Intramedullary spinal cord tumors constitute 8% to 10% of all primary spinal cord tumors. The clinical presentation of primary spinal cord tumors is determined in part by the location of the tumor, and in nearly all clinical instances pain is the predominant presenting symptom. Motor disturbance is the next most common symptom, followed by sensory loss. Diagnosis of a primary spinal cord tumor requires a high index of suspicion based on clinical signs and symptoms, in addition to spine-directed magnetic resonance imaging.
Key points
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Identify and differentiate between the various types of intramedullary tumors including astrocytomas, ependymomas, juvenile pilocytic astrocytomas (JPAs), and hemangioblastomas.
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Determine surgical treatment options for the different types of intramedullary tumors including ependymomas, astrocytomas, JPAs, and hemangioblastomas.
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Describe the surgical procedure for minimally invasive resection of an intramedullary spinal cord tumor as well as the potential advantages.
Introduction
Primary tumors of the spinal cord are 10 to 15 times less common than primary intracranial tumors, and overall represent 2% to 4% of all primary tumors of the central nervous system (CNS). There are an estimated 850 to 1700 new adult cases of primary spinal cord tumors diagnosed each year in the United States. The histology of spinal cord tumors is similar to that of their intracranial counterparts; however, unlike primary intracranial tumors, spinal cord tumors show no association between increasing grade of malignancy and age at diagnosis. Most primary spinal cord tumors are classified as low grade (grades 1 and 2) according to the World Health Organization (WHO) pathologic classification.
Primary spinal cord tumors are divided into 3 categories based on anatomic location: intramedullary, intradural extramedullary, and extradural. Intramedullary spinal cord tumors (IMSCT) constitute 8% to 10% of all primary spinal cord tumors, with the majority comprising gliomas (80%–90%), of which 60% to 70% are ependymomas and 30% to 40% are astrocytomas. The third most common IMSCT is hemangioblastoma, representing approximately 3% to 8% of all IMSCTs, of which 15% to 25% are associated with von Hippel–Lindau (VHL) syndrome.
The clinical presentation of primary spinal cord tumors is determined in part by the location of the tumor, and in nearly all clinical instances pain is the predominant presenting symptom. In a recent series of IMSCT, pain was the most common presenting symptom (72%), manifesting as back pain (27%), radicular pain (25%), or central pain (20%). Motor disturbance was the next most common presenting symptom (55%), followed by sensory loss (39%). Diagnosis of a primary spinal cord tumor requires a high index of suspicion based on clinical signs and symptoms, in addition to spine-directed magnetic resonance imaging (MRI).
Introduction
Primary tumors of the spinal cord are 10 to 15 times less common than primary intracranial tumors, and overall represent 2% to 4% of all primary tumors of the central nervous system (CNS). There are an estimated 850 to 1700 new adult cases of primary spinal cord tumors diagnosed each year in the United States. The histology of spinal cord tumors is similar to that of their intracranial counterparts; however, unlike primary intracranial tumors, spinal cord tumors show no association between increasing grade of malignancy and age at diagnosis. Most primary spinal cord tumors are classified as low grade (grades 1 and 2) according to the World Health Organization (WHO) pathologic classification.
Primary spinal cord tumors are divided into 3 categories based on anatomic location: intramedullary, intradural extramedullary, and extradural. Intramedullary spinal cord tumors (IMSCT) constitute 8% to 10% of all primary spinal cord tumors, with the majority comprising gliomas (80%–90%), of which 60% to 70% are ependymomas and 30% to 40% are astrocytomas. The third most common IMSCT is hemangioblastoma, representing approximately 3% to 8% of all IMSCTs, of which 15% to 25% are associated with von Hippel–Lindau (VHL) syndrome.
The clinical presentation of primary spinal cord tumors is determined in part by the location of the tumor, and in nearly all clinical instances pain is the predominant presenting symptom. In a recent series of IMSCT, pain was the most common presenting symptom (72%), manifesting as back pain (27%), radicular pain (25%), or central pain (20%). Motor disturbance was the next most common presenting symptom (55%), followed by sensory loss (39%). Diagnosis of a primary spinal cord tumor requires a high index of suspicion based on clinical signs and symptoms, in addition to spine-directed magnetic resonance imaging (MRI).
Intramedullary spinal cord tumors
Astrocytomas and ependymomas represent the most common intramedullary neoplasms. It is estimated that the intracranial to spinal ratio for astrocytomas and ependymomas are 10:1 and 3:1 to 20:1, respectively (depending on the histologic variant). The clinical presentation of an intramedullary tumor is variable, but pain and a mixed sensorimotor tract disturbance (segmental sensory level, upper motor neuron signs) are usually present.
MRI of the spine is the diagnostic modality of choice; however, patients unable to undergo MRI (ie, patients with a cardiac pacemaker) may require computed tomography (CT) myelography. An intramedullary tumor is radiographically recognized by focal, and sometimes holocord, spinal cord expansion with associated T2-weighted (T2W) and fluid-attenuated inversion recovery (FLAIR) image hyperintensity, T1-weighted (T1W) hypointensity or isointensity, variable contrast enhancement, and occasional tumor-associated syrinx.
