Central Herniated Disc

Clinical Vignette

A 68-year-old, part-time musician suddenly fell as he was reaching for his morning newspaper while standing on an icy, hilly driveway. He was paralyzed from his neck down, and he noted numbness in all extremities. He recalled a brief involuntary ballistic movement of his right arm. A diagnosis of a brainstem stroke was made at the local hospital as it was presumed that the stroke led to his fall. Brain computed tomography (CT) was normal. Within a few days, he recovered some right-sided motor function.

The family sought a second opinion at Lahey Clinic. Here he had a left > right quadriparesis, bilaterally brisk muscle stretch reflexes, left Babinski sign, and a midcervical right-sided sensory level for pain and temperature with preserved position sense, an exaggerated Brown–Sequard syndrome. MRI demonstrated a centrally herniated nucleus pulposus at C3–C4 with spinal cord compression, contusion, and a severe stenotic spondylotic lesion at that level. Emergency surgical decompression was performed. He had a gradual increase in function; within 1 year he could perform most activities of daily living independently, although his finger dexterity for clarinet playing was not back to his preinjury level.

In retrospect, he had sustained a syncopal event secondary to a cardiac arrhythmia. The fall per se led to the spinal column injury, the extruded central disc and cord injury. A careful neurologic examination sorted out the site of pathology and led to the diagnostic and therapeutic triumph!

Comment: Initially, this patient was thought to have a basically untreatable brainstem stroke, that is, a lesion in an entirely different part of the neuraxis. A more careful subsequent clinical examination, lying the patient on his side and examining for a specific sensory level, was the key to diagnosis, as patients with brainstem stroke rarely have total loss of sensory function in a spinal cord–level distribution (see Figs. 44-11 and 44-12).

Acute spinal cord injuries, with subsequent paraplegia or quadriplegia, are among the most dreaded sequelae to a serious bodily injury (Box 45-1). There is a tragic propensity for traumatic myelopathies to occur among vigorous and healthy young persons. Automobile and motorcycle accidents as well as sports injuries are the most common etiologies. Gunshot wounds, whether resulting from war, accident, or assault, are another source of traumatic spinal cord injury.

Box 45-1 Acute Extradural Extramedullary Myelopathies

• Trauma

• Metastatic bone tumors with secondary invasion of the epidural space:

• Breast

• Lung

• Prostate

• Kidney

• Colon

• Thyroid

• Myeloma

• Plasmacytoma

• Lymphoma

• Epidural abscess with disc space infection

• Disc herniation affecting central cord

• Arteriovenous malformation

• Hematoma epidural,

• Subdural hematoma as acute intradural extramedullary

Cervical spinal fracture dislocation with resultant ligamentous tear, allowing bony fragments to directly tear or transect the spinal cord, is the common denominator in this setting (Fig. 45-2). Sometimes, there is concomitant compromise of the spinal arteries causing an associated spinal cord infarction, hematomyelia, or both. Typically, in the acute setting, spinal shock results with complete paralysis, loss of sensation, areflexia distal to the trauma site, and loss of bladder and bowel function.

Figure 45-2 Trauma.

Occasionally, these traumatic spinal lesions are amenable to immediate surgical correction or external traction (Chapter 60). Prognosis is always guarded. Once emergent management is completed, these patients are cared for at specialized spinal rehabilitation centers. Treatment of autonomic and sphincter dysfunction has greatly improved the long-term survival for many patients. Spinal cord repair, leading to functional recovery, is one of the greatest challenges for 21st-century neuroscientists.

Among senior citizens, unexpected falls at home, as in the above vignette, may lead to an acute central disc protrusion. Their inherent gait instability secondary to chronic neurologic or orthopedic handicaps make them susceptible to tripping on stairs, rugs, or door jams. Cardiac bradyarrhythmias leading to syncope, or epileptic seizure, with sudden loss of consciousness have a similar risk of serious spinal cord injury.

As these lesions are eminently treatable with neurosurgical intervention, consideration of these less common lesions is vital in patients who have sudden unexplained falls leading to immediate paralysis. Anatomically, the extruded disc compressed the anterior spinal cord between two vertebral bodies. Occasionally, these lesions present subacutely or chronically. Because associated bony pain or tenderness may be present, these lesions often mimic metastatic or primary tumors. However, if the patient does not have a history of malignancy, a benign mechanism, such as a central disc, must be sought (Figs. 45-3 and 45-4). Rarely, a dural arteriovenous malformation (AVM) or spinal epidural hematoma (SEH) mimics this clinical picture.

