and function, the reader is referred to Grudzinskas (1995).

To enable it to undertake these complex functions, the human spermatozoon has developed a highly specialized morphology, with its various structural components tailored to specific functional attributes. The appearance of the spermatozoon was first described over 300 years ago by Anthony van Leeuwenhoek. In outline, the spermatozoon has a dense oval head capped by an acrosome and is propelled by a motile tail (Figure 21.4; Fawcett 1975). The head is made up largely of highly condensed nuclear chromatin constituting the haploid chromosome complement, complexed with highly basic proteins termed ‘protamines’. It is covered in its anterior half by the acrosome, a membrane-enclosed sac of enzymes including acrosin and hyaluronidase. The area of the sperm head immediately behind the acrosome (the equatorial region) is important as it is this part which attaches to and fuses with the egg. The shape of the human sperm head is highly pleomorphic, making the morphological definition of a normal sperm head extremely challenging. Behind the head may be found a cytoplasmic droplet which consists of the remains of the residual cytoplasm left after the morphological remodelling of the cell during spermiogenesis.

Figure 21.4 The internal structure of a spermatozoon with the cell membrane removed.

From Fawcett DW, The mammalian spermatozoon. Dev Biol; 44: 394–436, 1975; with permission of Elsevier.

The tail of flagellum is usually further divided into the midpiece, principal piece and terminal piece, joined to the head by the connecting piece. The motor apparatus of the tail is the axoneme which consists of a central pair (doublets) of microtubules of non-contractile tubulin protein enclosed in a sheath linked radially to nine outer pairs of microtubules. The axonemal complex is surrounded by columns of outer dense fibres, which are, in turn, covered by a helix of mitochondria in the midpiece and a fibrous sheath in the principal piece. The dense fibres and the fibrous sheath form the cytoskeleton of the flagellum. Through the hydrolysis of adenosine triphosphate, the dynein arms undergo a series of conformational changes resulting in adjacent doublets sliding over one another. Synchronized movement of groups of microtubules propagating waves of bending motions of the tail is the key to the various modes of coordinated sperm motility. Energy for sperm motility is provided by the sheath of mitochondria in the midpiece of the tail through a second messenger system, involving the calcium-mediated calmodulin-dependent conversion of adenosine triphosphate to cAMP and interaction with the adenosine triphosphatase of the dynein.

Sperm transport and maturation

Spermatozoa within the testis and male tract are quiescent and play little active role in their own transport along the tract. Moreover, they are functionally immature and the maturation process continues as they pass through the epididymis. Passage out of the seminiferous tubules and through the main testicular collecting duct, the rete testis, is due to the flow of secretions from Sertoli cells and rete epithelium and to the intrinsic smooth muscle contractions of the tubules. From the rete, the cells pass through the efferent ducts to the epididymis, a 3–4-m-long single coiled tube whose function is under androgen and neural (adrenergic) control. It is typically subdivided into a caput or head region, a middle body or corpus, and a distal tail or cauda region which leads into the proximal vas deferens. The epididymal epithelium actively reabsorbs testicular fluid but also secretes a hyperosmolar fluid rich in glycerophosphorylcholine inositol and carnitine. The specific transport of these compounds across the epithelium creates a favourable fluid environment where progressive motility and fertilizing capacity of the spermatozoa are normally acquired. Some of these maturational changes are probably ‘housekeeping’ functions to ensure that the cell remains viable during its stay in the excurrent ducts, while others are associated with the development of fertilizing ability. In many animal species, spermatozoa retain fertility for several weeks in the cauda epididymis, which acts as a sperm reservoir prior to ejaculation. The human cauda epididymis, in contrast, has a relatively poor storage function, which diminishes further along the vas.

At ejaculation, spermatozoa pass along the vas and are mixed with the secretions of the accessory glands which form over 90% of the volume of the ejaculate. The seminal vesicles contribute the largest volume of alkaline fluid to the ejaculate, and are also the souce of seminal fructose, prostaglandins and coagulating proteins. Prostatic secretions contain proteolytic enzymes (which normally liquefy the coagulated proteins in semen within 20–30 min) and are rich in citric acid and zinc. Seminal plasma provides a support medium for transporting male gametes out of the body and for buffering the acidic pH of the vagina, so that a reservoir of functional sperm can be established after ejaculation. Just as testicular germ cells are subjected to constant attrition, ejaculated spermatozoa have to traverse the cervix, uterus and uterotubal junction before reaching the middle third of the oviduct, the site of fertilization. At each barrier, the sperm population is further reduced so that eventually only 200 or so of the most robust spermatozoa have the opportunity to fertilize the ovum. The number of functionally competent sperm is more important than the total number ejaculated.

The cervical canal is the first selective filtering barrier to meet the ejaculated sperm (Figure 21.5). This barrier is virtually complete except during midcycle, when oestrogenized cervical mucus glycoprotein fibrils form parallel chains called ‘micelles’ which permit spermatozoa with active progressive motility to swim through at a rate of 2–3 mm/min. Spermatozoa probably enter the uterine cavity from the internal os by virtue of their own motility, and appear in the uterine cavity approximately 90 min after insemination. The uterotubal junction is the second of the major physical barriers for spermatozoa. The mechanism for selectivity is not clear, but may depend on factors other than sperm motility since inert particles can pass through. Once the uterotubal junction has been successfully negotiated, a minority of sperm immediately traverse the oviduct to the ampulla; however, the majority congregate in the isthmus until ovulation has occurred. At this time, capacitated sperm showing hyperactivated movements of the tail gradually progress towards the fimbriated end, helped on by the muscular contraction of the oviduct wall and the flow of fluid in the oviduct. A maximum number of spermatozoa is present in the cervix 15–20 min following insemination and remains constant for 24 h, although a rapid decline has commenced by 48 h. Some spermatozoa may remain motile at the site of fertilization for up to 3 days (Mortimer 1995).