Ependymoma
Ependymomas are the most frequently encountered intramedullary spinal cord tumor in adults. Histologically there are 2 distinct pathologic types: cellular (WHO grades 2 and 3) and myxopapillary (WHO grade 1). Cellular (classic) ependymoma arises from the intraspinal canal of the cervical and thoracic cord. Myxopapillary ependymomas arise from the filum terminale and occur almost exclusively at the conus medullaris. The treatment and prognosis for spinal cord ependymomas is often excellent, as these tumors may be resected completely and in such instances manifest a low risk of recurrence.
On MRI ependymomas appear as a focal enlargement of the cord and hyperintense on T2W and FLAIR images, and hypointense or isointense to normal spinal cord on T1W images with heterogeneous contrast enhancement. These tumors may also be associated with cystic changes, hemosiderin suggestive of previous hemorrhage, and syrinx ( Fig. 1 ).
Ependymomas most often are of low grade with a benign indolent course, although malignant histologic subtypes (anaplastic ependymoma; WHO grade 3) rarely occur. Surgery is the most effective treatment, with complete surgical resection yielding reported local control rates of 90% to 100%, although gross total resection is not achieved in most patients. Intraoperative monitoring of motor and somatosensory evoked potentials are often used to assist in achieving a more safe and complete resection. Involved-field external beam radiotherapy at a dose of 45 to 54 Gy is indicated for partially resected or biopsied WHO grade 2 ependymomas or malignant WHO grade 3 tumors. Overall, spinal cord ependymomas are associated with prolonged progression-free and overall survival, with a median of 82 months and 180 months, respectively.
Astrocytoma
Approximately 40% of IMSCTs are astrocytomas. The majority (75%) are low-grade (WHO grade 2) fibrillary astrocytomas with 5-year survivorship exceeding 70%. Histology is the most important prognostic variable. Juvenile pilocytic astrocytoma (JPA) is a low-grade (WHO grade 1) variant that more commonly presents in younger patients. High-grade spinal cord gliomas (WHO grades 3 and 4, 25%) are less common and associated with a poor survival. Regardless of WHO grade, spinal cord astrocytomas are infiltrative and associated with poorly characterized boundaries, and consequently are typically biopsied only. However, a recent case report of cordectomy yielded survival of longer than 15 months in one patient.
Astrocytomas appear on MRI as fusiform expansion of the cord with an indistinct and, occasionally, cystic component. Associated edema or syrinx (seen in 40%) may be present. The tumor is hypointense to isointense on T1W images and hyperintense on T2W and FLAIR images, with variable contrast enhancement. In general, the distinction between astrocytomas and ependymomas by MRI is not always possible ( Fig. 2 ).
Initial treatment consists of maximal safe surgical resection or biopsy followed by observation or external beam radiotherapy. Because spinal cord gliomas are infiltrative, gross total resection is rarely accomplished (in approximately 12% of WHO grade 2 and 0% of grade 3 or 4 astrocytomas). The optimal extent of surgical resection and need for postoperative radiotherapy is controversial. Tumor histology, extent of resection, and functional status at time of presentation seem to be the primary determinants of outcome. Nonetheless, radiotherapy is indicated for patients with high-grade histology, tumors in which a substantial resection cannot be performed, biopsied-only tumors, and those with progressive disease. Though rare in adults, most spinal cord JPAs can occasionally be completely resected (up to 80%).
Hemangioblastoma
Hemangioblastomas, the third most common IMSCT, are rare vascular tumors that occur as a solitary tumor or as part of VHL syndrome. Approximately 10% to 30% of patients with hemangioblastoma of the spinal cord have VHL syndrome, an autosomal dominant disorder caused by a deletion on chromosome 3p. Other tumors associated with VHL include retinal hemangiomas, renal and pancreatic cysts, pheochromocytomas, and renal cell carcinomas. Regardless of whether hemangioblastoma occurs as part of the VHL syndrome or solitarily, the clinical and histopathologic characteristics are identical. There is a male predominance, and presentation is usually in the fourth decade.
Most hemangioblastomas arise from the dorsal or dorsolateral portion of the spinal cord. As such, presenting symptoms are usually sensory, especially slowly progressive proprioception deficits. There may also be other long tract signs and radicular symptoms. Rarely, patients present with subarachnoid or intramedullary hemorrhage.
On MRI, the hemangioblastomas appear as a homogeneously enhancing hypervascular nodule with associated cyst or syrinx and peritumoral edema. Spinal angiography demonstrates enlarged feeding arteries, intense nodular stains, and early draining veins. Hemangioblastoma can be differentiated from ependymoma by the vascular abnormalities on MRI, and the presence of tumor hypervascularity with feeding arteries and draining veins on a spinal angiogram if performed. Hemangioblastoma is differentiated from a spinal cord vascular malformation by associated syrinx and tumor enhancement on MRI ( Fig. 3 ).
