Surgical Management of Intramedullary Spinal Cord Tumors in Adults

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Chapter 186 Surgical Management of Intramedullary Spinal Cord Tumors in Adults

The neurosurgical literature on intramedullary spinal cord tumors (IMSCTs) contains many case reports and few large series, even for tumors of glial origin, which are the most numerous.¹^–¹⁵ As a matter of fact, these lesions are relatively rare and occur in any age group. Indeed, IMSCTs account for 2% to 4% of all central nervous system tumors in adults and 15% of all primary intradural tumors in adults.¹⁶^–¹⁸ Ependymomas are the most common tumors in adults and astrocytomas are the most common in children.^11,¹⁹ Hemangioblastomas and cavernomas represent special entities and require specific strategies.^20,²¹ Other tumors of nonglial origin are still more exceptional. It is well known that IMSCTs have no typical clinical presentation.

At present, magnetic resonance imaging (MRI) is the best and, in most cases, the only examination to perform in investigating these cases. Although MRI can be a highly accurate diagnostic tool, it does not always provide accurate differentiation between ependymomas and astrocytomas. Evoked potentials, both sensory and motor, are now standard intraoperative monitoring tools used during the surgery of these lesions.²²^–²⁴ The ultrasonic aspirator is now used routinely and provides significant assistance.

Whenever possible, we aim at achieving complete removal of spinal cord benign tumors irrespective of the histologic types; however, the surgical treatment of intramedullary spinal cord tumors is not routine surgery. The operative duration is often very long and the procedure is always delicate and technically difficult. That is why neurosurgeons specializing in this field of neurosurgery are not numerous.

Anatomy

The spinal cord is located entirely within the spinal canal. Its rostral end is in continuity with the caudal portion of the medulla, in front of the middle of the atlas anterior arch, to the upper border of the C1 nerve root. The spinal cord has the shape of a roughly cylindrical stem, is ventrally and dorsally slightly flattened, and whitish. It is 42 to 45 cm long and 1 cm wide in adults. It has an average weight of 30 g. It presents two enlargements. The cervical enlargement is 10 cm long, extending from the C4 to the T1 vertebral levels. The lumbar enlargement is 8 cm long from T9 to T12 and in continuity with the conus medullaris, which tapers off at the level of the L1–2 disc space into the filum terminale, an atrophic remnant of the caudal segment of the embryonic spinal cord.

The ventral surface is marked by a ventral fissure that runs along the entire length of the spinal cord. This 2- to 3-mm deep fissure splits the ventral aspect of the spinal cord into two symmetrical ventral columns 2 to 3 mm wide, the lateral borders of which give rise to the ventral roots. The anterior spinal artery runs along the ventral aspect of the cord but not in the anterior median fissure. The lateral surface of the cord contains a lateral column located between the entrance of the dorsal roots and the exit of the ventral roots. On the dorsal surface there is also a dorsal medial sulcus. Although it is not a fissure, it is also possible to separate its edges to visualize the sulcocommissural arteries, which are clearly identified under the microscope.

The spinal cord consists of gray matter surrounded with white matter. The gray matter has a typical H shape in cross section and is characterized by a vestigial central or ependymal canal, which runs the entire length of the spinal cord and is a remnant of a larger embryonic central canal, which is nearly always completely obliterated in adults by ependymal cells or neuroglial clusters. Sometimes this vestigial canal persists over a few millimeters in length, but it lies in the central substantia gelatinosa and is lined with ependymal cells. Such an ependymal canal becomes visible on MRI in the shape of a “split central cavity” without pathologic meaning. Otherwise, the vestigial canal may be dilated in hydrosyringomyelic cavities or in the satellite cysts of intramedullary tumors.