Figure 21.5 Attributes of sperm function associated with fertility in vivo. The spermatozoon must escape from seminal plasma, penetrate and traverse the cervical mucus barrier, reach the site of fertilization, undergo capacitation, bind to and penetrate the zona pellucida, fuse with the plasma membrane of the egg, and undergo nuclear decondensation within the cytoplasm of the oocyte.

Male reproductive ageing

Reproductive ageing in the male is not accompanied by such an overt and abrupt fall in gonadal function as occurs in women, but by a more gradual decline. These differences reflect the consequence of a finite pool of gametes compared with one that continually replicates from a stock of stem cells, and the clearer distinction between the endocrine and gametogenic functions of the gonads.

The decline in function of the endocrine output of the hypothalamo–pituitary–testicular axis with age is well established and results in a fall of approximately 50% in plasma testosterone concentrations (Vermeulen 1991). This has both central and peripheral components; thus, there is a relatively small increase in LH. The ‘andropause’ is increasingly the subject of investigation (Wu 2007), with large placebo-controlled studies of the effect of replacement under way. Changes in Sertoli cell function and spermatogenesis with ageing have received more limited investigation, but the data do suggest that there is indeed an age-related decline in function. Spermatogenesis, however, may be well maintained in elderly men.

Definition and epidemiology

Infertility is commonly defined as the failure of conception after at least 12 months of unprotected intercourse (Rowe 1993), but such a definition serves to obscure the true complexity of the clinical situation. In reality, those couples who fail to achieve a pregnancy within 12–24 months include those who can be considered sterile (i.e. who will never achieve a spontaneous pregnancy) and those who are more properly termed ‘subfertile’ and who have reduced fecundability (probability of achieving a pregnancy within one menstrual cycle) and hence a prolonged time to pregnancy. Accurate assessment of the prevalence of infertility has always been difficult because of the scarcity of large-scale, population-based studies. Estimates suggest that some 14–17% of couples may be affected at some time in their reproductive lives (Hull et al 1985), with European data suggesting that as many as one in four couples who try may experience difficulties in conceiving (Schmidt 2006).

While infertility is relatively common, it is very difficult indeed to establish the relative contribution of the male partner, given the profound difficulties which exist in the accurate diagnosis of male infertility. Most studies which have attempted to evaluate the aetiology of infertility have used the conventional criteria of semen quality, promulgated by the World Health Organization (WHO) (World Health Organization 1999), to define the ‘male factor’. Although of great importance and shortly to be updated, these criteria are of limited diagnostic value, and a significant proportion of men with normal conventional criteria of semen quality will be infertile because of defects in sperm function, while a significant number of men with abnormal semen quality will have normal sperm function. Very few studies on the epidemiology of male infertility have used functional, as opposed to descriptive, diagnostic criteria. Nevertheless, one common theme to emerge is that, using the available diagnostic techniques, male factor infertility is, in many studies, the most common single diagnostic category.

Pathophysiology

In the simplest terms, male infertility is a failure to fertilize the normal ovum arising from a deficiency of functionally competent sperm at the site of fertilization. Since less than 0.1% of ejaculated sperm actually reach the fallopian tube, it is defective sperm function rather than inadequate numbers of sperm ejaculated that constitutes the most important pathophysiological mechanism in male infertility. Specific lesions leading to defective sperm motility or transport and abnormal sperm–egg interaction are probably the key factors responsible for loss of fertilizing capacity in the gametes. In most instances, however, inadequate sperm function is usually but not invariably accompanied by reduced sperm production, suggesting that specific defects in spermatozoa commonly arise from disturbances in regulatory mechanisms which interfere with both germ cell multiplication and maturation in the seminiferous tubules. There is rarely any clinical evidence of systemic endocrine deficiency in men with male infertility. By inference, therefore, disturbances in paracrine regulation within the testis could lead to low sperm output (oligozoospermia), from an increased rate of degeneration in the differentiating spermatogonia at successive mitotic divisions, as well as abnormal spermiogenesis giving rise to spermatozoa with poor motility (asthenozoospermia) and/or abnormal morphology (teratozoospermia). Abnormal epididymal function may lead to defective sperm maturation, impairment of sperm transport or even cell death. Interruption of the transport of normal sperm may be due to mechanical barriers between the epididymis and fallopian tube or abnormal coitus and/or ejaculation.

Aetiology

Notwithstanding the difficulties in diagnosis outlined above, WHO has proposed a scheme for the diagnostic classification of the male partner of the infertile couple (Rowe 1993) (Box 21.1). This approach is of enormous value as a basis for standardization and for comparative multicentre studies. However, many of the male diagnostic categories are of a descriptive nature (e.g. idiopathic oligozoospermia) or of controversial clinical relevance (e.g. male accessory gland infection). Moreover, recent advances in our understanding of the causes of male infertility, particularly in the area of genetic problems (Hargreave 2000), mean that this classification is in need of review. The relative frequency of the major diagnostic categories is shown in Figure 21.6, using data taken from a WHO study of over 8500 couples from 33 centres in 25 countries (Comhaire et al 1987). It can be seen that the largest single male ‘diagnostic’ category was men with seminal abnormalities of unknown cause. Beyond this, varicocoele was a relatively common pathology, as was male accessory gland infection; however, systemic, iatrogenic and endocrine causes were very infrequent.