Figure 45-3 Cervical Disc Herniation.

Figure 45-4 Idiopathic Spinal Stenosis.

Surgery is the treatment of choice. Prognosis depends on the degree of cord compromise before surgery, the acuity of the event, the patient’s general health status, and the disc location. Cervical lesions are treated by a neurosurgeon, although a combined approach with an orthopedic surgeon is sometimes indicated. When the central disc is in the thoracic cord area, a combined neurologic and thoracic surgical approach is required.

Clinical Vignette

A 60-year-old man with diabetes and a recent history of dental extractions developed lumbar and soon thereafter thoracic spine pain. During the next 2 days, his pain worsened even while lying in bed. Neither meperidine, a narcotic agent, nor a muscle relaxant relieved his pain and paraspinal muscle spasm. His difficulties rapidly worsened as he began to have trouble walking, lost sensation in his legs, and became unable to urinate.

Neurologic examination demonstrated an acutely ill febrile individual with a flaccid paraplegia, brisk muscle stretch reflexes at the knees, bilateral Babinski signs, loss of position sense in the feet and a cord level to both pin and temperature sensation at T6. There was percussion tenderness over his upper thoracic spinous processes. MRI demonstrated an extensive epidural collection extending from C6 to T10. Emergency laminectomy was performed, which demonstrated a purulent epidural abscess. Despite the emergent surgery, the patient was still significantly limited a few months later.

Epidural spinal abscess is a rare clinical process occurring in 2–20 cases per 100,000 hospital admissions. Its incidence appears to be increasing; these are usually seen in middle-aged adults, more often men. Despite its rarity, the potential for an epidural abscess to cause permanent paraplegia makes it one of the most urgent spinal cord emergencies (Fig. 45-6). Even though back pain is such a ubiquitous and usually benign process, it is very important for any physician to consider the potential diagnosis of an epidural abscess in every patient presenting with acute and increasing back pain, especially when febrile. The epidural space in the posterior thoracic cord is the primary site for an epidural spinal abscess to develop. These may extend to the cervical cord and rarely into the lumbar spine. Experimental studies suggest that the mass effect of the abscess, leading to cord compression, is the important clinicopathologic mechanism.

Figure 45-6 Epidural Abscess and Epidural Hematoma.

Staphylococcus aureus is the predominant etiologic microorganism leading to epidural spinal abscesses. Usually a distant septic focus provides bacterial seeding via the bloodstream, for example, skin furuncles, dental abscesses, simple pharyngitis, or a recently infected traumatic site (see Fig. 45-6). Often there is a concomitant history of diabetes mellitus, alcoholism, drug abuse, or recent spinal or extraspinal trauma. Less commonly, epidural spinal abscesses develop subsequent to vertebral osteomyelitis, pulmonary or urinary infection, sepsis, or extremely rarely bacterial endocarditis. Invasive procedures, including epidural anesthesia, spinal surgery, vascular access lines, and paravertebral injections, also provide potential mechanisms for bacterial seeding. Corticosteroid therapy may contribute to immune suppression and the possibility of secondary nosocomial infections.

Percussion tenderness over the posterior spinal processes, as well as fever, are important diagnostic clues compatible with an epidural spinal abscess Some of these individuals also develop signs of meningeal irritation such as Kernig’s sign. A rapidly developing combination of motor, sensory, and sphincter dysfunction then occurs. Often the patient becomes paraplegic and demonstrates a spinal cord sensory level. The differential diagnosis includes acute central disc, epidural metastasis often with acute pathologic fracture, and spontaneous or anticoagulation-induced hematoma.

An urgent MRI easily identifies the epidural abscess. Concomitantly, there may be a highly elevated C-reactive protein and erythrocyte sedimentation rate, often >70 mm/hour, with a modestly elevated WBC count. Emergency surgical decompression is the treatment of choice. Occasionally when no significant neurologic compromise exists, antibiotics are the primary treatment. However, careful follow-up is indicated as the patient’s clinical picture may rapidly evolve with motor and sensory loss leading to need for another MRI and surgical intervention.

