Monday, May 17, 2021

Brain & Spine Disorders

Intradural Tumors of the Spine

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Intradural spinal cord tumors have a prevalence of 3-10/100000 per year. They predominantly occur in the middle-aged group. The most common tumors are nerve sheath tumors (schwannoma and neurofibroma) which account for about 30%, and meningiomas, which account for another 25%. The remainder include intramedullary tumors. The most common intramedullary tumors are astrocytomas and ependymomas. Hemangioblastomas, cavernomas, dermoids, epidermoids and lipomas and others are even more uncommon.

Since the majority of these tumors are benign and slow growing there is often an indolent clinical course. Pain along the spinal axis is the most common complaint often persisting for several years before it leads to evaluation and imaging workup. Sixty to 70 % of the adult patients have pain as their initial symptom.

The pain is described differently in extra- vs. intramedullary lesions. Extramedullary tumors are eccentric in location and thus produce mostly unilateral, segmentally distributed pain. Intramedullary tumors more frequently cause diffuse dysesthetic pain, that is most pronounced during the early morning hours.

Motor and sensory deficits produced by extramedullary tumors are often segmental or unilateral, not infrequently of a Brown-Sequard type, while in intramedullary tumors they are usually diffuse.

Tumors involving the conus or the cauda equina may selectively impair sphincter control and sexual function, and these symptoms may precede other neurologic signs for months or even years. This may be misdiagnosed for some sort of "functional" entity before imaging reveals the true nature of the lesion.

The extent of tumor growth and neurologic involvement depends upon the location of the tumor within the spinal canal. Lesions in the upper cervical spine tend to involve the upper extremities. Involvement of the thoracic region evokes sensory and motor changes in the abdomen or lower extremities.

Extramedullary Tumors
  • Nerve sheath tumors usually arise from the dorsal roots. These include Schwannomas and neurofibromas.  These tumors are relatively avascular, globoid and without calcification. The dorsal root is intimately involved in the tumor and can rarely be preserved during surgical resection. When these tumors have a dumbbell configuration the size of the extradural component may exceed the intradural component.
  • Meningiomas, unlike nerve sheath tumors, arise from arachnoid cluster cells and thus can be separated from the nerve roots. These tumors tend to have a lateral or ventrolateral relationship to the spinal cord. They may arise in any age group, mostly occurring between the 5th and 7th decade of life, and tend to have a female preponderance. The thoracic region accounts for 80% of these tumors.
Intramedullary Tumors
  • Astrocytomas are the most common intramedullary tumor. They occur at any age but are most frequent in the first three decades. The majority of these neoplasms are benign. They vary in appearance and are not well demarcated from the surrounding neural tissue. Cysts lined by non-neoplastic tissue frequently accompany these tumors.
  • Gangliogliomas are benign neoplasms, common in children and young adults. They consist of well-differentiated neoplastic neurons and astrocytes. The neurons are readily recognized by their characteristic nuclear and nucleolar features, abundance of cytoplasm, content of Nissl substance, and the presence of argyrophilic neuritic processes. Their expression of neuronal markers like synaptophysin and neurofilament proteins also serve to identify these abnormal neurons. Most gangliogliomas grow slowly and have an indolent course.
  • Ependymomas are the most common intramedullary neoplasm in adults, while in children they account for only 10% of all intramedullary tumors. These tumors typically have a central location in the spinal cord. They occur throughout the spinal axis. At surgery ependymomas appear reddish gray with variable blood supply which always comes from the anterior spinal artery. They are well delineated from the surrounding spinal cord and have rostral and caudal cysts which cap the tumor poles. They are histologically benign.
  • Hemangioblastomas account for 3 to 7% of all intramedullary spinal cord tumors and are particularly rare in children. They occur throughout the spinal canal. Spinal hemangioblastomas are mostly sporadic, but up to 25% of patients will have von Hippel-Lindau disease.
Magnetic resonance imaging (MRI) is the imaging study of choice to evaluate intradural neoplasms. MRI formidably shows anatomical details with minimal artifact from the surrounding osseous structures. It provides a triplanar view of the neoplasm which allows accurate differentiation between intramedullary and extramedullary tumors. Intravenous gadolinium contrast, and particularly with the recent advances in MR technology, such as faster pulse sequences, and cardiac gating, MRI has become increasingly accurate in predicting the histologic tumor type.

Surgery is the most effective treatment for all intradural neoplasms and requires special expertise from your surgeon. Long term control or cure can be achieved with total removal for the extramedullary tumors and the majority of intramedullary neoplasms. Thus, early diagnosis and aggressive initial surgery provide the best opportunity for long progression-free survival. Subsequent surgery is generally more difficult due to scarring.  The surgical exposure should encompass the tumor with some rostral and caudal margins to allow for adequate visualization. In children or young adults, osteoplastic laminoplasty may reduce the incidence of postoperative deformity.  Dr. Aryan specializes in complex surgery for tumors of the spinal column and spinal cord.

