FORENSIC NEUROPATHOLOGY



FORENSIC NEUROPATHOLOGY

WILLIAM A. COX, M.D.

FORENSIC PATHOLOGIST/NEUROPATHOLOGIST

SPINAL EPIDURAL HEMATOMA

September 28, 2009

GENERAL INFORMATION

Intraspinal hemorrhage can occur in one of three extramedullary compartments: subarachnoid, subdural and epidural. Sometimes you will see these hemorrhages referred to as extra-axial bleeds, which means the hemorrhage is occurring outside of the brain or spinal cord tissue. Intra-axial bleeds are those hemorrhages, which occur within the substance of the brain or spinal cord. Such hemorrhages are also referred to as intraparenchymal or if they occur in the ventricles of the brain, intraventricular. Another infrequently used term to describe extramedullary hemorrhages involving the spinal cord is hematorrhachis. Hematomyelia is a term used to describe hemorrhages in the substance of the spinal cord (intra-axial). These latter two terms are primarily seen in the neuropathology literature.

Spinal epidural hemorrhages (SEH) are rare. They occur most commonly in childhood and the fifth and sixth decades of life, with the exception of spontaneous spinal epidural hemorrhages (SSEH), which are extremely rare in childhood. SEHs have a higher frequency in males than females. In childhood they occur most commonly in the cervical region, whereas in the adult they occur most commonly in the posterior aspect of the thoracic and lumbar regions.

The major concern that these hemorrhages present is acute compression of the cord by encroachment on its space. This is especially true when you take into consideration the extremely confined space that the spinal canal presents.

In order that we better appreciate the clinical presentation of SEHs it is important that we have a general understanding of the anatomy of the spinal cord.

ANATOMY

The spinal cord is a long, cylindrical structure, which extends from the base of the skull, the cranial border of the atlas (first cervical vertebrae), to the lower border of the first lumbar vertebrae. It measures approximately 45 cm. (17.7 inches) in length in males and 43 cm. (16.9 inches) in females. This is in contrast to the length of the vertebral column, which is approximately 70 cm. (27.6 inches). What you need to remember is the precise level the cord terminates does show variability, showing some correlation with the length of the trunk, which is especially true in females. The cords termination may be as high as the lower third of the twelfth thoracic vertebra to as low as the second and third lumbar vertebrae. The spinal cord is enclosed by three membranes, which are from the outside in, the dura mater, arachnoid and pia mater. There are three areas in which blood can accumulate: the epidural space, which is external to the dura mater, the subdural space, which is a potential space due to the fact the arachnoid membrane is adherent to the dura mater and internal to the dura, and the subarachnoid space, which normally contains cerebrospinal fluid.

At the base of the skull the spinal cord is continuous with the medulla oblongata of the brain stem. At its most inferior point it terminates in a structure called the conus medullaris. At the level of the conus medullaris, the pia mater, which is the cellophane-like membrane that is adherent to the outer surface of the nervous tissue forming the spinal cord, condenses to form the filum terminale. This is a connective tissue filament that continues inferiorly in the spinal canal, eventually penetrating the dura at the level of the second sacral vertebra, thus forming the coccygeal ligament, which descends to the first coccygeal segment.

Although, the spinal cord is described as being cylindrical, in reality it is not, being greater in its transverse dimension at all levels, which is especially true in its cervical segments and to a lesser extent in its lumbar segments.

When you look at the spinal cord it appears to be a continuous cord-like structure, however anatomically, as well as functionally, it consist of 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal segment. Each segment receives and gives rise to pared dorsal nerve roots (rami), which anatomically come off the back of the spinal cord with each member of the pair opposing each other on opposite sides and ventral nerve roots (rami), which anatomically come off the front of the spinal cord with the same arrangement as the dorsal roots, one on each side. There are two exceptions to each spinal cord segment receiving paired dorsal nerve roots: dorsal nerve roots are usually absent in the first cervical and the coccygeal roots. This is due to the fact there are no corresponding dermatomes for these segments. The dorsal and ventral nerve roots fuse within the spinal canal to form spinal nerves, with the actual fusion taking place within the corresponding intervertebral foramina beneath the vertebrae of the same number with two exceptions: the first cervical nerve emerges between the atlas and the base of the skull (occiput) and the eighth cervical nerve emerges from the intervertebral foramen between C7 and T1. The intervertebral foramina are apertures, of which there are two in number between every pair of vertebrae. They allow for the passage of the spinal nerves, dorsal root ganglion, the segmental arteries derived from the spinal branches of the vertebral, deep cervical, intercostals and lumbar arteries, communicating veins between the internal and external plexuses, recurrent meningeal nerves, and the transforaminal ligaments.

