Subfalcine (cingulate gyral) herniation

With a parasagittal mass, the ipsilateral cingulate gyrus may herniate beneath the free edge of the falx (Fig. 24.3A). The anterior cerebral artery may be compressed sufficiently to cause medial hemispheric infarction, but otherwise there are no obvious clinical signs except deteriorating conscious level.

Fig. 24.3 Herniation syndromes.

A Coronal diagram of the dynamics of an intracranial mass lesion. Tumour (T) causes mass effect that compresses the midline and the ventricles (unnumbered arrows), provoking subfalcine or cingulated herniation (arrow 1), and transtentorial herniation (arrow 2). If the mass effect is uncontrolled, tonsillar herniation may also occur (arrows 3). B Transtentorial herniation in the axial plane (plane of dotted line in Fig. 24.3A). C Foraminal herniation.

Transtentorial (uncal) herniation

With large ipsilateral brain lesions, the medial part of the temporal lobe is pushed down through the tentorial notch to become wedged between the tentorial edge and the midbrain (Fig. 24.3B). The opposite cerebral peduncle is pushed against the sharp tentorial edge, and the midbrain and uncus become wedged at the tentorium. The aqueduct is compressed, obstructing CSF flow, and venous obstruction leads to midbrain haemorrhage. The clinical features of an uncal herniation, most often due to a traumatic intracranial haematoma, are:

Table 24.1 Glasgow Coma Scale

Saccular intracranial aneurysms

Risk factors include smoking, hypertension, polycystic disease of the kidney and female gender. The median age of affected patients is 47 years, although familial aneurysms may rupture earlier. Most aneurysms (85%) affect the anterior circulation and 15% of patients have more than one. The majority have no symptoms until rupture occurs, although a few may suffer compressive symptoms, and ectatic aneurysms may not rupture at all but cause symptoms by embolic phenomena. The most common compressive clinical signs are features of oculomotor nerve (CN III) palsy due to an aneurysm of the posterior communicating artery. Many intracranial aneurysms are now discovered as incidental findings when the brain is imaged.

Investigations

The standard investigation is CT, which characteristically shows blood in the CSF basal cisterns in the acute phase (Fig. 24.4). As CSF blood is broken down, the CT detection rate falls after the first 72 hours. If the diagnosis is in doubt, then a lumbar puncture should be performed, but only in patients whose clinical condition is good and in whom CT has excluded an intracranial mass lesion or midline shift. If this is performed early, the CSF will be uniformly blood-stained; later it will contain haem pigments that will be apparent on naked-eye inspection (xanthochromia) or can be detected by spectrophotometry.

Fig. 24.4 Axial CT scan of a patient following subarachnoid haemorrhage.

Blood is seen in the basal cisterns as a white lesion (solid arrow), and also in the fourth ventricle (broken arrow). There is early enlargement of all ventricles. Courtesy of Dr R Gibson.

Next, a search must be made for the site of the bleeding. About 80% of aneurysms involve the anterior circulation. Conventionally, carotid or vertebral angiography has been performed (Fig. 24.5). However, CT and MR angiography are equally good at revealing aneurysms greater than 5 mm, and are non-invasive and so associated with less morbidity. As the consequences of missing a diagnosis of SAH are serious, there is a tendency to perform angiography in patients in whom the diagnosis is equivocal. For that reason, a source of bleeding will be identified in only 70% of angiograms. This is usually an aneurysm, less commonly an AVM or a cavernoma. In 30% of cases, no source is found. In the majority, this is a ‘true’ negative, and many of these patients will have a condition called perimesencephalic SAH, which is of unknown aetiology.

Fig. 24.5 Intra-arterial digital subtraction angiogram outlining the cerebral vasculature and showing an aneurysm of the anterior communicating artery (arrow).

Management of aneurysmal SAH

The medical management of SAH includes intravenous fluids; the calcium antagonist, nimodipine (EBM 24.1); analgesia; and antiemetics. Patients in coma will usually be intubated and managed in a neurointensive care unit. Having initially been quite well, many patients begin to exhibit signs of focal or global cerebral ischaemia 4–10 days following an SAH. This has been attributed primarily to vasospasm and can be ameliorated by the prophylactic use of nimodipine; however, clinical deterioration may occur due to hydrocephalus, seizures, metabolic abnormalities and systemic infections.