Prognosis depends entirely on the patient’s expeditious presentation to a medical facility and the clinician’s level of suspicion leading to relatively early diagnosis of the epidural spinal abscess. If treatment is not initiated until after the patient becomes paraplegic, prognosis is extremely guarded.

Clinical Vignette

Right arm weakness acutely developed in a 30-year-old woman. In retrospect, she had noted some numbness in that arm for the past 3 months, and 16 months earlier she experienced blurred vision in her right eye, with intermittent dizziness. She also had experienced episodic momentary electric shock, lightning-like sensation radiating to her buttocks often precipitated by bending her neck. Hot weather was more uncomfortable for her as she reported worsening of these symptoms and nonspecific fatigue. She had a slightly spastic left-sided gait, increased muscle stretch reflexes with a left Babinski sign, poor left-side position sense, and reduced pin and temperature sensation over her right arm and thigh.

Cervical spine MRI demonstrated an area of increased signal with ill-defined enhancement located posteriorly and on the left side of the cord (Fig. 45-7A). Brain MRI with and without gadolinium demonstrated a few periventricular lesions and other abnormalities oriented perpendicularly along vessels (Dawson fingers) within the corpus callosum. Visual evoked responses (VERs) were prolonged for her right eye. Her cerebrospinal fluid (CSF) was significant for 10 white blood cells (99% lymphocytes, 1% monocytes), and the presence of oligoclonal bands that was not identified in her serum.

Figure 45-7 Myelitis Secondary to Neuromyelitis Optica (Devic) and Multiple Sclerosis.

The brief sensation of an electric shock running out the arms or down the back when a patient bends their neck is known as the Lhermitte sign. It is a classic symptom of cervical spinal cord posterior column pathology. Although most commonly seen in MS, because of the high incidence of this disorder, it is a non-specific symptom that is also seen in other intramedullary lesions such as vitamin B₁₂ deficiency, or a number of extramedullary lesions causing cord compression.

Comment: This vignette presents a classic clinical picture of early multiple sclerosis (MS). The patient has an incomplete demyelinating myelitis consistent with classic hemicord syndrome, affecting ipsilateral motor and proprioceptive function and crossed sensory fibers. This is known as the Brown–Sequard syndrome. However, she also had involvement of her right arm, implying extension into the right anterior horn. The presence of the subclinical brain MRI abnormalities, as well as the prolonged VERs, point to multiplicity of demyelinating lesions in time and space consistent with the diagnosis of MS (Table 45-1).

Table 45-1 Acute Intradural Intramedullary Myelopathies

Clinical Vignette

An obese septuagenarian, with previously diagnosed diabetic polyneuropathy manifested by burning discomfort in his feet, presented with a 4- to 6-month history of increasing leg numbness. These new symptoms were totally different from the mild tingling and burning that had been chronically present for the past 10 years. He began to require a cane to maintain his equilibrium when walking. Although he initially tolerated the newer symptoms, he began to be concerned that he could not walk safely without relying on a walker. He sought further medical opinion. He previously had a myocardial infarction.

Neurologic examination demonstrated a broad-based, spastic gait, brisk muscle stretch reflexes, and bilateral Babinski signs. Pinprick and temperature sensation were reduced in a stocking-glove distribution in his legs. There was a question of a bilateral cord level to pin sensation at C-7. Position sense was absent at the toes, and vibratory sense lost at the ankles.

MRI revealed spinal stenosis and cord edema at C5–C6. He had severe spinal stenosis with multilevel spondylosis, disc protrusion, and end-plate osteophytes. After a 3-month period of observation, his gait difficulties increased. A cervical posterior laminectomy was performed. Subsequently, after a period of rehabilitation hospitalization, he gradually regained the ability to walk independently.

One needs to always carefully evaluate the patient with a chronic primary sensory polyneuropathy who begins to develop disproportionately increased gait difficulty. Cervical spinal stenosis is a common chronic disorder. As occurred in this instance, one may define a quite remediable condition.