The spinal meninges differ from those of the brain owing to the presence of a thicker pia mater attached to the inner dural surface by the dentate ligaments. The medial border of each is adherent to the lateral column, all along the spinal cord. The lateral border of each ligament is free, with the exception of the areas adjacent to the roots. These are thick serrations whose apices are attached to the dura between the overlying and underlying root sheaths. The arachnoid consists of a dense impermeable superficial layer adjoining the dura and of fenestrated dorsal septa that run from the superficial layer of the arachnoid to the pial surface of the spinal cord. That is why the cord is strengthened by the meninges without interference with the free circulation of the cerebrospinal fluid in the subarachoid space. The spinal dura encloses the spinal cord and the cauda equina from the foramen magnum to the sacrum. The diameter of the dural tube is smaller than that of the spinal canal but is much larger than that of the spinal cord. The dura, which forms a cylindrical sheath, is separated from the spinal canal by the epidural space, containing fat and the epidural venous plexuses. That is why the spinal cord is protected by the meninges and the cerebrospinal fluid and can be slightly mobilized within the spinal canal.

The spinal cord is vascularized by the anterior spinal artery, which arises from the vertebral arteries, in the upper cervical region and by the pial anastomotic network supplied by the radiculospinal and radiculopial arteries, which run with spinal nerves. Because of their size, two ventral radiculospinal arteries have been distinguished: the artery of the lumbar enlargement (Adamkiewicz’s artery), which runs with a spinal nerve on the left side in 75% to 85% of cases and between T9 and T12 in 75% of cases, and the artery of the cervical enlargement, which follows the course of a nerve root between C4 and C8. The anterior spinal artery has a mean diameter of 200 to 500 μm. The posterior blood supply is provided by discontinuous arteries of smaller size (100 to 200 μm). The pial network and the radially penetrating arteries supply the white matter, and the central or sulcocommissural arteries arising from the anterior spinal artery supply the gray matter. Finally, the territory of the anterior spinal artery includes the anterior two thirds of the cord, and the remaining posterior third is supplied by dorsal vessels. The lack of anastomosis between central arteries and the pial network partially justifies the reputation of the midthoracic spinal cord as being “surgically fragile.”

Venous drainage takes place first via the intrinsic vessels, which drain in turn into the pial veins. The anterior spinal vein lies dorsal to the artery. The posterior dorsal vein, which is often very large (400 to 1000 μm), has a winding pattern, particularly in the thoracic region, and zigzags from one posterior column to the other over the posterior median sulcus.

The surgical approach of the intramedullary tumors depends on the anatomy of the cord and its vessels. The anterior approach to the ventral fissure is blocked by the anterior spinal artery and the branches arising from it. The posterior approach is not blocked by arteries or veins, but there is no open fissure on this side of the spinal cord. It is also possible to open the dorsal medial sulcus by separating its edges without damaging the dorsal columns and their vessels.

Incidence, Types, and Prognosis

IMSCTs can be classified in three main groups: tumors of glial origin, tumors of nonglial origin, and pseudotumors.

Tumors of Glial Origin

The group of tumors of glial origin is by far mainly represented by ependymomas and astrocytomas.^20,²⁵ Others, such as oligodendriogliomas, as rare.²⁶

Ependymomas

Spinal cord ependymomas (Fig. 186-1) constitute the most common IMSCTs in adult patients. They can reach a considerable size because they are slow-growing processes. The majority of spinal cord ependymomas have a good prognosis because most of the time they can be removed completely and are grade II according to the World Health Organization (WHO) classification. In the literature, the rate of complete removal varies from 69% to 97%.^3,^15,²⁷ The functional prognosis is particularly satisfying as far as patients who are operated on when their preoperative condition are still good. Indeed, according to the literature, 48% to 75% are stabilized after the procedure, 10% and 40% improve, and between 9% and 15% deteriorate.^3,^11,^15,^28,²⁹ This highlights the need for prompt surgery in case of neurologic deterioration.^3,^11,^15,^28,²⁹ The 5- and 10-year survival rates reach respectively between 83% to 96% and 80% to 91%.^11,^15,^27,²⁹^–³¹ Incomplete resection is considered the most important factor predicting recurrence.^3,^32,³³