Figure 21.6 Aetiology of male factor infertility.

Adapted from Comhaire FH, de Kretser D and Farley TMM Towards more objectivity in diagnosis and management of male infertility. Results of a WHO Multicentre Study. International Journal of Andrology 1987; 10(S7): 1–53.

Genetic causes

Perhaps the most striking advances in our understanding of the aetiology of male infertility in the past decade have been in the area of genetics. Many of the ‘systemic’ disorders commonly associated with male infertility (see below) are now understood to have a genetic basis, and as our knowledge of the aetiology of disease expands, this will be increasingly the case. Traditionally, genetic causes of male infertility have been sought at the level of chromosomal abnormalities, with chromosomal abnormalities being detected in between 2.1% and 8.9% of men attending infertility clinics (Chandley 1994). The frequency of chromosomal abnormalities increased as sperm concentration declined, with abnormal karyotypes being found in 15% of azoospermic patients, 90% of whom had Klinefelter’s syndrome (47XXY), which accounted for half of the entire chromosomally abnormal group. In oligozoospermic patients, the incidence of chromosome abnormalities was 4%. However, it has been recognized for some time that structural anomalies of the Y chromosome, resulting in deletion of the distal fluorescent heterochromatin in the long arm, are associated with severe abnormalities of spermatogenesis. More recent studies have defined a family of genes on the Y chromosome involved in spermatogenesis, and it has become clear that a little over 10% of cases of non-obstructive azoospermia may have deletions affecting these genes. A proportion of cases of very severe oligozoospermia may have a similar aetiology. Microdeletions have been found in three non-overlapping regions of the Y chromosome, AZF a-b-c. Several genes have been described and these include RBM, DAZ, DFFRY, DBY and CDY. The abnormality most commonly reported in the literature is a microdeletion in the AZFc region and encompassing the DAZ gene. However, there is no exact correlation between DAZ deletion and the presence or absence of spermatogenesis, but this may be because of an autosomal copy of the DAZ gene (Hargreave 2000). DNA fragmentation has also been identified as the cause of defective sperm function (Tarozzi et al 2007). The ability of microassisted fertilization to overcome severe deficits in spermatogenesis has reinforced the importance of understanding and investigating genetic causes of male subfertility, as these will now be transmitted to the next generation of males.

Cryptorchidism

Undescended testis is a good example of a condition present at birth, and presumed to have its origins in intrauterine life, which is significantly associated with an increased risk of impaired spermatogenesis in later life and with an increased risk of testicular cancer (Irvine 1997). The testis which is not in a low scrotal position by the age of 2 years is histologically abnormal; spontaneous descent rarely occurs after 1 year and there is little evidence that surgical orchidopexy for an undescended testis after 2 years of age improves fertility. For these reasons, treatment should ideally be undertaken between 1 and 2 years of age. Evidence suggests that fertility may also be impaired in boys with retractile testis who experience spontaneous descent during puberty. Apart from the association with infertility, cryptorchidism is a well-established risk factor for testicular cancer, the risk of which in a patient with a history of undescended testis, whether successfully treated or not, is four to 10 times higher than in the general population.

Orchitis

Symptomatic orchitis occurs as a complication in 27–30% of males over the age of 10–11 years who suffer from mumps. In 17% of cases, orchitis is bilateral and seminiferous tubular atrophy is a common sequela of mumps orchitis, although recovery of spermatogenesis even after persistent azoospermia for 1 year has been reported (Sandler 1954). The prevalence of infertility after mumps orchitis is unknown, but fertility should only be impaired significantly if the orchitis is bilateral and occurs after puberty.

Varicocoele

The subject of varicocoele has generated controversy amongst the andrological community since the Edinburgh urologist Selby Tulloch first reported the apparently beneficial effects of treatment (Tulloch 1952). The available evidence certainly suggests that varicocoele is a common pathology and that it is more common in men with lower sperm counts. The diagnosis of visible (grade 3) and palpable (grade 2) varicocoeles is not difficult when the patient is examined in a standing position. The detection of subclinical (grade 1) varicocoeles, where spermatic vein reflux can only be detected during the Valsalva manoeuvre, requires more experience and has been aided by the use of Doppler or scrotal thermography. Prevalence figures from 5% to 25% have been reported in surveys of apparently healthy men (Hargreave 1994). In contrast, amongst men attending infertility clinics, varicocoele affects some 11% of men with normal semen and 25% of men with abnormal semen (World Health Organization 1992). The difficulty has been in establishing with certainty whether or not varicocoele affects spermatogenesis and, most importantly, whether or not treatment of varicocoele improves fertility, and if so, in which groups of men. It seems clear that varicocoele is associated with abnormal semen quality, and while the mechanism of this relationship remains to be established with certainty, abnormal testicular temperature regulation is known to be associated with varicocoele and impairment in semen quality.