Rebleeding is a major cause of morbidity and mortality following aneurysm rupture. Until recently, standard management was occlusion of the aneurysm from the cerebral circulation by surgically clipping its neck (Fig. 24.6 and EBM 24.2). However, it is now possible to place detachable coils within the aneurysm via a catheter passed from the femoral artery into the cerebral circulation (Fig. 24.7). The coils unwind in the aneurysm and induce thrombosis. Coiling is a much less invasive procedure than open surgery and a recent prospective randomized controlled trial showed that, when an aneurysm can be treated by surgery or coiling, the latter is safer (EBM 24.3). Previously, only a proportion of aneurysms were suitable for coiling. However, improvements in coil, stent and basket technology mean most aneurysms can now be coiled.

Fig. 24.6 Cerebral arteries at postmortem showing a surgical clip (broken arrow) on a ruptured middle cerebral artery aneurysm (MCA).

There is also a non-ruptured carotid bifurcation aneurysm (arrow). (ICA = internal carotid artery)

Fig. 24.7 Middle cerebral artery aneurysm.

A Digital subtraction angiogram showing the aneurysm (arrow). B Its occlusion from the cerebral circulation after coiling (arrows).

Even when an aneurysm has been successfully excluded by means of coiling or surgery, the patient can still suffer stroke. Although nimodipine has significantly decreased the risk of stroke (to 23%) and death (to 22%), there is still no effective treatment for delayed cerebral ischaemia following SAH. Clinical practice has included induced hypertension and plasma volume loading (to keep up CPP), as well as haemodilution (to reduce blood viscosity in the hope of increasing flow), but this triple therapy has its own problems, such as heart failure. The outcome following aneurysmal SAH is heavily dependent upon the condition of the patient on admission and the CSF blood load (the more blood, the worse the outcome). Patients admitted in good condition (grade 1) enjoy a complete recovery in about 90% of cases. By contrast, about 50% of those admitted in coma (grade 5) die or are severely disabled. The outcome of intermediate patients is unpredictable and not necessarily dependent on the clinical excellence of either the attending surgeon or interventional neuroradiologists. Hypotension and fever are also associated with poorer outcome.

Glasgow Coma Score

The GCS is a measure of conscious level that has greatly facilitated the classification and objective management of head-injured patients. It is used internationally and records the best verbal response, best motor response and eye opening. The maximum score is 15 and the minimum is 3. Change in GCS over time is much more informative than an absolute reading at any one point in time. The Glasgow Coma Scale can be used in children of all ages, although the ‘best verbal’ component of the scale needs to be modified to take into account the age of the child, particularly in children under the age of 4 years. The best postresuscitation GCS is used to classify severity of head injury. Mild injury is GCS from 15 to 13; moderate is from 12 to 9; and less than 8 is classified as severe. Coma is also defined as a GCS of 8 or less.

Neurological examination

This should include routinely an assessment of pupil size and reaction; a search for CSF leaks from nose, mouth and ears; a survey of the scalp for penetrating injuries; signs of a basal skull fracture (Battle’s sign, raccoon eyes); and an assessment of the maxillofacial skeleton. Peripheral neurological examination will give a guide to focal brain injury, spinal injury or peripheral nerve injury.

Other systems

Patients with head injury often have extracranial injury. It is important to remember that head injury alone never causes hypovolaemic shock. The management of systemic complications such as severe chest injury, intra-abdominal haemorrhage or major volume loss is a priority in treatment, since these phenomena will lead to secondary cerebral ischaemia and hypoxia and thus secondary brain damage.

Cervical spinal injury

This is commonly caused by trauma that produces subluxation of the cervical vertebra, often C5 on C6, a crush fracture of a cervical vertebral body, or hyperextension or hyperflexion injury in a patient with a narrow cervical spinal canal. The resulting neural injury may cause quadriparesis or a complete cord transection syndrome. A common pattern of injury in the elderly is a central cord syndrome, in which the segmental grey matter is contused but the fibre tracts are relatively spared. This produces weakness in the upper limbs, but relative sparing of the lower limbs.