Spondylosis, a normal aging process, is the most common cause of a cervical myelopathy (Figs. 45-9 and 45-10; Box 45-2). This results from disc degeneration followed by reactive osteophyte formation, fibrocartilaginous bars, spondylotic transverse bars, articular facet hypertrophy, and thickening of the ligamentum flavum causing spinal canal narrowing. Subsequently, gradual spinal cord compression may occur; it is particularly likely in patients having congenitally narrowed spinal canals. In its simplest form, a chronically herniated central nucleus pulposus in patients with congenital stenosis can produce a cervical myelopathy. Although many senior individuals have radiographic signs of cervical spondylosis, most are asymptomatic. When a myelopathy develops, clinical findings can present acutely, subacutely, or over many years. Sometimes both a cervical myelopathy and adjacent radiculopathy may occur in the same spondylotic patient.

Figure 45-9 Cervical Spondylosis.

Figure 45-10 Imaging of Ossification of Posterior Longitudinal Ligament (OPLL).

Pathophysiology and Etiology

Typically, the spinal canal is 17–18 mm in diameter between C3 and C7. A narrower cervical spinal canal may range from 9 to 15 mm; however, a compressive spondylitic myelopathy rarely occurs when the canal diameter is >13 mm. Cervical cord diameter ranges from 8.5 to 11.5 mm, averaging approximately 10 mm. Disc protrusion and other reactive and degenerative processes further reduce canal dimension. Direct cord compression, compromised blood supply to the cord or venous stasis, and other mechanical factors, such as rheumatoid arthritis, can in combination or independently cause irreversible damage.

Normally, the spinal cord moves cephalad and posteriorly within the canal during neck flexion and caudally and anteriorly during neck extension. If osteophytes, discs, and hypertrophied ligaments make contact with the cord, the cord sustains additive trauma, leading to development of a clinical myelopathy. The disc levels affected are C5–C6, C6–C7, and C3–C4, in order of their clinical frequency.

In this setting, the spinal cord may become pathologically, grossly flattened, distorted, or indented. Demyelination of the lateral columns occurs at the lesion site with consequent lateral column degeneration below the lesion. Concomitant dorsal column degeneration occurs at and above the damaged segment(s). There may also be damage and loss of nerve cells in gray matter. Ischemic changes, gliosis, demyelination, and even cavitation necrosis sometimes also result.

Clinical Presentation

The patient may initially note a tendency for his foot to drag or scuff on rugs or curbs. Limb paresthesias are generally relatively mild dysesthesiae often mimicking a polyneuropathy. As this disorder evolves with more significant cervical cord involvement, an increasingly severe proprioceptive loss occurs, often leading to a sensory ataxia. Examination demonstrates mild asymmetric spasticity with upper motor neuron corticospinal tract findings including hyperreflexia, and Babinski signs primarily related to lateral cord compression. Diminished position and/or vibration sense are markers of posterior column pressure. Bowel and bladder disturbances are usually late findings. If there is concomitant ventral cord compression, the anterior horn cells within the gray matter may be damaged, characterized by muscle fasciculations, atrophy, and weakness appropriate to the affected nerve roots.

Neck pain varies. Lhermitte’s sign may occur, characterized by recurrent lightning-like paresthesias traversing down the back with neck flexion. When the syndrome is purely spinal, a myelopathy without root signs or symptoms occurs. However, a radicular syndrome occasionally accompanies the myelopathy presenting with radicular pain, sensory or motor deficit, or both. This is localized to the area innervated by the specific nerve root.

The clinical course varies among patients. Although some individuals have a mild protracted insidious course, even over decades, others have subacute temporal profiles progressing over a few months to a relatively severe disability. Infrequently, these patients are prone to acute cord compression secondary to a fall, as the compromised spinal canal diameter makes it more likely that the cord will be contused with sudden hyperextension or flexion. This may even mimic a stroke, as noted in the initial vignette in this chapter. Here it is important to emphasize clinical evaluation for a cervical spinal sensory level as the important defining feature of an acute myelopathy.

Rarely, sudden neck hyperextension leads to a temporary “person in the barrel” syndrome. Here there is an acute compression of the anterior spinal cord. This transiently impairs the segmental anterior horn cells innervating the arm musculature. The clinical picture of isolated arm and hand weakness relates to the preserved lateral column corticospinal tract function; thus the legs are unaffected.