Surgical resection is the primary treatment. There are often well-defined margins allowing for a complete resection. Excessive intraoperative bleeding that obscures the operative field is the limiting factor for subtotal resection. In contrast to posterior fossa hemangioblastomas, preoperative embolization is usually not performed, as complications have been reported. Serial MRI should be obtained because de novo lesions can appear in patients with VHL. There is a limited role for radiotherapy, and experience with chemotherapy is almost nonexistent. Stereotactic radiosurgery is an option for patients with recurrent or unresectable tumors.
Ganglioglioma
Ganglioglioma is a glial-neuronal tumor that usually occurs in the brain, but may arise from the intramedullary spinal cord. The tumor is typically slow growing, but rarely may have an aggressive course. Adult cases of spinal cord ganglioglioma are rare, and paraparesis and radicular pain are the most common presenting symptoms.
On T1W MRI the tumor is hypointense or has mixed signal characteristics, and has homogeneous or heterogeneous hyperintensity on T2W/FLAIR images, with variable contrast enhancement. Tumor cysts, scoliosis, and bone erosion/scalloping may be present.
Maximal surgical resection is the optimal treatment for spinal cord gangliogliomas. Complete or near complete resection is associated with excellent long-term survival and minimal morbidity. Postoperative radiotherapy is not recommended, even in patients who undergo a subtotal resection. Despite the apparent benign nature, the progression-free survival rate in the largest case series (56 pediatric patients) was only 67%. Rarely, there is transformation to a higher-grade tumor (ie, anaplastic ganglioglioma).
Lymphoma
Primary CNS lymphoma rarely (<1% of all CNS lymphomas) presents as an isolated spinal cord intramedullary tumor. On MRI, lymphoma appears as single or multifocal, ill-defined T2W/FLAIR hyperintense lesions with homogeneous contrast enhancement on T1W images. Because of high cell tumor density, diffusion-weighted MRI often demonstrates restriction and a correspondingly high signal, that is, hyperintensity. Following histologic diagnosis, a careful search for other sites of CNS disease (including slit-lamp eye examination, brain MRI, total spine MRI, and cerebrospinal fluid [CSF] flow cytometry/cytology) should be performed. Because CNS lymphoma is a diffuse disease most often affecting the entire neuraxis, treatment should include high-dose methotrexate-based chemotherapy similar to regimens used to treat CNS lymphoma involving the brain.
Germinoma
Several investigators have described cases of primary intramedullary spinal cord germinoma. Age at presentation is between 10 and 40 years old. Craniospinal axis imaging and CSF cytology should be obtained to look for other sites of disease. Because germinoma is usually radiosensitive and chemosensitive, treatment includes biopsy followed by radiotherapy alone or in combination with platinum-based chemotherapy.
Melanoma
Melanoma can arise and be isolated to the intramedullary spinal cord region; numerous cases have been reported. Clinical presentation is similar to that of other intramedullary tumors, but often evolves more rapidly than ependymomas or astrocytomas.
On MRI, melanoma is usually hyperintense on T1W images, isointense or hypointense on T2W/FLAIR images, and with mild contrast enhancement. Intratumoral hemorrhage is common at presentation, and may lead to the erroneous diagnosis of cavernous angioma or other vascular malformation. The MRI features are variable depending on intratumoral bleeding and melanin content. Because there is no straightforward MRI method to differentiate primary spinal cord melanoma from metastatic tumor, a careful examination of skin, squamous mucosa, and eyes should be performed as well as contrast-enhanced CT imaging of the chest, abdomen, and pelvis.
Surgery establishes the diagnosis and may provide long-term palliation if the tumor is resected completely. As complete image-verified resection is rarely achieved, most patients receive postoperative radiotherapy.
Others
Other rare primary IMSCTs include primitive neuroectodermal tumor (PNET), paraganglioglioma, teratoma, dermoid cyst, epidermoid cyst, lipoma, and hamartoma. Treatment following maximal safe resection is similar to that of intracranial counterparts, and in most instances surgery suffices as primary therapy (PNET being the exception).
Surgical treatment of intramedullary tumors
The treatment of intramedullary spinal cord tumors has been largely based on open surgical biopsy or resection if possible. Successful surgical resections with good clinical outcomes have been reported in the literature with traditional open surgery. However, surgical morbidity should also be considered when resecting these lesions.
Open surgical intervention requires adequate exposure with removal of the posterior spinal elements. These structures are also important in maintaining alignment of the spinal column. Extensive removal of the posterior elements can be associated with increased pain and increased blood loss, and can lead to worsening kyphotic deformities of the spine. This anomaly is more pronounced in the cervical spine, but can also occur in the thoracic spine. It has been reported in the literature that there was an increased risk of kyphosis in the pediatric population after patients underwent surgeries that required greater than 3 levels of laminectomy for the intradural tumor resection. Therefore, some neurosurgeons perform laminoplasties in the pediatric population to decrease the risk of postsurgical kyphotic deformity as the patient ages.
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