The dorsal nerve roots are composed of sensory fibers, the cell bodies of which lie in the spinal ganglion that is outside the spinal cord, but within the spinal canal. The spinal ganglions are ovoid swellings on the dorsal roots, which contain cell bodies of afferent neurons that carry impulses from the periphery to the spinal cord. The dorsal roots innervate the intrinsic dorsal muscles of the back and neck, and the overlying skin from the vertex to the coccyx. These muscles constitute the extensors of the vertebral column. In the middle of the back the cutaneous area innervated roughly corresponds to that of the underlying muscles, but in the upper and lower portions of the trunk it widens laterally to reach the acromial region above and the region of the greater trochanter below. With certain exceptions the dorsal nerve roots have a typical segmental distribution, the field of each overlapping with that of the adjacent segments above and below. Deviation of this segmental distribution is found in the upper two cervical nerves and in the lumbosacral rami.

The ventral nerve roots consist of efferent (fibers running from the neurons within the spinal cord to the periphery, which includes the skeletal muscles, skin and sense organs, otherwise referred to as the somatic system) and, at certain levels, visceral (sympathetic) nerve fibers, the axons of which are arising from their sources in the spinal cord. The ventral nerve roots supply the ventrolateral (anterior and lateral) muscles and the skin of the trunk, as well as the extremities. In the thoracic region they run independent of one another, but in the cervical, lumbar, and sacral regions they unite near their origins to form plexuses, which are referred to as the cervical, brachial and lumbosacral plexuses. The plexuses will be discussed in a subsequent article.

In essence the spinal cord receives afferent inputs via the dorsal roots from somatic and visceral receptors in most parts of the body, gives rise to pulses to higher levels of the neuraxis, gives rise to fibers emerging in the ventral roots that innervate somatic and visceral effectors, conveys descending pathways from higher levels of the nervous system and participates in a variety of somatic and autonomic reflexes.

CAUSATION

The underlying cause of these SEHs is most often due to trauma. However, they can occur spontaneously with no apparent underlying cause, as the result of lumbar puncture of spinal surgery, epidural anesthesia, vascular malformations, tumors, bleeding diatheses either disease-related coagulopathy or therapeutic bleeding due to anticoagulation, liver disease with portal hypertension, arthropathies such as Paget’s disease and ankylosing spondylitis, herniation of an intravertebral disk, hypertension, chiropractic manipulation, valsalva maneuver, and during pregnancy and delivery. Approximately 40% of SEHs have no known underlying etiology.

Most believe the actual source of the SEH is the epidural venous plexus, although in rare cases the source can be arterial. This typically gives rise to rapidly developing clinical symptoms secondary to pressure on the spinal cord and dorsal or ventral rami.

CLINICAL PRESENTATION

Typically these patients present with severe sudden onset of neck or back pain with the eventual development of radicular pain; which can evolve into weakness (paraparesis-quadriparesis) or paralysis (paraplegia-quadriplegia). The level of the hemorrhage in the spinal canal determines whether the patient manifest paraparesis-quadriparesis or paraplegia-quadriplegia.

The terms paraparesis and quadriparesis imply weakness of the lower extremities and all four extremities respectfully. They are indicators of incomplete paralysis. Paraplegia and quadriplegia refer to paralysis of the lower extremities and variable portions of the trunk and all four extremities respectfully. Paraplegia is due to compression of the spinal cord below the nerve roots forming the brachial plexus (C5-T1), with a small contribution from C4. Quadriplegia indicates cord compression and or transaction above the level of C4.

Radicular pain refers to pain that travels along a particular nerve, hence it radiates, due to pressure on a nerve root as it arises from the spinal canal. An example is sciatica. The sciatic nerve runs down the buttocks through the back of the thigh, traveling behind the knee, sending branches to the hamstring and continues downward to the foot. The radicular pain involving the sciatic nerve is due to compression of the nerve roots forming the nerve, which arise from L5 to S3.