Management consists of prompt recognition of the injury. Patients will have variable neurological deficits. With cord transection, there may be hypotension and bradycardia (due to loss of peripheral sympathetic tone), areflexia, hypotonicity and paresis. Sensory examination provides a clue to the level of spinal injury. Initially, investigations usually consist of cervical spinal X-rays and then MRI. The spine is then immobilized and, if necessary, spinal realignment is obtained with traction. High-dose steroids can also be given. Surgical stabilization of the spine is then usually performed. Neurorehabilitation is important.

Postsurgical infection

Postcraniotomy wound infections occur in less than 1% of procedures and are generally due to staphylococcus. Once the flap is colonized and a nidus of osteomyelitis has developed, the infection will not usually be eradicated by antibiotic therapy. Quite frequently, a sinus will develop along the line of the craniotomy scar and intermittently discharge pus. In most cases, the flap needs to be removed and some form of cranioplastic procedure is performed 9–12 months later. Fortunately, infection of the brain itself following surgery is extremely rare, even following the implantation of prosthetic material.

Meningitis

Although most forms of meningitis are treated by physicians, some involve neurosurgeons. For example, a dural tear following a skull-base fracture leads to the egress of CSF into the paranasal sinuses (cranionasal fistula) or mastoid air cells. From there, the CSF can pass through the Eustachian tube into the nasopharynx (cranioaural fistula). Under these circumstances, pneumococcal infection can occur, either early or extremely late following injury. Early treatment of post-CSF fistula meningitis is important, as this generally leads to a very satisfactory outcome. Conversely, failure to recognize the disorder can result in death. With post-traumatic CSF fistula, there is no evidence that prophylactic antibiotics reduce the incidence of meningitis. If the CSF leak continues, then the site of leakage needs to be surgically repaired.

Gliomas

This group comprises the most common (60%) primary in-tracranial tumour. Gliomas arise from the brain-supporting cells. Glioma is a generic non-specific term applied to such diverse tumours as glioblastoma, astrocytoma, oligodendroglioma and ependymoma. These are infiltrating tumours and are graded using the WHO four-point scale:

Fig. 24.11 Coronal MRI scan showing a right temporal mass lesion of low signal intensity, with an oval-shaped region of gadolinium enhancement.

The latter suggests malignancy. This tumour was an anaplastic astrocytoma.

Meningiomas

These arise from the dura (Fig. 24.12) and account for 20% of all primary intracranial tumours. They commonly arise from the skull convexity, skull base or sagittal sinus region. They may compress the adjacent brain and cause seizures. They are generally slow-growing (90% are WHO grade I tumours) but may spread widely over the dura (‘en plaque’ tumours), and may invade the skull to form a palpable mass. The treatment is excision and prognosis is usually good. However, recurrences are not infrequent with WHO grade II (atypical) or WHO grade III (anaplastic) meningiomas, or following subtotal excision of a grade I tumour.

Fig. 24.12 Axial MRI showing a large sphenoid wing meningioma (arrow).

There is no associated brain oedema. This tumour caused troublesome seizures.

Schwannomas

Cranial nerve tumours account for 10% of intracranial tumours and virtually all of them affect the vestibulo-cochlear nerves (acoustic neuroma or vestibular schwannoma) (Fig. 24.13). The tumour grows within, expands and erodes the internal auditory meatus. The VIIth and VIIIth nerves become stretched over its surface as it grows into the cerebellopontine angle. Early VIIIth nerve symptoms include progressive nerve deafness, tinnitus and vertigo. Larger tumours may involve the trigeminal nerve, leading to diminished facial sensation, as well as the pons and cerebellum, leading to ataxia and nystagmus. Displacement of the fourth ventricle and aqueduct may lead to hydrocephalus. Patients are often misdiagnosed as having Ménière’s disease and the tumour may reach a large size before it is discovered. Treatment options include microsurgical excision, stereotactic radiosurgery or observation.

Fig. 24.13 Right acoustic neuroma.

Pituitary tumours

These account for 10% of all intracranial tumours. Histologically, most are benign. They produce symptoms through local pressure on the visual apparatus (e.g. distortion of the optic chiasma leads to bitemporal hemianopia) and endocrine effects (by secretion of hormones). They may be treated medically, by trans-sphenoidal hypophysectomy and by radiotherapy.