Clinical Vignette

A very unique scenario occurred in a 40-year-old man who, while skiing, noted that his ankles “vibrate” each time he “hit the bumps.” This advanced skiing technique involves rapidly traversing through and over these mounds of snow (moguls) that routinely pile up on steep ski trails. The skier negotiates a field of moguls repetitively coming across these bumps, and then “jumps,” making a 90-degree turn to land on his skies with significant force. Our patient had performed this action in an almost perfunctory fashion for a number of winters. However, he recently noted that each time he landed on the mogul his legs grossly vibrated, sometimes causing him to fall.

His examination demonstrated bilateral ankle clonus, and a left Babinski sign. The patient likened this feeling of clonus to his skiing experience. Cervical spinal cord MRI demonstrated disc extrusion primarily at the C5–C6 level along with abnormal intramedullary enhancement compatible with a severe spondylotic cervical myelopathy (see Figs. 45-9 and 45-10). In this instance, the patient’s vivid description of a most unusual complaint (“mogul clonus”) led to careful investigation and eventual surgery. Six months postoperatively, “skiing the bumps” no longer produced clonus. Most importantly, his risk of permanent spinal cord injury was greatly lessened if he were to subsequently sustain a severe fall.

Comment: Presumably, this patient’s jumps onto the snowfield moguls, while skiing, dorsiflexed his feet abruptly enough to elicit a spontaneous clonus by a mechanism essentially similar to that used by a neurologist routinely checking for clonus. The force of his body coming down on the hard packed snow induced the “vibration,” that is, mogul clonus. The basic pathophysiology identified by the MRI was a congenital, very tight cervical spinal stenosis.

Diagnosis

MS, amyotrophic lateral sclerosis, vitamin B₁₂ deficiency, human T cell leukemia/lymphotrophic virus type 1 (HTLV-I) myelopathy, adrenoleukodystrophy, syringomyelia, and spinal cord tumors need to be considered in the differential diagnosis of cervical spinal spondylosis with cord compression. The presence of hand or leg paresthesia, Lhermitte’s sign, prominent neck pain, or significant sensory loss provides historic and examination evidence to distinguish cervical spondylosis with myelopathy from motor neuron disease/amyotrophic lateral sclerosis.

MRI is the diagnostic procedure of choice. It provides longitudinal segmental views of the cord, dural space, and relationships to bony and ligamentous structures. CT/myelogram is an alternative when MRI is contraindicated because of cardiac pacemakers or severe claustrophobia. CT can provide additional information about the bony structure regarding the foramen, facets, and uncovertebral joints. Electromyography/nerve conduction can help identify concomitant peripheral nerve disease or nerve root compression when the differential diagnosis includes a process in the peripheral motor sensory unit.

Treatment

Epidemiologic data regarding the natural history of cervical spondylosis are lacking. In patients with mild deficits from cervical myelopathy, it is unclear whether surgical decompression is superior to conservative management. Some patients remain stable or improve without treatment. For patients with evolving symptoms and deficits, surgical decompression is the treatment of choice to arrest progression of the myelopathy. Functional recovery may not occur if the deficit is already severe, possibly because of chronic ischemic cord damage from spinal artery compression.

Surgical approaches include the posterior approach, which allows for generous decompressive laminectomies, and the anterior approach, which enables operation on bars and spurs anterior to the cord and fusion when instability or subluxation is present. Discectomy, corpectomy, laminectomy, and laminoplasty are other surgical options.

Significant variations exist in the degree of postsurgical clinical improvement. Duration and severity of the myelopathy before surgery are key determinants for clinical outcome. Cord atrophy, irreversible signal change within the cord on T2-weighted MRI (gliosis rather than cord edema), superimposed trauma, and advanced age are negative prognostic factors. Maintaining spinal stability and treating anterior compression improve outcome.

Clinical Vignette

During the past year, this very healthy 45-year-old neuropsychologist experienced intermittent lower extremity paresthesia and heaviness in her legs. On one occasion, she experienced the precipitous onset of severe difficulty walking. This lasted for a few hours, and then resolved. Two months later, she developed low back pain, constipation, and problems voiding. She had a second episode of inability to walk lasting for several hours.

