Anterior Sacral Meningocele

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Chapter 118 Anterior Sacral Meningocele

John A. Lancon, Edward C. Benzel, Robert E. Tibbs, Jr.

Sacral meningocele may be congenital or acquired. Most acquired sacral meningoceles are a consequence of dural ectasia in association with the neurofibromatoses, Marfan syndrome, and Ehlers-Danlos syndrome.¹^–⁶ These meningoceles usually are single and may expand into the intrasacral, presacral, and parasacral spaces. Traumatic avulsion of sacral nerve roots may produce sacral pseudomeningoceles in conjunction with profound neurologic deficits.^7,⁸ These sacs are more likely to be multiple and located in the lateral presacral space.

The congenital anterior sacral meningocele (ASM) was first described by Bryant in 1837.⁹ It is rare in comparison to its dorsal counterpart. Matson noted only three examples in his analysis of 1390 cases of spina bifida cystica.¹⁰ A congenital ASM characteristically occurs as a cystic presacral mass connected to the caudal thecal sac by a pedicle of variable size. Meningocele volumes as large as 1 to 2 L have been described.¹¹^–¹³ Anorectal, genitourinary, and sacral anomalies also may be present.

In addition to the reported incidence, congenital ASM and dorsal lumbosacral meningocele differ from one another with respect to their pathogenesis, presentation, prognosis for neurologic improvement, and surgical approaches. Both anomalies may be associated with significant morbidity and mortality if not managed in a logical fashion, based on an understanding of their pathogenetic origins and surgical anatomy. This chapter reviews the pathogenesis, clinical presentation, and preoperative evaluation of congenital ASM. Needle aspiration and surgical approaches, including the transabdominal-transpelvic, presacral, parasacral, and dorsal transsacral routes, are described. In addition, guidelines for the avoidance and management of perioperative complications are reviewed.

Pathogenesis

The processes of spine and spinal cord development span the period from embryogenesis to postnatal development. Similar to more rostral vertebrae, the sacral vertebrae develop from sclerotomes. However, the sacral pattern requires additional centers of ossification. This process occurs slowly and is not completed until the third or fourth decade of life. Developmental sacral osseous anomalies (mesodermal) include sacralization of lumbar and coccygeal segments; lumbarization of the first sacral segment; stenosis or dilatation of the sacral foramina; isolated defects of the dorsal, lateral, and ventral elements; and sacral agenesis.¹⁴

The sacrococcygeal neural elements develop after closure of the posterior neuropore. Beneath an intact surface ectoderm, the caudal cell mass enlarges and undergoes canalization. This occurs from the 4th to 6th weeks of life, forming spinal cord segments extending from S2 to S3 to the coccygeal terminus. Extensive cellular degeneration along the distal neural tube produces a fibrous remnant at the caudal-most tip of the developing CNS. This remnant becomes the filum terminale. The ventriculus terminalis lies at the level of the S5 entry zone, marking the point of transition between the conus medullaris and filum terminale.¹⁴ Lying at the distal end of the filum terminale, the coccygeal medullary vestige may be the origin of the intrasacral meningocele.¹⁵^–¹⁷

Before the 9th week, spinal cord and vertebral segments are aligned level for level. With the dura mater now forming a complete covering, the spinal cord and dura mater begin to ascend in relation to the growing vertebral column, albeit at different rates. The conus medullaris rises to L3 at birth and to L1-2 by 3 months. The dural sac constricts terminally, rising only to S4 at birth and to S2-3 in the adult. Developmental sacrococcygeal neuroectodermal anomalies include meningocele, myelomeningocele, lipomyelomeningocele, myelocystocele, anomalies of the conus medullaris, tethered filum terminale, intrasacral meningocele, and caudal regression syndromes.¹⁴

In contrast to dorsal meningoceles that arise from failure of the posterior neuropore to close or dehiscence of a formed neural tube, a congenital ASM arises after failure of one or more sacral sclerotomes to develop. The meningeal sac expands through the sacral defect driven by cerebrospinal fluid (CSF) pulsations. The sacral defect enlarges only slightly, while the developing pelvic viscera offer less resistance to the budding meningocele. The sac enlarges tremendously in the presacral space, remaining attached to the thecal sac by a smaller pedicle. Although spontaneous regression of the meningocele does not occur after birth, progressive enlargement may occur and is associated with the development of symptoms. The large volume attained by some meningoceles causes crowding of the pelvic viscera.¹¹ The ventral sacral defect is usually parasagittal, less commonly midline or lateral. The typical anatomic relationships of an anterior sacral meningocele are depicted in Figure 118-1.

FIGURE 118-1 Illustration of a typical anatomic scenario regarding a congenital anterior sacral meningocele. Intrathecal (filum terminale), intracystic, and extracystic-intrapelvic tumors may be associated.