FIGURE 186-1 Grade II cervical ependymoma. A to E, Preoperative magnetic resonance images (MRIs). A, Sagittal T2-weighted image. B, Sagittal T1-weighted image. C, Sagittal contrast-enhanced T1-weighted image. D, Axial contrast-enhanced T1-weighted image. E, Axial T2-weighted image. F to M, Perioperative views. F, Division of the pia mater above the medial sulcus. G, Midline approach with posterior columns separated like a book.Figure 186-1, cont’dH to J, The tumor is progressively resected by dissection of the tumor–spinal cord interface and debulking with an ultrasonic aspirator. K, Great care must be taken when reaching its anterior aspect to prevent any damage to the anterior spinal artery, which is often close to the lesion. L, View after complete resection of the lesion. M, The spinal cord has been closed. N to W, Early (N to R) and 9-month (S to W) postoperative MRIs comparable to A to E. Used with permission from Hôpital Erasme, Université Libre de Bruxelles.

Astrocytomas

Spinal cord astrocytomas (Fig. 186-2) represent more than 80% of the IMSCTs in children,¹¹ and in adults astrocytomas is the second most common type of tumor.¹¹ The fraction of pilocytic astrocytomas varies greatly in large studies, from more than 30% to more than 60%.^11,¹⁵ The percentage of anaplastic lesions or glioblastomas is higher in adults (25% to 30%) than in children (10% to 17%).^1,^5,^8,^11,³⁴^–³⁶ Unfortunately, unlike with ependymomas, radical resection is most of the time not possible at surgery because by nature grades II to IV tumors display an infiltrative behaviour. Surgery consists then in removing as much tumor as possible or, in some circumstances, in performing only biopsy or decompression with duraplasty. The reported rates of complete and subtotal removal vary respectively between 11% to 31% and 21% to 62%.^11,^15,³⁷ Pilocytic astrocytomas and the surgeon’s experience are factors associated with higher rates of complete resection.^11,¹⁵ In low-grade astrocytomas the 5- and 10-year survival rates rise about 77% to 82%, but this rate drops to 27% and 14% for malignant ones.^11,³⁸ Low spinal level (conus), malignant grade, and adult age are considered important factors in relation with higher tumor recurrence rate.¹¹ The amount of resection has not been found in relation with the progression-free survival or the overall survival in many series when tumor debulking has been carried out,^6,^11,^16,^35,^38,³⁹ whereas it was for others in low-grade astrocytomas.⁵

FIGURE 186-2 Grade III cervical astrocytoma. A to D, Preoperative magnetic resonance images (MRIs). A, Sagittal T2-weighted image. B, Sagittal T1-weighted image. C, Sagittal contrast-enhanced T1-weighted image. D, Axial contrast-enhanced T1-weighted image. Arrows on Figures C and D show areas of enhancement. E to G, Postoperative MRI after biopsy and duraplasty.

Used with permission from Hôpital Erasme, Université Libre de Bruxelles.

Gangliogliomas

Gangliogliomas are very uncommon lesions mainly reported as case reports and a few series.^10,⁴⁰ These tumors develop mainly in children and young adults.¹⁰ In a large series of 56 patients, complete or subtotal resection has been obtained in 82% and 18% of the cases with 5-year actuarial survival rate of 88% and progression-free survival rate of 67%.¹⁰

Outcome Factors

The major determinant of long-term patient survival is the histologic composition of the tumor. Indeed, the 5-year progression-free survival rate drops from 78% for low-grade gliomas down to 30% in high-grade gliomas.⁵

A longitudinal database (Surveillance, Epidemiology, and End Results [SEER] database) encompassing 26% of the U.S. population has been published including 1814 patients suffering from a spinal cord glioma.¹³ In this study, age, histology, and grade were defined as significant predictors of outcome.¹³

Tumors of Nonglial Origin

Within the group of tumors of nonglial origin, hemangioblastomas and cavernomas are the most common. These are benign vascular tumors, being characteristically well delineated and sometimes multifocal. Other lesions such as metastasis, epidermoids, dermoid cysts, lipomas, intramedullary schwannomas, primitive neuroectodermal tumors (PNET), and teratomas can also be enumerated.^11,^25,³⁹ Besides these rare tumors, we have also encountered lymphomas and neuroglial cysts.