Whatever the pathophysiology, there is a body of evidence suggesting that varicocoele causes progressive testicular damage, further complicating an assessment of its role in the aetiology of male infertility. Substantial controversy exists, however, over the question of whether or not the correction of varicocoele improves fertility (Evers et al 2008). Most of the appropriately designed controlled studies suggest that treatment is clearly associated with an improvement in semen quality; however, when the achievement of pregnancy is used as the endpoint, some studies find treatment to be effective while some suggest that it is of no benefit.

Occupational and environmental factors

The actively dividing male germ cells are one of the most sensitive cell types in the body with regard to the toxic effects of radiation, cytotoxic drugs and an increasing number of chemicals. Indeed, male gonadal function may be one of the most sensitive indices of overexposure to potential toxins (in the workplace, environment, foods, cosmetics and medicines) (Sharpe 2000, Bonde and Storgaard 2002). Data on occupational hazards to male reproduction remain controversial. Exposure to heavy metals, such as cadmium, lead, arsenic and zinc, has been reported to impair spermatogenesis, although the data are conflicting. Certain pesticides and herbicides have more clearly been shown to be toxic to spermatogenesis, as have some organic chemicals. The best documented modern example is the pesticide dibromochloropropane, which was responsible for azoospermic infertility in half of the male workers in a factory. There would seem to be clear evidence that occupational or environmental exposure to heat will have adverse consequences for spermatogenesis and will prolong time to pregnancy (Thonneau et al 1996). Recreational drugs such as cigarettes, alcohol and cannabis have all been linked with lower semen quality, and there is conflicting evidence on whether or not dress habit has a significant effect.

Recent data have demonstrated that male reproductive health is deteriorating, with evidence of a secular decline in semen quality (Carlsen et al 1992, Auger et al 1995, Irvine 1996), an increase in the incidence of congenital malformation of the male reproductive tract and an increase in the incidence of testicular cancer; however, there is, as yet, no evidence that these changes are having an influence on the prevalence of male infertility.

Iatrogenic infertility

Many general medical disorders are associated with male infertility, either directly (e.g. Kartagener’s syndrome), indirectly as a consequence of systemic disturbance (e.g. diabetes) or as a consequence of medical or surgical intervention on account of the primary disease. A number of pharmaceuticals can impair sperm production, the most common example in clinical practice today being sulphasalazine for the treatment of inflammatory bowel diseases. A number of other drugs are also associated with detrimental effects on spermatogenesis, including nitrofurantoin, anabolic steroids, sex steroids and anticonvulsants. Cytotoxic treatment regimes for Hodgkin’s disease, lymphoma, leukaemia and other malignancies damage the differentiating spermatogonia, so that most patients become azoospermic after 8 weeks. The degree of stem cell killing governs whether there is recovery of spermatogenesis or not after treatment. This is dependent on the cumulative dose of the drug combination used. Long-term follow-up has shown that following six or more courses of MOPP (mustine, vincristine, procarbazine and prednisolone), over 85% of patients remained azoospermic and recovery is unlikely after 4 years. Similarly, radiation exposure of over 6 Gy destroys germ cells with no chance of recovery. While 1–4 Gy produces complete cessation of spermatogenesis with only some stem spermatogonia surviving, there may be recovery after 12–36 months. Spermatogenesis may continue to improve for several years, but even then it may not be complete.

Genital tract obstruction

The combination of azoospermia, normal testicular volume and normal FSH are the hallmarks of genital tract obstruction. The incidence and relative importance of individual causes of obstruction differ according to geographic locality. Postcongenital and postvasectomy obstructions are the most common, but in some parts of the world, infectious causes, particularly gonorrhoea and tuberculosis, are of greater importance.

The most common congenital abnormality is agenesis or malformations of the Wolffian-duct-derived structures: the corpus/cauda epididymis, vas deferens and seminal vesicles. Diagnosis is usually quite easy; the scrotal vasa are not palpable and the ejaculate consists of low volumes (>1 ml) of acidic non-coagulating prostatic fluid devoid of fructose and sperm. Congenital bilateral absence of the vas deferens is associated with CFTR mutations and is found in approximately 2% of men with obstructive azoospermia (Hargreave 2000). In recent years, increasing numbers of mutations of the CFTR gene have been characterized and more than 400 have been described. In general, the more mutations tested for, the higher the percentage of men found to have mutations. As such, in more recent publications, detection rates have been almost 70–80%.

Male accessory gland infection

The second most common diagnostic grouping in the WHO survey is also an area of considerable aetiological controversy. Infection in the lower genital tract can be a treatable cause of male infertility, and the incidence varies in different communities. Gram-negative enterococci, chlamydia and gonococcus are established pathogenic organisms which usually produce unequivocal clinical evidence of infection (adnexitis), such as painful ejaculation, pelvic or sacral pain, urethral discharge, haematospermia, dysuria, irregular tender epididymides and tender boggy prostate. This can be confirmed by semen culture and urethral swabs. Inflammation of the accessory glands and excurrent ducts may give rise to disturbed function, formation of sperm antibody and permanent structural damage with obstruction in the outflow tract.

Thus, whilst there is little doubt that overt sexually transmitted disease may damage male fertility and should be appropriately managed, there is much more doubt about the relevance of subclinical infection. The entity of asymptomatic prostatitis is poorly defined and there is little evidence to support a genuine role for occult infections in male infertility. There is thus no place for microbiological screening investigations unless there is clinical suspicion of adnexitis. Furthermore, the isolation of non-pathogenic organisms such as staphylococcus, streptococcus, diptheroids, Ureaplasma urealyticum and Mycoplasma hominis, which are commensals in the normal urethra, does not warrant the indiscriminate use of antibiotics in the hope of correcting any abnormalities in the semen parameters.