The patients may also complain of numbness, difficulty in breathing, urinary incontinence and fecal incontinence.

Patients with numbness often describe a sensation of “pins and needles”. Another term that is used for numbness is paresthesias. One of the things you want to keep in mind is that if the patient says the numbness (paresthesias) come and go, than this is an indication they are not likely due to a neurologic condition. If however, the numbness does not go away this is a reliable indication of an underlying neurologic disorder.

Some patients may complain of difficulty in breathing, which is not uncommonly associated with either quadriparesis or quadriplegia. This indicates cord compression above the level of C4, with its consequent interference of the contribution of C3 and C4 to the phrenic nerve (C3-C5). This nerve contains mostly motor fibers that innervate the diaphragm. The actual degree of dysfunction of the diaphragm is dependent on the actual nerve contribution to the phrenic nerve, which will be discussed in a subsequent article.

Urinary incontinence is not uncommon after trauma to the lower spinal cord, either due to cord compression by a SEH or contusion, laceration or crushing of the cord. This results in nerve impulses between the bladder musculature (detrusor muscle) and it’s external sphincter muscle and the urethral external sphincter muscle and that portion of the cord being disrupted. In order to initiate normal urination, nerve impulses must travel via the visceral motor fibers of S2 through S4 to the bladder musculature via the short postganglionic parasympathetic fibers to induce contraction of the detrusor muscle. Simultaneously nerve impulses must travel via the somatic nerves of S2 through S4 to relax the external sphincter muscles. For normal urination to take place these two events must occur simultaneously.

The actual urge to urinate is determined by pressure within the bladder. This is called intravesicle pressure. In adults, when the bladder accumulates between 140 to 180 ml of urine it produces an intravesicle pressure of 15 to 16 cm of water, which creates the desire to urinate. This desire requires proper function of afferent nerves in the hypogastric nerves and plexus traveling from the bladder to the spinal cord segments T12 to L2. It is this segment of the spinal cord that contains the “vesicle center for the retention of urine.” Also, while the bladder is filling somatic motor neurons in the ventral horn of the sacral spinal cord send impulses to the striated muscle fibers in the external urethral sphincter, causing it and the striated muscle fibers in the external sphincter muscles of the bladder to contract. These motor neurons are stimulated by visceral afferents that are activated when the bladder is only partially full. As the bladder fills, spinal sensory afferents relay this information to a region in the pons that coordinates micturition. This pontine area, sometimes called Barrington’s nucleus also receives important descending inputs from the frontal lobes concerning behavioral cues for emptying the bladder. Descending pathways from Barrington’s nucleus cause coordinated inhibition of sympathetic and somatic systems, relaxing both sphincters. The onset of urinary flow through the urethra causes reflex contraction of the bladder that is under parasympathetic control. Consequently, trauma to this section of the spinal cord can give rise to some degree of urinary dysfunction, either partial or complete, the exact level of which is determined by the degree of the compression induced by the SEH and how soon it is evacuated.

In patients with spinal cord injuries at the cervical or thoracic levels, the spinal reflex control of micturition remains intact, but the connections with the pons are compromised. Consequently, micturition cannot be voluntarily controlled. When it does occur as a spinal reflex resulting from bladder overfilling, urination is incomplete.

You need to keep in mind that patients with traumatic spinal cord injuries often have head injuries. This is important when evaluating urinary and fecal incontinence. Portions of the superior frontal gyrus on the medial surface of the cerebral hemisphere are involved in the control of micturition and defecation. Lesion in this region, involving one or both frontal lobes, may cause urgency, frequency of micturition or incontinence. Such lesions are also associated with lack of awareness of all vesicle events, including the sensation of the desire to micturate and the sensation that micturition is imminent.