On neurologic examination, her proximal leg muscles were significantly weak; distal leg and all muscles in her arms were normal. Pinprick sensation was reduced in a patchy distribution in both legs. Her gait was broad based and unsteady and she was unable to walk on her heels or toes. Muscle stretch reflexes were increased in both legs and a right Babinski sign was present.

MRI demonstrated a swollen conus with increased vasculature. A selective intercostal angiogram revealed a dural AVM with its feeder vessel nidus at T11 on the left, and not involving the artery of Adamkiewicz.

A T10–T11 laminectomy was performed to remove the AVM. Large arterialized vessels were found medial to the nerve roots filling the dorsal subarachnoid space. These epidural vessels and large feeders at T10–T11 were coagulated. The patient’s strength improved postprocedure, returning to normal within 1 year. Bladder dysfunction was minimal. She has had excellent long-term follow-up examinations.

Comment: Spinal AVMs are a group of vascular disorders that can cause acute, subacute, or chronic spinal cord dysfunction. Dural AVMs present in later adulthood and may be acquired. The most common type is the dural AVM (80–85%), although intradural AVMs, combination intradural and extradural AVMs, and cavernous angiomas (cavernous malformations) also occur. A high index of suspicion is needed so as not to miss the diagnosis in any patient with unexplained myelopathy. An associated venous hypertension or bleeding of these spinal AVMs leads to the intermittent and eventually progressive myelopathy. Complete spinal angiography with concomitant obliteration of the AVM is usually indicated.

Pathophysiology and Etiology

Dural AVMs primarily occur in the mid to lower thoracic and lumbar spine. Many dural AVMs are AV fistulas that essentially have a single hole in an artery connected to a vein (Fig. 45-11). Radicular or dural branches from the segmental arteries supply the AVM, usually within the dura of an intervertebral foramen. The AVM nidus is typically a low-flow shunt drained by a single vein that joins the coronal plexus on the dorsal cord surface. The coronal plexus is arterialized by the AVM fistula and becomes dilated, coiled, and elongated. Blood flow through this vessel is slower than normal and thus leads to venous congestion with increased venous pressure that is transmitted intramedullarly, reducing the arteriovenous pressure gradient within the cord. Cord perfusion decreases, leading to prolonged ischemia/hypoxia and a progressive myelopathy. The effects of hypoxia that are initially reversible later lead to an irreversible degenerative cord necrosis. The corticospinal tracts, lateral white matter, and dorsal columns are especially vulnerable.

Figure 45-11 Spinal Arteriovenous Malformations.

Intradural AVMs originate from intramedullary arteries arising from the anterior spinal artery. The nidus can be in the cord (intramedullary), in the pia on cord surface (extramedullary), or be a combination of intramedullary and extramedullary. These AVMs are high-pressure systems with rapid blood flow. These can contain arterial aneurysms that can spontaneously hemorrhage within the cord or into the subarachnoid space. Unlike dural AVMs, intradural AVMs occur throughout the length of the cord. These intradural AVMs affect younger patients than do the dural lesions. These may be of congenital origin. Recurrent subarachnoid and intramedullary hemorrhage are the primary pathophysiologic mechanisms.

Cavernous angiomas or malformations are rare, isolated or multiple lesions, more common in the cerebral hemispheres than in the cord. These low-flow lesions can spontaneously hemorrhage and are best shown by MRI (spinal arteriography is normal).

Clinical Presentation

Dural AVMs occur more commonly in men. Symptoms typically emerge after age 40, peaking at 50–70 years. The thoracolumbar (T6–L1) region is most frequently involved. Symptoms are gradual in onset and slowly progressive. Back or radicular pain is the most frequent presenting symptom. Patients often have a combination of upper and lower motor neuron findings with spasticity, weakness, fasciculations, atrophy, hyperreflexia, hyporeflexia, and Babinski signs. A variable degree of leg weakness can progress from abnormal stance or gait to needing an assistive walking device to wheelchair or bed dependence. Sensory dysfunction is manifested by impaired joint position, vibration, pain, and temperature sensation. A discrete or vague sensory level may sometimes be identified. Various degrees of bladder, bowel, and sexual dysfunction develop. Very rarely auscultation over the spine demonstrating a bruit can help diagnose a high-flow AVM. Certain activities or postures may precipitate or exacerbate symptoms. Dural AVMs rarely hemorrhage.