One possible consequence of seminal leucocytosis is the excessive generation of reactive oxygen species (ROS). There is good evidence linking the excessive generation of ROS with male infertility as an aetiological entity in its own right; prospective studies have shown that couples with elevated levels of ROS generation are less likely to conceive either spontaneously or in the context of in-vitro fertilization (IVF).

Immunological causes

Suspected immunological infertility was found in some 3% of couples in a WHO survey on the basis of the finding of 10% or more of motile spermatozoa coated with antibody using assays such as the Immunobead test or the mixed antiglobulin reaction. Whilst antisperm antibodies are found in perhaps one in six of the male partners of infertile couples, a prevalence which is higher than that for fertile controls, their effect on fertility is hard to determine. Some studies suggest that ‘antibody-positive’ couples conceive at a lower rate than those without immunological problems. Unfortunately, antibodies to sperm surface antigens are also found in fertile control populations, and current techniques do not permit the meaningful separation of cases with autoimmunity to biologically relevant epitopes (Paradisi et al 1995). Given the consensus view that assisted conception is the treatment of choice, this may not now be a clinically relevant issue.

Gonadotrophin deficiency

The clinical features of gonadotrophin deficiency depend on the cause and time of onset, in particular whether the man is pre- or postpubertal. The spectrum includes patients with complete congenital deficiency in GnRH, which results in total failure of testicular and secondary sexual development. Other patients have less severe or partial GnRH deficiency, so have larger (4–10 ml) but still underdeveloped testes with more evidence of germ cell activity; this may be described as the so-called ‘fertile eunuch syndrome’. In three-quarters of these patients, anosmia or hyposmia and a variety of midline defects can be detected; this is the association known as ‘Kallmann’s syndrome’.

In contrast to these congenital varieties of isolated hypogonadotrophic hypogonadism, postnatally or postpubertally acquired gonadotrophin deficiency may arise from tumours, chronic inflammatory lesions, iron overload or injuries of the hypothalamus and pituitary, so that deficits in other pituitary hormones usually coexist. These patients have developed seminiferous tubules which have regressed through lack of trophic hormone support. Their testicular volumes are larger (10–15 ml) than in the former two groups.

Gonadotrophin treatment of these syndromes is discussed below. Androgen treatment is required by hypogonadal men for long-term replacement, and is generally given by injection of testosterone esters every 3–4 weeks, aiming to maintain plasma testosterone concentrations in the physiological range. This is made more difficult by the high peaks and low troughs following administration of these preparations; monitoring of dosage should take place immediately before subsequent injection (i.e. at the trough). Other preparations include the orally active testosterone undecanoate, transdermal patches, gels and subcutaneous testosterone pellets. Undecanoate is largely confined to paediatric practice for pubertal induction as circulating concentrations tend to be low. Testosterone patches frequently cause skin irritation, although this is not a problem with the gels as these do not contain the enhancers necessary to promote absorption across the skin. New injectable esters are becoming available with a longer duration of action, with up to 3 months between administration (Srinivas-Shankar and Wu 2006). Testosterone will restore sexual interest and activity, and penile erections during and on waking from sleep. Other symptoms of testosterone deficiency include tiredness, irritability and loss of body hair. Testosterone will not induce or improve fertility, and there is no place for androgen treatment of men wishing to conceive.

Coital disorders

Inadequate coital technique (including the use of vaginal lubricants with spermicidal properties) and frequency and faulty timing of intercourse may contribute to continuing infertility, but are rarely the only aetiological factors in the infertile couple. Erectile and ejaculatory failure may be caused by psychosexual dysfunction, depression, spinal cord injuries, retroperitoneal and bladder neck surgery, diabetes mellitus, multiple sclerosis, vascular insufficiency, adrenergic blocking antihypertensive agents, psychotrophic drugs, alcohol abuse and chronic renal failure. Primary endocrine pathologies such as androgen deficiency, hyperprolactinaemia and hypothyroidism seldom present with infertility without diminished libido and clinical features specific to the hormonal disturbances. Retrograde ejaculation must be differentiated from aspermia or anejaculation by examination of postejaculatory urine for the presence of spermatozoa.

Idiopathic impairment of semen quality

Regrettably, this descriptive label continues to be required for a very substantial proportion of men attending infertility clinics. Failure of seminiferous tubular function to the extent of producing azoospermia or severe oligozoospermia (>5 million) is usually associated with small (under 15 ml) and soft testes and elevated FSH. Histologically, the tubules may show completely absent or reduced numbers of germ cells, narrow tubular diameter, and thickening and hyalinization of peritubular tissue. These changes are non-specific and are not always uniformly distributed throughout the testes. There is no evidence to support the contention that testosterone deficiency is the primary cause of defective spermatogenesis, nor that abnormalities in GnRH pulse frequency may be the underlying cause of idiopathic hypospermatogenesis. These patients usually remain infertile and there is no curative treatment available. Less severe degrees of oligozoospermia are commonly associated with abnormal morphology and reduced motility.