Brain metastasis

Metastatic tumours are present at postmortem in 20% of patients dying of cancer, and in 50% they are multiple (Fig. 24.14). They most commonly arise from the lung, breast, kidney, melanoma and colon. Such metastases may be the presenting feature or appear only late in the course of a previously diagnosed primary cancer. Prostate cancer classically spreads to the cranium and never involves the brain parenchyma. Conversely, gliomas very rarely spread beyond the central nervous system.

Fig. 24.14 Coronal MRI scans showing two gadolinium-enhancing lesions in the brain.

A The smaller lesion is in the cingulate region of the cerebral hemisphere. B The larger lesion is in the cerebellum. Both have low signal intensity centres, suggesting necrosis. The multiplicity of the lesions is highly suggestive of metastatic neoplasia. This MRI appearance can also be seen with multiple brain abscesses.

Clinical features of intracranial tumours

Diagnosis

MRI of the brain parenchyma, before and after the administration of contrast agents, usually clarifies the locality and neuropathology of neoplastic cranial lesions. In most malignant tumours, there is a neovascular capillary bed so that with anaplastic change, tumours will enhance (see Fig. 24.11). However, some low-grade tumours (e.g. pilocytic astrocytomas) also enhance, even though these are, in fact, grade I tumours. Meningiomas, which have a mesodermal origin, do not have a BBB and therefore enhance. With the better resolution of MRI, apparently solitary lesions on CT are not infrequently found to be multifocal. A feature of the anaplastic and malignant tumours is peritumoral brain oedema. This fluid occurs in the interstitial white matter due to the neoplastic endothelium not having the integrity of the normal BBB.

Management

The management principles of surgical neuro-oncology generally rely on:

The groups of operations that can be performed for brain tumours generally include biopsy, craniotomy and tumour resection. A range of surgical adjuncts, such as awake craniotomy and intraoperative localization techniques, are now employed. The surgical procedure to be undertaken is influenced by the neuroradiological findings (i.e. the likely tumour pathology) and the patient’s age, symptomatology and functional status, as well as the accessibility and multiplicity of the lesional pathology.

If peritumoral brain oedema is a feature, the administration of dexamethasone can lead to a dramatic reduction in symptoms and signs over a 12–24-hour period. How steroids work in brain tumours is not well understood, but their preoperative use has led to a major reduction in surgical morbidity and mortality. If the clinical and radiological parameters suggest only diagnosis is required, then stereotactic or image-guided frameless biopsy is the procedure of choice. This relatively simple procedure involves obtaining special CT or MRI images, entering this detailed information into a computer and then performing the biopsy. Surgery requires a 2.5 cm incision in the head, drilling a burr hole and either affixing a stereotactic frame to the cranium or using a computer image-directed biopsy system. The settings are adjusted so that the biopsy needle is directed at the chosen tumour target. Such systems are accurate to within 1 mm and the tumour diagnostic rate is around 98%. Because this is a minimally invasive procedure, the associated morbidity is generally very low (around 5%) and the 30-day mortality is usually less than 2%. Much of the latter is, however, related to the primary disease process rather than direct complications of the surgery.

Excision of the lesion is warranted to reduce mass effect, control seizures and restore lost brain function. If the preoperative neuroradiology suggests a malignant glioma, then extensive resection may provide optimal symptomatic control, a smoother course during radiotherapy and a reduction in steroid requirement. A recent phase III study has shown survival benefit for patients with malignant gliomas who have had nitrosurea-impregnated biodegradable wafers (Gliadel) placed in the resection cavity (EBM 24.6). If the lesion is a meningioma, then a total excision is generally planned, as this is a benign lesion. Similarly, if a posterior fossa lesion looks like a vestibular schwannoma, complete excision may be the treatment of choice. During excisional surgery, a whole variety of adjunctive techniques can be used, ranging from surgical ultrasonic aspirators to intraoperative localization techniques, as well as cortical stimulation of the brain of the awake patient with neurophysiological assessment. The latter technique is extremely useful in operating in areas of eloquent brain, such as the language cortex and motor region.

