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Adequately treated fibrosarcomas have a 5-year survival rate of 77%.

Rhabdomyosarcoma arises from skeletal muscle and occurs in both a juvenile and an adult form.

Embryonal rhabdomyosarcoma usually occurs in children younger than 15 years of age.

The head, neck, and genitourinary system are most frequently involved.

This tumor has recently enjoyed a spectacular increase in the 5-year survival rate. The combination of surgery, radiotherapy, and multidrug chemotherapy now achieves a 70% 5-year survival rate for patients with isolated lesions. If metastases are present, the survival rate is lower but is still approximately 40%.

Pleomorphic rhabdomyosarcoma is the histologic type that is usually found in adults.

Wide excision (including amputation, if necessary) is the treatment of choice. Chemotherapy is much less effective in this form of the tumor.

Although lymph node dissections are not done in most cases of sarcoma, they should be done for pleomorphic rhabdomyosarcoma because 25% of patients have regional nodal metastasis.

The 5-year survival rate is 30%.

Kaposi's sarcoma , which has attracted attention recently in connection with acquired immunodeficiency syndrome (AIDS), is a malignant lesion of vascular origin.

Until recently, it was usually seen in the lower extremities of older men. Now, it is often seen in the perianal area in connection with AIDS.

It usually begins as a single bluish -red macule, and gradually, multiple nodules appear and may ulcerate.

A solitary nodule should be excised, and widespread disease should be treated with radiotherapy. Although there is no cure for systemic Kaposi's sarcoma, patients may live for many years.

Lymphangiosarcoma is a peculiar tumor that develops in areas of chronic lymphedema (e.g., in the arm of women with postmastectomy edema, particularly if radiotherapy has also been used). The prognosis is dismal, and there is no effective treatment.

Benign sarcomas

Desmoid tumors are classified as benign fibromatoses that have the capacity to grow to a large size with a high rate of recurrence after excision. They are associated with Gardner's syndrome. They usually affect the shoulder and trunk and may affect the abdominal wall in parous women.

Dermatofibrosarcoma protuberans is a slow -growing nodular tumor with a high recurrence rate after excision. Histologically, it exhibits a “cartwheel” pattern of fibroblasts.

Paraganglioma (chemodectoma, carotid body tumor) presents as a painless mass in the neck overlying the carotid bifurcation. Most tumors are benign. Excision is curative.

Chapter 27

Neurosurgery

Allan J. Hamilton

Martin Weinand

I Introduction

Neurosurgery is surgical management of nervous system disease. The 1990s have seen rapid expansion and application of innovative technologies, including magnetic resonance imaging (MRI) and angiography for detecting lesions of the brain and spinal cord; positron emission tomography (PET) for evaluation of metabolic defects in the brain; and minimally invasive techniques such as implantable deep brain stimulators, interventional radiology for aneurysms, and radiosurgery. There have also been refinements of operative tools, including the computed/imageguided neuronavigation operating microscope, the ultrasonic aspirator, and the laser.

II Anatomy

The brain accounts for only 2% of the body weight but requires 18% of the cardiac output and 20% of the oxygen used by the body. The normal cerebral blood flow is about 50 mL/100 g of brain tissue per minute.

A Arterial supply to the brain

The anterior circulation is derived from the two internal carotid arteries , giving rise to the middle cerebral and the smaller anterior cerebral arteries. These vessels supply mainly the frontal, temporal, and parietal lobes as well as the deep gray matter.

The posterior circulation is comprised of the two vertebral arteries.

At the caudal margin of the pons, the arteries unite to form the basilar artery.

The basilar artery gives off branches supplying the pons, cerebellum, thalamus, and dividing into the posterior cerebral arteries, it supplies the occipital lobes.

The circle of Willis , an arterial circle, is formed by communicating arteries between the major branches of the anterior and posterior circulations. In the event of a trunk vessel occlusion, the blood supply to its territory may be supplied by another vessel via the circle of Willis.

B Venous return to the brain

Superficial cerebral veins drain the cortex and subcortical white matter and drain into the superior sagittal sinus or the basal sinuses (i.e., the transverse, petrosal, or cavernous sinuses).

Deep cerebral veins drain the deeper structures (nuclei). The deep veins consist of the paired internal cerebral and basal (Rosenthal) veins, which form the great vein of Galen before emptying into the straight sinus.

All venous blood from the brain returns to the heart via the internal jugular veins.

Sampling of blood from the jugular bulb provides an estimate of cerebral metabolism.

C Arterial supply to the spinal cord

The spinal cord is supplied by the anterior spinal artery and the paired posterior spinal arteries , reinforced by the segmental radicular arteries.

The anterior spinal artery branches into the anterior sulcal artery in the anterior sulcus, which supplies the anteromedial gray matter.

The segmental arteries are important because their interruption can lead to infarction of the spinal cord.

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D

Venous return from the spinal cord parallels the arterial supply.

Anterior longitudinal venous trunks drain corresponding areas of the cord and are drained, in turn, by 6– 11 radicular veins into the epidural venous plexus.

Posterior longitudinal venous trunks drain the posterior funiculus, the posterior horns, and the white matter in the lateral funiculi. These trunks, in turn, are drained by 5–10 radicular veins into the epidural venous plexus.