‘Asthenozoospermia’ is the descriptive term applied to impaired sperm motility. Absent or extremely low sperm motility of only 1–2% may result from absence of dynein arms, radial spokes or nexin bridges, and dysplasia of fibrous sheath. This is associated with similar defects in respiratory cilia and therefore, frequently, a history of chronic respiratory infection, bronchiectasis and sinusitis: the ‘immotile cilia syndrome’. In addition, some of these patients have situs inversus (Kartagener’s syndrome). Based on this classic but extremely rare example, it is now becoming clear that more common but less severe degrees of asthenozoospermia may also be associated with more subtle structural malformations in the axonemal complex, recognizable only with ultrastructural examination and functionally evident as suboptimal sperm movements.

‘Teratozoospermia’ is the term used to describe altered morphology. Surface morphology directly reflects the maturity and functional integrity of the spermatozoa so that morphological analysis of ejaculated sperm is an important means of assessing spermatogenesis in the testis. Indeed, some workers believe that sperm morphology is the best predictor of spontaneous fertility or the outcome of IVF (Kruger et al 1995). It has been reported that morphology in the individual spermatozoon is related to movement characteristics (swimming velocity, sperm head trajectories, flagellar beat frequency) and its ability to exhibit hyperactivation. Similarly, the ability to undergo the acrosome reaction has also been shown to be significantly higher in sperm with morphologically normal, compared with abnormal, sperm heads. Ultrastructural studies have also revealed a variety of structural malformations of the acrosome complex, the most extreme example being the round-headed sperm where the acrosome is completely missing, but lesser degrees of acrosomal defects are increasingly being identified. These attempts to relate specific functional defects to recognizable structural malformations in individual spermatozoa provide evidence that morphologically abnormal sperm are also functionally impaired.

History

Infertility is, of course, the problem of a couple and must be managed as such, with the history being taken from both partners together. The duration of the present union and the duration of infertility complained of should be established at the outset, together with the history of any pregnancies for which the individual may have been responsible. In the patient’s past medical history, areas which should receive special attention are a history of mumps virus infection, the age at which this occurred and whether or not there was an associated orchitis. As can be seen from Table 21.1, 84% of men with a history of bilateral mumps orchitis have abnormal semen and 22% are azoospermic. Diabetes mellitus and certain neurological diseases are known to be associated with ejaculatory disturbances, and a history of these or of any other systemic illness should be sought, as should a history of recent pyrexial illness as this may compromise spermatogenesis for many weeks. A history of respiratory disease should be sought carefully, including recurrent respiratory tract infections, sinusitis, bronchiectasis or cystic fibrosis, as these conditions can be associated with ciliary dysfunction and therefore with impaired sperm motility, as in Kartagener’s syndrome, or with obstructive azoospermia, as in Young’s syndrome. As many as 82% of men with a history of bronchiectasis have abnormal semen and 32% are azoospermic. Parasitic diseases, such as schistosomiasis and filiariasis, are rare but must be borne in mind as potential causes of excurrent duct obstruction and prostatovesiculitis.

Any symptomatology related to the urinary tract, such as dysuria, urethral discharge, frequency or haematuria, is of self-evident importance. Likewise, aspects of the specific reproductive history which are of importance include any history of testicular maldescent, injury, torsion or epididymo-orchitis, and any history of surgery which may have compromised the genital tract, such as herniorrhaphy, orchidopexy, drainage of hydrocoele, ligation of a varicocoele or bladder neck surgery. Other specific conditions may impair reproductive performance, and a group of patients now requiring infertility investigations are those who have survived treatment for testicular or lymphatic malignancy and who may suffer the consequences of chemotherapy, radiotherapy or retroperitoneal lymph node dissection. A history of drug ingestion, including sulphasalazine, cimetidine or nitrofurantoin, or of exposure to other toxins, including alcohol and tobacco, known to impair spermatogenesis is important, as is the occupational history in terms of exposure to toxic chemicals and hyperthermia. The sexual history should endeavour to cover the adequacy of erectile function and if there is doubt, the presence of early morning and masturbatory erections should be enquired into in order to differentiate organic from psychogenic impotence. The occurrence of intravaginal ejaculation should be established and again, if there is doubt, the occurrence of nocturnal or masturbatory ejaculation sought, in addition to which the characteristics of ejaculation such as associated pain, prematurity or delay should be established. A number of couples attending infertility clinics will be infertile as a consequence of sexual dysfunction, and a number of couples with sexual dysfunction will present to infertility clinics seeking primary help. Of course, any history of sexually transmitted disease and its outcome is of note, as is a history of drug abuse or of other factors exposing the patient to high risk of infection with human immunodeficiency virus, due to the problems which this poses for the couple in terms of the risks of transmission and pregnancy, and in terms of the problems presented to laboratory staff handling blood and semen samples.

Examination

The examination of the male partner should include a general medical examination covering height and weight, blood pressure and all of the major systems, including the respiratory system. The secondary sexual development of the patient must be assessed and signs of hypogonadism sought, including examination of the visual fields, to assess pituitary enlargement, and examination of the sense of smell to exclude Kallmann’s syndrome if indicated. Gynaecomastia should be specifically examined for in this context. On examination of the abdomen, it is important to note the presence of scars or lymphadenopathy in the groins.