Outcome after surgical resection is influenced by many factors but, for malignant gliomas, the 30-day mortality is around 5% and neurological morbidity around 10%. Common complications include iatrogenic neurological deficits, cavity and extradural haematomas, and superficial wound infections. Outcome for primary intracranial tumours depends largely on tumour type (see above). Outcome following surgical excision of brain metastases depends on the state of the primary disease, as well as the locality and multiplicity of intracranial disease. Excision plus radiotherapy of a solitary metastasis is typically associated with a median survival of 7 months.

Aetiology and clinical features

Hydrocephalus is the accumulation of CSF within the ventricles or over the surface of the brain. This may rarely be due to overproduction of CSF (because of a choroid plexus papilloma), but the vast majority are due to reduced drainage secondary to obstruction of normal CSF flow (Fig. 24.17). Obstruction may be congenital, such as in aqueduct stenosis (Fig. 24.18), or acquired, as a result of tumour or arachnoidal adhesions and fibrosis secondary to intraventricular or subarachnoid haemorrhage. Hydrocephalus due to obstruction of flow within the ventricular system, leading to dilatation of the ventricles, is termed ‘internal’, ‘non-communicating’ or ‘obstructive’. In ‘external’ or ‘communicating’ hydrocephalus, the ventricular system is patent but there is reduced flow through the basal cisterns or absorption of CSF by the arachnoid granulations. This is commonly due to fibrosis following meningitis or subarachnoid haemorrhage, or to sagittal sinus thrombosis. In this type, the ventricles and the CSF spaces around the surface of the brain will be enlarged. In adults, chronic hydrocephalus may cause the ‘normal pressure hydrocephalus’ syndrome of gait ataxia, incontinence and cognitive decline. Diagnosis is often difficult in the elderly because brain atrophy causes ex-vacuo dilatation of the ventricles due to loss of brain substance, mimicking hydrocephalus. Cognitive decline can be asso ciated with Alzheimer-like pathology or cerebrovascular disease, and urinary disturbances may be related to prostate problems.

Fig. 24.17 Hydrocephalus: sites of cerebrospinal fluid (CSF) blockage.

Fig. 24.18 MRI of aqueduct stenosis (arrow 1).

This is an example of an obstructive hydrocephalus. There is gross ventricular enlargement (arrow 2) and herniation of the floor of the third ventricle into the interpeduncular cistern (arrow 3).

Congenital hydrocephalus usually presents at birth or in early infancy. The cranial sutures may start to open and the fontanelle will be tense and bulging. The veins of the scalp and the bridge of the nose will be dilated. As the hydrocephalus worsens, the eyes may become downcast (sunsetting). The child may be floppy and develop apnoeic spells and episodes of bradycardia. In older children and children with closed fontanelles, the symptoms are those of raised ICP (headache, vomiting and drowsiness). The eyes may develop a squint owing to VIth cranial nerve palsy. Papilloedema may be present and, if severe or chronic, may lead to blindness.

Management and prognosis

Treatment consists of relieving the pressure by bypassing the block to CSF drainage. In some cases of aqueduct stenosis, this can be done in a minimally invasive way by endoscopic third ventriculostomy. In this procedure, using an endoscope a small hole is formed in the floor of the third ventricle, allowing CSF to flow into the basal cisterns. In most cases, however, a ventriculo-peritoneal (VP) shunt will have to be inserted (Fig. 24.19). This consists of a catheter in the lateral ventricle, which drains CSF through a valve (that sits on the skull under the scalp) into the peritoneal cavity. The risk of bleeding into the ventricular system or brain during the insertion or removal of a VP shunt is of the order of 1–2%. There is also a risk of early infection, usually with skin commensal organisms such as Staphylococcus epidermidis. Shunts can become blocked or malfunction, causing a rapid return of symptoms, and this can be a medical emergency. Shunts can also become infected many months or years after insertion, in which case the shunt has to be removed and reinserted once the infection has cleared. Occasionally, a shunt will over-drain the ventricles, leading to premature closure of the cranial sutures and microcephaly. Over-drainage may be symptomatic, with headache and vomiting. It also predisposes to blockage of the ventricular catheter.

Fig. 24.19 Hydrocephalus.

A CT showing adult hydrocephalus. B MRI after operation (ventriculo-peritoneal shunt, arrow). There has been dramatic resolution of the hydrocephalus.