Intradural AVMs affect men and women more evenly. They present at an early age, usually <40 years, sometimes during childhood. The AVM nidus is distributed evenly along the cord from the foramen magnum to the conus medullaris. Early clinical findings usually result from an intramedullary or subarachnoid hemorrhage. Patients usually develop progressive weakness, numbness, and sphincter dysfunction. Because the intradural AVM may be located in the cervical spinal cord, both upper and lower extremities are sometimes affected. Recurrent hemorrhages leads to clinical deterioration.

Diagnosis

Entities in the differential include MS, spinal pseudoclaudication associated with spinal stenosis, disc disease, acute or chronic infection, tumor, syringomyelia, and subarachnoid hemorrhage. All these conditions can have acute or slowly progressive courses.

With dural AVMs, MRI demonstrates serpentine filling defects of reduced signal in the subarachnoid space corresponding to blood flow in the dilated, tortuous coronal venous plexus. Sometimes cord signal is increased from edema or venous congestion. Rarely an MRI will fail to demonstrate a dural AVM.

In contrast, intradural AVMs of the spinal cord may have low signal corresponding to an intradural AVM nidus. A target sign may be seen at the site of previous hemorrhage.

Myelography may demonstrate serpentine linear defects. However, this medium is less helpful in distinguishing intramedullary from extramedullary lesions. Selective spinal arteriography offers more precise information regarding AVM anatomy.

Treatment and Prognosis

Treatment depends on the location, size, source of arterial supply and site of the shunt. Surgical removal, endovascular embolization, or both are often helpful.

For dural AVMs, goals are to eliminate the dural nidus and interrupt the AV fistula between the nidus and coronal venous plexus, resolving the venous hypertension and congestion, subsequently improving the myelopathy. Elimination of the fistula/nidus at the intervertebral foramen can be curative. The dilated veins of the coronal plexus can remain; their removal can be damaging and unnecessary.

Intramedullary AVMs are often inoperable. Embolization can occlude feeding vessels and the nidus, reducing flow and allowing lesion thrombosis. Collateral spinal vascular supply is needed to prevent cord damage from the subsequent ischemia. If the treated vessels recanalize, reembolization may be required.

Early detection and treatment can improve gait disturbances, sometimes bladder dysfunction, and other myelopathy signs, especially if they are less severe. A previously progressive course can be arrested by surgery.

Clinical Vignette

A 64-year-old man, hospitalized for an acute myocardial infarction, was dyspneic, with worsening heart failure. He complained of weakness and inability to ambulate. Additional medical history included obstructive pulmonary disease and low back pain, for which he received chronic intermittent steroids, including epidural injections.

Neurologic examination demonstrated significant iliopsoas weakness and no movement of his left foot. Muscle stretch reflexes were brisk with a right Babinski sign. Vibratory sensation was absent in lower extremities. There was no sensory level to pinprick. His thoracic spine was tender to palpation. Rectal tone was decreased. Within 5 days, his legs became plegic.

The patient was febrile. Sputum and blood cultures grew pseudomonas. A pacemaker precluded MRI. CT/myelogram demonstrated an epidural process extending dorsally T4–T10, and severe stenosis especially at T8 and T9. The spinal cord was displaced anteriorly with marked compression. The patient was taken to surgery for decompression and possible abscess drainage. Epidural lipomatosis was diagnosed.

Epidural lipomatosis is defined as excess adipose tissue deposition posterior to the spinal cord. Rarely described in children, it occurs primarily in a thoracic (61%), sometimes lumbar (39%) distribution, but not within the cervical spine. Men are affected more than women with average age 44, range 18–64 years.

Pathophysiology and Etiology

Epidural fat accumulation leads to cord compression with corticospinal tract and dorsal column compromise. Venous thrombosis can be a significant part of the pathology.

Epidural lipomatosis is sometimes a rare consequence of therapeutic corticosteroids, that is, part of an iatrogenic Cushing syndrome. The correlation between duration and dosage of steroid treatment is unknown. It can occur with prednisone dosages ranging from 5 to 180 mg/day (average 30–100 mg/day). Epidural lipomatosis is also seen in patients who use steroid inhalers or have had epidural steroid injections. It can occur as early as 6 months or more than 10 years after initiation of steroid treatment.