Surgery for Extramedullary Neoplasms
For resection of extramedullary tumors the bony removal must be wide on the ipsilateral side and may include the facets. After the bony exposure is achieved, the surgical principle is to remove the neoplasm with minimal traction on the spinal cord. The surgeon should also avoid injury to the nerve roots. In large tumors this may be accomplished by an intracapsular decompression before the tumor is removed. The ultrasonic surgical aspirator (CUSA) or the laser allow for rapid debulking without displacing the surrounding neural tissue.
  • In nerve sheath tumors which arise from the dorsal roots, the nerve root is intimately involved in the tumor. These tumors can rarely be separated from these roots. Therefore these dorsal roots may be sacrificed over a few segments in the thoracic region, however only very few dorsal rootlets should be sacrificed in the cervical region. These tumors rarely are adherent to the spinal cord and can easily be separated away from it.
  • Meningiomas which are located ventrally or ventrolaterally pose more of a surgical challenge. A wide laminectomy with debulking of the tumor permits the surgeon to maneuver it out from under the ventral area of the spinal cord. In most instances, the tumor attachment is at the dura while adhesions to the spinal cord are relatively minor.
Surgery for Intramedullary Neoplasms
The exposure is similar to extramedullary tumors. The dura is then opened and secured with several tack-up sutures. It is important to emphasize that the swollen spinal cord is often rotated and distorted. It is essential to identify normal landmarks prior to performing a myelotomy. The myelotomy is performed over the center of the tumor using either bipolar cautery and an arachnoid knife or a laser (carbon dioxide or Nd:YAG).
  • Astrocytomas are gray in color, and they do not have a plane of dissection from normal spinal cord tissue. These neoplasms should be removed from "inside out" until a glial tumor interface is recognized by the change in color and consistency of the adjacent tissues. The excision of the astrocytoma is initiated in the mid-portion rather than the rostral or caudal pole of the neoplasm because the poles of the neoplasm have the least volume of tumor tissue, and removal of this part of the neoplasm may therefore be the most hazardous. The last fragments of the rostral and caudal segments of the tumor are removed by working within the myelotomy and distracting the residual neoplasm into the surgical cavity without extending the myelotomy.
  • Ependymomas are red or very dark gray and have a distinct cleavage plane between tumor and the adjacent neural tissue. Small tumors may be removed in one piece, whereas bulky ones must be excised in a piecemeal fashion. In these cases, it is hazardous to attempt an en bloc excision, as there will be excessive manipulation of adjacent neural tissue. In these cases, the center of the tumor must first be debulked, and only then should the cleavage plane between tumor and adjacent tissue be developed. This is accomplished by retracting the tumor tissue into the residual cavity, and not retracting the spinal cord from the tumor. There is usually an area of tumor tissue which is adherent to the anterior median raphe. These fragments must be removed in bits and pieces, and with sharp dissection to avoid injury to the anterior spinal artery.
  • Hemangioblastomas are most commonly located on the dorsal or dorsolateral surface of the cord. These lesions are, of course, vascular and therefore the surgeon should not enter the tumor because bleeding may be difficult to control. The dissection should proceed around the tumor surface with cauterization of the feeding vessels and tumor capsule. It is advisable to preserve at least one venous pedicle until all feeding arteries are divided.
Intraoperative Neurophysiological Monitoring
Intraoperative monitoring with motor evoked potentials (MEPs) is a direct motor tract monitoring technique which is becoming the major monitoring tool for spinal cord surgery. The D-waves and muscle MEPs must be interpreted together. Loss of muscle MEPs during a spinal cord tumor resection indicates at least a temporary disruption of motor function of the spinal cord. The more incremental change of the D-wave amplitude then allows further interpretation of the motor outcome. A loss of muscle MEPs is highly associated with a temporary motor deficit in the lower extremities, even if the D-wave amplitude is unchanged. In the majority of cases, this is even side specific. As long as the D-wave amplitude remains above a cutoff value of about 50% of its baseline value, this motor deficit is temporary, with the patient recovering to preoperative strength within hours to days, sometimes weeks. A further decline in D-wave amplitude or its loss is associated with a long-term severe motor deficit.

Somatosensory evoked potential (SEPs) recording is of use to assess the functional integrity of the sensory system. Their correlation with postoperative motor function is poor and particularly in intramedullary surgery SEPs usually disappear when the midline myelotomy is performed and are then of no further use for the critical assessment of the motor system.

Radiotherapy & Radiosurgery 
While surgery is the treatment of choice for both intra- and extramedullary tumors, some authors have recommended biopsy and radiation to manage astrocytomas and ependymomas. The beneficial results of these studies may be related to the effects of the decompressive laminectomy rather than the adjuvant treatment. The recommended radiation dose is hazardous to the spinal cord, especially in children and young adults, where myelopathy has been reported to occur with doses of 30 Gy. There is no role of radiotherapy in treatment of intradural extramedullary tumors other than metastatic disease.  If radiation therapy is indicated, stereotactic radiosurgery may be the most optimal form of radiation therapy.  This should be performed with the involvement of a neurosurgeon, and Dr. Aryan is an expert on radiosurgery for tumors of the spine.  

Tumors of the Spine

Spine Disorders

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