The long-term prognosis depends very much on the underlying cause of the hydrocephalus. In cases of simple aqueduct stenosis treated early, the prognosis for normal IQ and normal neurological function is good. Repeated episodes of raised ICP or ventriculitis can lead to loss of IQ and neurological deficit.

Aetiology and clinical features

Degenerative changes in the intervertebral discs and reactive changes in the vertebral bones are common in the lumbar and cervical regions. Disc degeneration is associated with loss of ‘disc space’ height. This throws abnormal strain on the intervertebral (apophyseal) joints, leading to osteophyte formation and narrowing of the intervertebral foramina. This condition is known as spondylosis and is associated with chronic disc herniation; it may lead to nerve root (lateral recess stenosis), cord (spondylitic myelopathy) or cauda equina (lumbar canal stenosis) compression. These may result in a radiculopathic (i.e. a specific nerve root syndrome), myelopathic or lumbar claudication-type syndrome, with or without low back or neck pain.

In response to acute trauma, the nucleus pulposus may protrude (herniate) through a tear in annulus (Fig. 24.21). Posterolateral protrusion usually compresses the adjacent nerve root or radicle, causing a sciatica (lumbar) or brachialgic (cervical) syndrome, with or without neurological deficit. Leg pain may be exacerbated by coughing and sneezing, and arm pain by neck movement. There is usually loss of normal lumbar lordosis, and a scoliosis often develops that is concave to the affected side. Straight leg raising is diminished. The neck may have paravertebral spasm. Tendon jerks and muscle power are diminished according to the site of the lesion Thus a L5/S1 prolapse affects the S1 nerve root and produces pain down the back of the thigh, the lateral side of the calf and the lateral border of the foot. There is sensory loss in the latter region. The ankle jerk may be diminished or absent and, as plantar flexion of the ankle is weak, the patient may have difficulty standing on tiptoe. With an L4/L5 disc prolapse, the L5 root is compressed. Pain radiates down the back of the thigh, the lateral aspect of the calf and the dorsum of the foot into the great toe. There may be accompanying sensory loss; the ankle jerk is normal but ankle dorsiflexion is weak.

Fig. 24.21 Sagittal MRI scan of the lumbar spine showing bulging and herniation of the L4/5 disc (arrows).

A surgical emergency occurs if the disc prolapses or herniates directly into the spinal canal (Fig. 24.22). In the cervical region, this will cause a progressive myelopathy, with numb, clumsy hands and spasticity. In the lumbar region, it is usually associated with severe pain in both lower limbs, loss of foot function, urinary retention and numbness up the back of the legs and around the genitalia, anus and buttocks (saddle anaesthesia). A rectal examination should be performed to assess anal tone. These features, known as a cauda equina syndrome, may be unilateral if the disc prolapse is asymmetrical.

Fig. 24.22 MRI of the cervical spine.

A The sagittal image shows severe spinal cord compression by a central disc prolapse (arrow). B Axial image showing the spinal canal, cord and CSF (arrow) at a normal level. C Axial image at the level of compression. The posterior disc herniation (arrow) is easily seen.

Management

Degenerative lumbar and cervical spine problems are extremely common, but the majority of problems respond to analgesia, physiotherapy and acupuncture. About 90% of cases of acute sciatic pain will settle with conservative treatment within three months. Persistent pain associated with signs of neural compression may require surgical decompression. The investigation of choice is spinal MRI. Flexion and extension X-rays may occasionally be useful if there is a spondylolisthesis and any question of spinal instability contributing to the clinical syndrome but X-rays are not indicated in uncomplicated cases of back pain or sciatica. In some cases, unusual pathology, such as metastatic tumours, neurofibromas and spinal ependymomas or meningiomas are the cause of pain or neurological disability.

The type of surgery is determined by the clinical syndrome and radiological investigations. A microdiscectomy may be performed for a simple posterolateral disc prolapse causing a sciatica-radicular syndrome. A posterior foramenotomy or anterior cervical discectomy, with or without fusion and plating, may be performed for a cervical disc prolapse. For multiple-level spinal canal stenosis, a laminectomy may be required in either the cervical or lumbar region. For lumbar spondylolisthesis associated with canal stenosis or radicular signs, decompression and fusion with pedicle screws for stabilization may be necessary. Results depend on many parameters.