Idiopathic epidural lipomatosis rarely occurs in obese patients who may or may not have concurrent hypercortisolism. An abundance of epidural fat and congenitally narrowed spinal canal are predisposing factors.

Clinical Presentation

Weakness is the most frequent (72%) symptom and finding. Progressive paraparesis sometimes develops over months. Acute irreversible paraplegia rarely occurs. Other common complaints include low back pain (66%), radicular pain (50%), numbness/dysesthesias (50%), and changes in muscle stretch reflexes (50%). Lumbar radiculopathy, cauda equina syndrome, and neurogenic claudication are other possible manifestations.

Diagnosis and Treatment

Extraaxial tumors, epidural abscess, epidural hematoma, and other rare extrinsic compressive processes need consideration.

MRI is the study of choice, especially noting the unique signal characteristics of fat. When MRI cannot be performed, CT/myelogram demonstrates complete block in 69% of patients.

Weight loss and discontinuation or reduction of the corticosteroid dose are the primary medical modalities. The choice of medical versus surgical management is based on the severity of the clinical picture, possibility for reversing the causative mechanism, and the potential for surgical complications. Sometimes a multilevel laminectomy with debulking of lipid tissue is required; however, this has high morbidity and mortality.

Clinical Vignette

A 43-year-old woman had a history of numbness and cold sensation in her right leg for several months. She did not perceive pain in her right leg when she cut it while shaving. She felt that her tennis game was slipping. Medical history was otherwise unremarkable.

Initial neurologic exam was normal. At follow-up 6 weeks later, her exam demonstrated reduced light touch, pinprick and temperature sensation to a level of T12 on the right. Position and vibration senses were intact. Strength, gait, and reflexes were normal.

MRI demonstrated a thoracic meningioma on the left at T5–T6 that was intradural and extramedullary. The spinal cord was markedly thinned. Surgical resection of the meningioma led to rapid and full recovery.

Spinal cord meningiomas comprise at least 25% of primary spinal cord tumors although they are less common than intracranial meningiomas (Box 45-3). Most are intradural. They can be located ventrally, dorsally or laterally to the cord.

Pathophysiology and Etiology

Typically, corticospinal tract dysfunction is the most prominent feature of cord compression secondary to an intradural extramedullary tumor. As the tumor enlarges, spinothalamic tract and dorsal column compromise also become evident. Localized radicular pain sometimes occurs; this is secondary to mass effect on adjacent nerve roots by the meningioma.

Spinal cord meningiomas have the same histologic classification as intracranial meningiomas (Chapter 51) and can become densely calcific. Meningothelial (syncytial), psammomatous, transitional, and fibroblastic meningiomas are seen; meningotheliomatous meningiomas are the most frequent.

Clinical Presentation

Almost any age group may present with a meningioma; individuals in their fourth to seventh decades are most vulnerable, particularly women. The thoracic cord is the most frequent site (~80% of cases); however, on occasion these occur in the high cervical cord at the foramen magnum. Meningiomas rarely occur at the lumbar level. Localized radicular pain may antedate other symptoms, as the nerve root is affected early on. Weakness, sensory loss, bladder and bowel dysfunction, and gait difficulty very gradually occur.

Spasticity, hyperreflexia, and Babinski signs ipsilateral to the lesion characterize the corticospinal tract involvement. Ipsilateral loss of proprioception may occur from pressure on the dorsal columns. When the spinothalamic tract is affected, contralateral pain and temperature loss are produced. When this is combined with corticospinal tract involvement, it is referred to as the Brown–Sequard syndrome indicating a hemi-cord lesion.

Diagnosis

Intradural extramedullary spinal tumors include meningiomas, schwannomas, and neurofibromas. Ependymomas can affect the filum terminale or any part of the spinal cord. Other spinal cord tumor categories include extradural and intradural intramedullary lesions (Table 45-2). Additional diagnoses in the differential are MS, spinal dural AVMs, vitamin B₁₂ deficiency, central disc herniation, and syringomyelia.

Table 45-2 Chronic Intradural Intramedullary Myelopathies