Complex interactions between adjacent germ cell substrata in the embryonic caudal midline give rise to varying cascades of maldevelopment, which include a spectrum of mesectodermal dystrophies. The embryologic event that initiates these patterns of maldevelopment is distinct from the insult that causes failure of the posterior neuropore to close. Although the precise event is not clearly defined, evidence for a vascular etiology exists.^14,^18,¹⁹ In addition to anomalies of the conus medullaris, sacral nerve roots, and sacral dura mater, the clinical manifestations of these patterns of maldevelopment include the development of congenital tumors (e.g., dermoid, epidermoid, hamartoma, lipoma, teratoma, and teratocarcinoma) and anomalies of the colorectal, genitourinary, and reproductive systems.^2,^14,²⁰^–²⁴

Most congenital ASMs appear to occur sporadically, although familial and X-linked dominant inheritance have been reported.^20,^23,^25,²⁶ The seemingly greater incidence in females is a manifestation of the tendency toward symptomatology in the presence of sacral crowding, as well as the greater likelihood that female patients in the second and third decades of life will undergo palpation of the presacral space during routine physical examination. When cases in patients under 20 years of age are considered, the female-to-male ratio is approximately 1:1.^12,²⁷

Clinical Presentation

Congenital ASM has a trimodal pattern of presentation.^2,^12,^13,^24,²⁸^–³² Some ASMs are recognized at birth, when they are discovered in association with anorectal anomalies and sacral defects (Currarino’s triad).³³ Most commonly, however, ASMs present during the first and second decades of life with progressive constipation or other symptoms referable to the colorectal, genitourinary, and reproductive systems.^2,^12,^13,^24,^27,^29,³⁰^–³² ^,34 ^,35 Less commonly, low back pain, headache, or sacral radiculopathy may be the initial manifestation.^12,^13,²²

A small congenital ASM may remain occult for life, particularly in the male patient.^12,¹³ Occasionally, a meningocele is discovered incidentally during the initiation of routine prenatal care in a new mother. In the rare case of a pregnant woman with no prenatal care, the meningocele may present as dystocia. In this setting, the characteristically benign ASM may threaten serious morbidity and even death.

Colorectal

The most common symptom in patients with congenital ASM is chronic constipation or obstipation, usually manifesting in the first two decades of life. Fecal incontinence and soiling rarely predominate in the clinical picture. Communication between congenital ASM and the rectum may be congenital or acquired and may produce fulminant meningitis. The anal canal may be duplicated or atretic.^12,^13,²⁰

Genitourinary

Urinary incontinence may be due to tethering of the spinal cord or direct pressure on the bladder, ureters, or S1, S2, and S3 nerve roots, or, rarely, may be the result of congenital deficits in the innervation of the lower urinary tract. Enuresis and recurrent infections affecting either the upper or the lower tract may occur. Coexisting anomalies include horseshoe-shaped kidneys and duplication of the kidneys, renal pelvis, or ureter.^12,¹³

Reproductive

Dysmenorrhea, dystocia, and dyspareunia occur less commonly. Dysmenorrhea may be secondary to compression of retropelvic veins resulting in pelvic venous congestion. Duplication of the uterus and vagina and vaginal atresia may be present.^12,^13,²¹

Neurologic

True neurologic symptoms are rare and typically are mild when present because the distal spinal cord and nerve roots develop normally. However, progressive leg or perineal weakness, numbness, and pain may develop as a result of stretching of the sacrococcygeal nerve roots by the meningocele.^12,^13,²⁷ These patients usually will have some symptoms suggestive of involvement of the pelvic visceral innervation. Chronic pelvic pain may occur due to involvement of the pelvic autonomic plexi. Such symptoms typically are progressive and do not develop until later in life, implying the potential for reversibility after treatment if they are recognized early. Coexisting tethering of the spinal cord actually may lessen the amount of tension exerted on the nerve roots by the enlarging meningocele.² The presence of severe neurologic dysfunction from birth indicates a more severe myelodysraphic state and is associated with a greater tendency toward anomalous development in adjacent viscera. The patient whose clinical picture is characterized by prominent sacrococcygeal radiculopathy that worsens after a Valsalva maneuver is more likely to harbor an intrasacral meningocele or an ASM based on a large pedicle.^2,^12,^13,^15,¹⁷ The sacrococcygeal radiculopathies are listed in Table 118-1.

TABLE 118-1 Sacrococcygeal Radiculopathies

Mild to moderate headache-associated symptoms may occur and are of two forms.^2,^27,^31,³⁶ A high-pressure variant secondary to pressure exerted on the meningocele during pregnancy or after a Valsalva maneuver has been reported occasionally; less commonly, a low-pressure headache may occur on rising to the standing position, caused by the displacement of CSF from the thecal sac into the meningocele. Pressure-related headaches are more likely in the presence of a large communication between the thecal sac and the meningocele.^12,¹³

Congenital ASM may be a cause of meningitis. Bacterial meningitis resulting from erosion of the meningocele into the bowel or bladder lumina or resulting from the presence of a congenital rectothecal or vesiculothecal fistula and aseptic meningitis resulting from leakage of an intraspinal dermoid cyst have been described.^2,^23,²⁷

Preoperative Evaluation

The most consistent physical finding in congenital anterior sacral meningocele is a soft, cystic, retrorectal mass that appears fixed to the sacrum.^12,¹³ The mass is felt most commonly on rectal examination but may be felt on pelvic, abdominal, gluteal, or inguinal examination as well. A transmitted pulse wave sometimes may be appreciated with a Valsalva maneuver.^12,¹³ Dyck and Wilson³⁷ described a patient who presented with a sliding groin hernia and was found to harbor a congenital ASM. They postulated crowding of the pelvic viscera as a significant contributing factor in the development of the hernia, which contained a portion of the urinary bladder.

Although a congenital ASM usually can be felt easily on rectal or pelvic examination, the main limitation to premorbid discovery is a failure to suspect its presence. This failure is a result of both its secluded location within the deep pelvis and the great variety of typically mild, nonspecific symptoms with which it presents. The evaluation of a male or female patient presenting within the first three decades of life with progressive constipation or obstipation should include a careful history and physical examination directed toward the gastrointestinal, genitourinary, and reproductive systems. Specific examination of the sacrococcygeal innervation should be performed.