Turning to the urogenital examination, the penis is examined for evidence of phimosis, hypospadias, epispadias or the characteristic plaques of Peyronie’s disease. The scrotum should be examined and the site of the testes determined, following which the testicular volume in millilitres should be determined with the aid of a Prader orchidometer (Figure 21.7) and their consistency evaluated. It is known that a clear relationship exists between testicular volume and sperm production. Any tenderness of the gonads should be noted and the epididymides carefully palpated from caput to cauda to exclude thickening, tenderness, cystic lesions, atrophy or absence of the epididymides. The vasa deferentia should next be palpated to establish that they are not congenitally absent and any thickening or induration should be noted. Scrotal swellings, such as hydrocoele or hernia, should be noted and the presence and grade of varicocoele should be established by asking the patient to perform Valsalva’s manoeuvre. The inguinal regions should be inspected for hernia, scarring or the presence of lymphadenopathy. A rectal examination should be performed to assess the state of the prostate and seminal vesicles, although this seldom provides useful information and may be omitted unless ejaculatory duct obstruction or prostatovesiculitis is suspected.

Figure 21.7 Prader orchidometer for the assessment of testicular volume.

From L Hagenäs, Normal och avvikande pubertet hos pojkar, Journal of the Norwegian Medical Association, 2008; 128:1284–8.

Semen analysis

The conventional criteria of semen quality have changed little since van Leeuwenhoek first described spermatozoa in the human ejaculate in 1685. A standard semen analysis, performed according to clearly established guidelines promulgated by WHO (World Health Organization 1999) (Box 21.2), provides descriptive information concerning sperm number, motility and morphology, together with aspects of the physical characteristics of the ejaculate.

Hormone measurements

The measurement of plasma FSH is useful in distinguishing primary from secondary testicular failure and in identifying patients with obstructive azoospermia. In the presence of azoospermia or oligozoospermia, an elevated FSH, particularly with reduced testicular volume, is presumptive evidence of severe and usually irreversible seminiferous tubular damage. Low or undetectable FSH (usually associated with low LH and testosterone, with clinical evidence of androgen deficiency) is suggestive of hypogonadotrophism. Conversely, azoospermia with normal FSH and normal testicular volume usually indicates the presence of bilateral genital tract obstruction. Occasional exceptions to these general rules occur from time to time, as azoospermic men with the Sertoli cell only syndrome may have normal FSH levels, while some men with high FSH may have normal spermatogenesis.

Testosterone and LH measurements are indicated in the assessment of the infertile male when there is clinical suspicion of androgen deficiency, sex steroid abuse or steroid-secreting lesions such as functioning adrenal/testicular tumours. In men presenting with infertility, testosterone is usually within the normal range although some degree of Leydig cell dysfunction, as evidenced by statistically lower testosterone and higher LH compared with normal, is not uncommon. This may identify those who may be considered for androgen replacement, although this has no bearing on fertility. High LH and testosterone should raise the possibility of abnormalities in androgen receptors, while low LH and testosterone suggest hypogonadotrophism.

Hyperprolactinaemia is not a frequent cause of male infertility, but prolactin measurement should be undertaken if there is clinical evidence of sexual dysfunction (particularly loss of interest in sex) or pituitary disease leading to secondary testicular failure. Oestradiol measurement is rarely indicated except in the presence of gynaecomastia, which is also a feature of Klinefelter’s syndrome.

Dynamic tests of pituitary–testicular function such as GnRH, thyrotrophin-releasing hormone and human chorionic gonadotrophin stimulation generally do not add to the basal measurements described above. Bearing in mind the episodic nature of LH secretion, the diurnal variation in testosterone and the stress-related secretion of prolactin, it is usually sufficient to repeat their measurements in the morning, under resting conditions if necessary.

Chromosome analysis

Chromosome karyotyping should be carried out in patients with azoospermia or severe oligospermia with reduced testicular volumes and elevated FSH. Cytogenetic abnormalities, by far the most common being Klinefelter’s syndrome, may be detected in approximately 10% of this group and are of importance if treatment by ICSI is being contemplated. Although still only research, screening for microdeletions on the Y chromosome is likely to enter routine clinical practice in the near future (Krausz and Degl’Innocenti 2006).

Testicular biopsy

With the use of plasma FSH to differentiate between primary testicular failure and obstructive lesions, the need for testicular biopsy in the investigation of male infertility has largely been superseded, although it clearly has a place in the surgical retrieval of sperm for ICSI. When genital tract obstruction is suspected, testicular biopsy is useful in confirming normal spermatogenesis and excluding spermatogenic arrest, but should only be undertaken under circumstances where sperm may be stored for subsequent use in assisted conception. When the clinical differentiation between spermatogenic failure and obstruction is uncertain (e.g. asymmetrical findings on examination between right and left testes or adnexae), scrotal exploration with testicular biopsy may be helpful, again with facilities for sperm storage to hand. Vasography during scrotal exploration is required to confirm the diagnosis of obstructed ejaculatory ducts. It is important to remember that even in primary testicular failure with small testes, elevated levels of FSH and a testicular biopsy showing Sertoli cell only syndrome, some areas of spermatogenesis may be present in the testis. There are many techniques for describing the appearances of a testicular biopsy, but the combination of words and a qualitative assessment, using Johnsen scoring (Johnsen 1970), is useful. In the Johnsen score, the histological features of spermatogenesis are scored from 1 to 10 (2, Sertoli cell only; 3, spermatogonia; 4, 5, spermatocytes; 6, 7, spermatids; 8, 9, 10, spermatozoa).