Although, it is generally thought that the pathophysiology of urinary and fecal incontinence is similar, in reality there are major differences between the two. The underlying reasons for these differences are due to two factors: the bladder wall, unlike the wall of the gastrointestinal tract, does not contain a complex neuronal network (myenteric plexus of Auerback and the submucosal plexus of Meissner); the content of the bladder is liquid whereas that of the bowel varies between liquid and solid. Consequently, the pathophysiology of the bladder response to spinal cord injury is different from that of the gastrointestinal tract. As indicated above the contraction or relaxation of the detrusor muscle, the urinary bladder external sphincter muscle and the urethral external sphincter muscle is in response to external stimuli, which are modulated by the central nervous system. The peristaltic activity of the gastrointestinal track, although affected by external stimuli, is not dependent on such stimuli, since coordinated peristalsis occurs on stimulation (colonic response to food) of the gut after section of all nerves, which connect the aforementioned plexuses with the central nervous system. Of the two plexuses, it is the myenteric plexus, which serves as the major nerve supply to the gastrointestinal tract and thus controls gastrointestinal motility. Meissner’s plexus innervates cells in the epithelial layer and the smooth muscle of the muscularis externa. To further demonstrate the point that the pathophysiologic mechanisms underlying voiding and defecation dysfunction are not the same is that patients with spinal cord injuries that have given rise to total sensory and motor deficit in the anorectal region, do not typically show incontinence after a short period of time following the injury. This is primarily due to fact that there is an increase in the consistency of the feces, which in of itself prevents leakage. Such a phenomenon does not occur in the bladder, which is due to two factors: the consistency of the liquid does not change and if there is no bladder external sphincter and urethral external sphincter tone, urinary incontinence takes place.

It should not be misconstrued that colonic motility is unaffected by spinal cord injury. It has been clearly demonstrated that the normal colonic motility is decreased, as is motility following food stimulation. However, the degree of hypomotility is not uniform throughout all segments of the colon and is not related to the level or completeness of the injury. Although there is a decrease in motility even following food stimulation when compared to the normal baseline, there is an increase in colonic motility following the ingestion of food, although it is not as great as in the normal colon.

What must be understood is that the level of the spinal cord injury, whether due to compression by a SEH, contusion or crushing of the cord, does not give an indication of bowel function. This is clearly demonstrated by the fact that some studies have demonstrated the same motor behavior of the large bowel in quadriplegic and paraplegic patients.

Spinal shock is typically not a feature of SEH, but rather a reflection of an acute traumatic injury to the cord, which can be incomplete or complete. However, autonomic dysreflexia (dysautonomia) may be seen, although again is more often associated with partial or complete crushing or transection of the cord. In general autonomic dysreflexia is seen in cord injuries from T6 or higher, with approximately 85% having traumatic cord lesions above C6. It is primarily due to a loss of inhibition of higher sympathetic outflow and abnormal reorganization of interneurons, which can lead to sudden life threatening changes in blood pressure, heart rate, and temperature. This may manifest itself by the patient suddenly developing an acute cardiac arrhythmia either at the scene or on the way to the hospital. Although not of concern to the EMTs or Paramedics responding to the scene, autonomic dysreflexia can develop at anytime immediately after the accident to years later, often being triggered by pain, fecal impaction, and abdominal distension and voiding.

SEH has also been associated with a number of syndromes, which include the Brown-Sequard syndrome, conus medullaris syndrome and cauda equina syndrome. Generally the Brown-Sequard syndrome is described as the result of hemisection of the spinal cord. Clinically it presents with weakness and spasticity in certain muscle groups due to pressure on the corticospinal tract associated with loss of discriminative touch, vibration and position sense (due to pressure on the dorsal columns) all of which are on the same side (ipsilateral) of the SEH. Mere contact and pressure appear normal; but tactile localization is poor and two-point discrimination and vibratory sense are lost or diminished. There is loss of pain and sensation on the opposite side of the body (contralateral) as the SEH. The reason the pain and temperature is lost on the opposite side to the epidural hemorrhage is that the neurons within the spinal cord, which are responsible for perception of pain and temperature, send their axons across the midline of the spinal cord and ascend to the thalamus in the antero-lateral column. In actuality this syndrome is fairly common in trauma to the spinal cord including SEHs.

The conus medullaris syndrome as seen in spinal epidural hematomas is due to compression of the sacral cord segments S2 to S5. This manifest itself as anesthesia in the distribution of S3-S5 (perianal or saddle anesthesia), paralysis of the external sphincter of the bladder and urethra giving rise to bladder distention followed by involuntary overflow incontinence and bowel dysfunction due to loss of anal tone, and impotence. The bulbocavernosus (S2-S4) and anal (S4-S5) reflexes are absent. Muscle strength is for the most part preserved. There is also normal sensory and motor function in the lower extremities. Involvement of the conus needs to be distinguished from those of the cauda equina syndrome, which involve the cluster of nerve roots derived from the lumbosacral roots.