Hemangioblastomas

Hemangioblastomas (Figs. 186-3 and 186-4) represent almost 2% to 15% of IMSCTs in some series.^11,^15,^21,^24,^41,⁴² These highly vascular lesions consist of two main components: large vacuolated stromal cells, which have been identified as the neoplastic cell of origin, and a rich capillary network.⁴³ Hemangioblastomas are often observed as an encapsulated lesion abutting the pia, especially at the posterior or posterolateral aspect of the spinal cord nearby the dorsal root entry zone, but they may be also observed anteriorly or, rarely, are purely intramedullary.^11,^21,⁴² Radicular arteries or anterior branches provide the blood supply to these lesions.⁴⁴ Associated cyst and syrinx, present in 80% to 90% of cases, and edema can be responsible for significant neurologic morbidity.²¹

FIGURE 186-3 Left anterior cervical hemangioblastoma. A and B, Preoperative contrast-enhanced magnetic resonance image (MRI) in axial and sagittal planes. C, Postoperative control after complete resection. D to I, Perioperative views. D, Division of the dentate ligament. E, Tracting the dentate ligament allows rotating the spinal cord and exposing the lesion on its anterior aspect. F, A nerve rootlet is dissected.Figure 186-3, cont’dG and H. The lesion is dissected en bloc. I, The final step consists in the coagulation of the draining vein. Used with permission from Hôpital Erasme, Université Libre de Bruxelles.

FIGURE 186-4 Cervical hemangioblastomas in von Hippel-Lindau disease. A, Sagittal T2-weighted magnetic resonance image (MRI). B, Sagittal T1-weighted image. C, Sagittal contrast-enhanced T1-weighted image. D, Sagittal vertebral angiogram: Two hypervascular nodules can be seen at the C3 level. E, Axial contrast-enhanced T1-weighted MRI at the C3 level.

The treatment of choice is en bloc surgical resection, achieving excellent neurological outcome. Not all patients require surgery: patients with incidental asymptomatic solitary lesions may simply be followed.²¹ Surgery is indicated as soon as symptoms develop or sequential MRI demonstrates tumor or cyst growth.¹¹ The timing of surgery remains nevertheless a matter of debate for patients with von Hippel-Lindau disease and multiple lesions.⁴² Some authors advocate operating on asymptomatic patients if radiologic progression is observed, before significant neurologic deficits occur.⁴² The follow-up of patients with von Hippel-Lindau disease must be carried out yearly by spinal and brain MRI and also for associated disease such as pheochromocytomas and for renal and pancreatic cancers.^11,⁴⁵

Cavernomas

Intramedullary cavernomas (Fig. 186-5) accounted for 3% to 16% of IMSCTs in large series.^11,^15,^24,⁴⁶ Cavernous malformations are well-delineated lesions composed of closely packed, capillary-like vessels, without intervening brain or spinal tissue.⁴⁶ Their clinical presentation may be variable: Stepwise neurologic deterioration explained by repeated hemorrhages, slow progressive deterioration induced by small hemorrhages and increasing gliosis, or acute onset with rapid or gradual deterioration due to major bleeding.⁴⁶^–⁵¹ Checking the entire central nervous system is recommended by some authors when an intraspinal cavernoma is discovered.⁴⁶ In fact as many as 40% of patients with a spinal cavernoma harbor a coexisting intracranial lesion.⁵²