Treatment

The management of male infertility often remains a difficult and somewhat unsatisfactory experience for patients as well as doctors. Many patients present no recognizable or reversible aetiological factors for treatment, and the doctor frequently fails to appreciate that normal semen values do not relate to fertility. In recent years, there have been a number of advances which have made a significant impact on our therapeutic capabilities. It is important to improve semen quality and to treat those factors that impair fertility.

Assisted conception and male infertility

Early developments in IVF focused on couples with female factor infertility and particularly women suffering from bilateral tubal occlusion. Conventional IVF rapidly became established as an effective treatment option for couples with tubal disease and with unexplained infertility, but it soon became apparent that it yielded generally poor pregnancy rates for couples with male factor infertility. Although there was much discussion in the literature on the fine tuning of the IVF procedure for couples with problems in the male partner, management options for couples with poor semen quality remained very limited until the breakthrough of effective microassisted fertilization in 1992 (Palermo et al 1992).

Testicular cancer

Although many of the changes seen in male reproductive health are controversial, there seems little argument that testicular cancer is increasing in frequency, with unexplained increases in the age-standardized incidence being observed in Europe (Adami et al 1994, Bergstrom et al 1996) and the USA (Devesa et al 1995). There would appear to be substantial geographical variation in both the incidence of testicular cancer and in the observed rate of increase (Adami et al 1994). Of note, this geographical variation may be linked with that seen in semen quality; testicular cancer is four times more common in Denmark, where studies have revealed rather low sperm counts (Jensen et al 1996), than in Finland, where semen quality appears to be better (Vierula et al 1996). Interestingly, the observed increases, both in Europe and the USA, would appear to be birth cohort related. Bergstrom et al (1996) evaluated data from Denmark, Norway, Sweden, East Germany, Finland and Poland, including data on over 30,000 cases of testicular cancer from 1945 to 1989 in men aged 20–84 years. They found considerable regional variation in both the incidence of testicular cancer and the observed rate of increase, ranging from a 2.3% increase annually in Sweden to a 5.2% increase annually in East Germany. In all six countries, birth cohort was a stronger determinant of testicular cancer risk than calendar time, such that men born in 1965 had a risk of testicular cancer that was 3.9 times [95% confidence interval (CI) 2.7–5.6; Sweden] to 11.4 times (95% CI 8.3–15.5; East Germany) higher than that for men born in 1905.

A recent study has looked in detail at the risk of testicular cancer in subfertile men (Moller and Skakkebaek 1999) using a population-based case–control design. This study found that paternity was associated with a reduced risk of testicular cancer (relative risk 0.63, 95% CI 0.47–0.85), and that prior to the diagnosis of testicular cancer, cases tended to have fewer children than expected for their age (relative risk 1.98, 95% CI 1.43–2.75). The study suggested that these observations are consistent with the hypothesis that testicular cancer and male subfertility share important aetiological factors.

Cryptorchidism and congenital malformations of the male genital tract

The incidence of congenital malformation of the male genital tract may also be changing, with increases observed in the prevalence of cryptorchidism and hypospadias. Cryptorchidism, for example, has increased by as much as 65–77% over recent decades in the UK (Ansell 1992). In contrast, some data from the USA have tended to suggest that rates of cryptorchidism have not changed (Berkowitz et al 1993), although one recent large study from the USA reported that rates of hypospadias doubled from the 1970s to the 1980s (Paulozzi et al 1997). Here too, though, regional differences have been observed, although the data are perhaps less robust than is the case with testicular cancer. One multicentre study of 8122 boys from seven malformation surveillance systems around the world concluded that, even when differences in ascertainment were taken into account, true geographical differences exist in the prevalence of hypospadias at birth (Kallen et al 1986).

Changing semen quality: historical data on normal men

In 1992, Carlsen et al (1992) reawakened concern over the possibility of secular trends in semen quality, publishing a meta-analysis of data on semen quality in normal men. The authors undertook a systematic review of available data on semen quality in normal men, published since 1930. Standard techniques applicable to meta-analysis were used to identify relevant papers, and care was taken to exclude data on infertile couples, men selected on the basis of their semen quality and data generated using non-classical approaches to semen analysis. Data were obtained on 14,947 men, published in 61 papers between 1938 and 1990. The authors observed a decline in sperm concentration from 113 × 10⁶/ml in 1940 to 66 × 10⁶/ml in 1990, along with a decline in the proportion of men with a sperm concentration above 100 × 10⁶/ml. Predictably, the central message of this meta-analysis, that sperm counts had declined by approximately 50% over the past 50 years, attracted enormous attention and generated much controversy.

Since publication of Carlsen et al’s meta-analysis, several papers have presented contemporary analyses of retrospective data. Unfortunately, the available data still fail to reach a conclusion on whether or not there is any secular trend in semen quality; at least as many studies have reported evidence of deteriorating semen quality as have reported evidence of no change. A very careful reanalysis of the historical data (Carlsen et al 1992) on semen quality in normal men (Swan et al 1997) found that there was evidence of a decline in sperm concentrations in the USA of −1.5 × 10⁶/ml/year (95% CI −1.9 to −1.1), and in Europe of −3.13 × 10⁶/ml/year (95% CI −4.96 to −1.30), but not in non-Western countries.

Whilst the available evidence is inconclusive and circumstantial, its weight is considerable and, at the very least, it should raise concerns that deserve to be addressed by properly designed, coordinated and funded research. Delay may compromise the fertility and reproductive health of future generations (de Kretser 1996, Irvine 1996).