The bulbocavernosus reflex is a clinical test utilized to determine the extent of spinal cord injuries and whether spinal shock exists. The test involves checking for anal sphincter contraction as the glans penis is squeezed. If the patient has an indwelling Foley you can do the same test by pulling on the Foly. The reflex involves the function of S2-S4. In the absence of spinal cord trauma, a negative reflex indicates the patient has spinal shock. If there is evidence of trauma and this reflex is absent, than the patient has suffered an injury to the conus medullaris or sacral nerve roots S2 –S4.

The anal reflex (perineal reflex) is the contraction of the external anal sphincter on stroking the skin around the anus. This reflex is the result of nerve impulses traveling from nociceptors in the perineal skin through the pudendal nerve to the spinal cord segments S4-S5. Absence of this reflex indicates there is an interruption of the reflex arc either involving the sensory afferent limb, the lower sacral segments or the motor efferent limb. A nocicepter is a sensory receptor that sends nerve impulses to the spinal cord and brain in response to potentially injurious stimuli. Nociception usually causes the perception of pain.

The cauda equine syndrome is the result of pressure or traumatic induced lesions to the lumbosacral roots surrounding the filum terminale. It manifests itself by low back or radicular pain, asymmetric leg weakness and sensory loss, variable absence of neurologic reflexes (areflexia) in the lower extremities and relative sparing of bowel and bladder function. If the epidural is large enough you can see a mixed picture constituted by the combination of the conus medullaris and cauda equine syndromes.

FUNCTIONAL CONSIDERATIONS

Nerve compression due to trauma can result in a variety of dorsal and or ventral root symptoms, usually associated with pain of short duration. Although pain is the primary symptom, the patients typically also complain of numbness (paresthesias), which are restricted to the dermatome supplied by the affected dorsal roots. If the ventral roots are involved than the pain is associated with muscle spasms, weakness and vasomotor disturbances; hence, an understanding of the segmental distribution of the spinal nerves is helpful in evaluating root lesions. The segmental distribution of the spinal nerves will be discussed in a subsequent article. It must be remembered that a transection of a dorsal root seldom produces a complete loss of sensation (anesthesia), however it can give rise to a depression in reflexes (hyporeflexia) in areas supplied by that root. The reason that you do not see a complete loss of sensation is due to the overlapping distribution of fibers of adjacent roots; consequently, complete loss of sensation tells you several contiguous roots have been subjected to trauma. The associated hyporeflexa involves superficial and deep reflexes and is also associated with a decrease in tone (hypotonia) in the affected muscles.

Just as trauma to a dorsal root seldom produces complete anesthesia, trauma to one spinal segment or ventral root will cause weakness, but not complete paralysis, in all muscles innervated by this segment. This is due to the fact that the motor neurons, which innervate a single muscle, extend longitudinally through several spinal segments and that there are several such cell columns at each spinal level. Complete paralysis will occur only when the lesion involves the column of cells in several spinal segments that innervate a particular muscle, or the ventral roots that arise from these cells. Since most of the muscles of the upper and lower extremities are innervated by nerves of motor neurons extending through three spinal segments, complete paralysis of a muscle suggest a central lesion involving motor neurons in several spinal segments or trauma involving ventral roots of several consecutive spinal segments. It is also important to remember that since there are several adjacent cell columns, which are responsible for innervating adjacent muscles will also be injured, trauma to segments of the spinal cord will involve muscle groups rather than individual muscles.

RADIOLOGIC STUDIES

The optimum radiologic investigation for spinal epidural and subdural hematomas is to utilize MRI and plain CT as complementary studies. If MRI is not available you can use CT myelography.

TREATMENT

Typically SEHs give rise to rapidly evolving clinical manifestations of spinal cord and or nerve root compression requiring immediate neurosurgical evacuation of the hematoma. Consequently, it is absolutely essential that the potential of a rapidly developing SEH be entertained, with the patient being transported as soon as possible to a facility, which has neurosurgical capabilities. It is only through immediate neurosurgical care that both the acute sequelae and long term consequences of SEHs can be mitigated

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