The epidural venous plexus is located between the vertebral periosteum and the dura mater.

The plexus consists of two or more anterior and posterior longitudinal veins interconnected at various levels.

At each intervertebral space, there is an extensive anastomosis with intercostal, thoracic, and abdominal veins.

None of these venous channels has valves, and thus, blood from these plexuses may directly enter the systemic circulation and vice versa.

E

Cerebrospinal fluid (CSF) brain tissue, and blood are the major components of the intracranial space.

Normally, the total volume of the CSF is about 150 mL, with 25 mL located in the ventricles. The CSF is formed at a rate of 0.35 mL/minute (approximately 150 mL three times per day). Roughly 80% of the CSF is produced by the choroid plexus, and the rest is secreted in the interstitial spaces of the brain.

The CSF flows from the lateral ventricles to the third ventricle through the foramina of Monro and reaches the fourth ventricle via the aqueduct of Sylvius and reaches the brain exterior by the foramina of Magendie (midline) and Luschka (lateral).

The CSF circulates around the spinal cord and the brain and is reabsorbed into the superior sagittal sinus via the arachnoid villi. Some of the CSF is absorbed around the spinal nerve roots.

The arachnoid villi act as one -way valves, and they open at a pressure of 5 mm Hg.

F Functional anatomy of the nervous system

The following principles form the basis for evaluating and treating neurologic disease.

Pathophysiologic processes unique to the nervous system result from the:

Complexity of the functional organization of the nervous system

Rigidity of the bony enclosures of the brain and spinal cord

Responses of the nervous system to injury

Focal lesions affect neurologic function by:

Local destruction of brain tissue

Tissue distortion with functional loss attributable to axonal stretching and subsequent synaptic damage

Changes in local blood flow, causing ischemia or venous congestion

Alterations in the electrical or metabolic activity of a local area, producing an epileptic focus

Location of the lesion

A small focal lesion in the brain stem can produce devastating effects.

A similar lesion in the frontal (silent) area may produce no significant neurologic deficit.

III Pathophysiology

A Cerebral edema

The brain reacts to insults by developing edema. Acute edema causes more deterioration in neurologic function than does chronic edema. The rate of edema formation is directly proportional to the neurologic deficits.

Types of cerebral edema

Cytotoxic edema is a result of depletion of neuronal glucose and oxygen stores. It is most commonly seen after cerebral infarction and may occur in association with Reye's syndrome. The blood–brain barrier is preserved.

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Vasogenic edema (also called extracellular white matter edema) results from a breakdown of the blood–brain barrier and leakage of plasma into the extracellular spaces. This is the most common type of edema seen clinically and may be caused by trauma, brain tumor, infection, surgery, and systemic hypertonicity, such as that due to use of mannitol.

Mechanisms by which edema alters neuronal and axonal function include:

Ischemia that occurs as increased intracranial pressure (ICP) compromises cerebral perfusion

Decreased oxygen diffusion

Lipid peroxidation in membranes

B ICP

The skull , a rigid box with a volume of approximately 1900 mL, harbors three major components:

Approximately 85% is brain (5% is extracellular fluid, 45% is glial tissue, and 35% is neuronal tissue).

Approximately 7% is blood.

Approximately 7% is CSF.

Monro-Kellie hypothesis. Under normal conditions, these three components and the intracranial volume are in equilibrium, yielding normal ICP.

To maintain a normal ICP, a change in one component must be offset by compensatory changes in

fluid.

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Vomiting

Clouding of mentation

Papilledema

Paralysis of upward gaze (Parinaud's syndrome)

Sixth nerve palsy

Bulging fontanelles and splitting sutures (in infants)

Measurement of ICP

In clinical practice, ICP may be measured by ventriculostomy, intraparenchymal monitoring device, or subarachnoid bolt.

An estimate of ICP may also be made by lumbar puncture in the absence of space -occupying intracranial lesions.

Whereas intraparenchymal and subarachnoid bolt monitoring produce continuous ICP data, ventriculostomy monitoring produces both a continuous record of ICP and the therapeutic option of removing CSF to reduce ICP.

C Herniation

When all compensatory mechanisms have been exhausted and the ICP continues to increase, the brain “herniates” or shifts toward the low -pressure compartment (the falx and the tentorium divide the interior of the skull into compartments). Various herniation syndromes are recognized.

Subfalcine herniation is a displacement from one supratentorial compartment to another underneath the falx. It may lead to loss of function in the opposite leg, loss of bladder control, or both.

Transtentorial (uncal) herniation

This is the most common type of brain herniation seen clinically and occurs when the medial temporal lobe of one or both hemispheres is forced down over the edge of the tentorium.

Uncal herniation may occur as a result of diffuse brain swelling or of a supratentorial mass lesion.

Neurologic signs are:

Progressive deterioration of consciousness

Ipsilateral pupillary dilatation from oculomotor nerve compression by the herniating gyri

Contralateral hemiparesis as a result of compression of the cerebral peduncles

Hemiparesis is ipsilateral in 50% of the cases, whereas pupillary dilatation is ipsilateral in 80%.