Spinal Cord Ependymoma





Introduction


Spinal cord ependymomas are the most common intramedullary tumor in adults and the second most common tumor in children after astrocytomas.


Ependymomas typically present within the fourth decade of life and affect men more often than women. A higher incidence of these tumors occurs in patients with neurofibromatosis type II.


The presenting symptoms are often insidious and nonspecific, with the majority of patients being symptomatic for an average of 3 years before diagnosis. The most common presenting symptoms are back or neck pain (67%), sensory deficits (52%), motor weakness (46%), and bladder or bowel dysfunction (15%).


Ependymomas tend to arise centrally from the cord and to displace the surrounding neural tissue as they grow, resulting in relatively symmetric cord expansion. Mass effect on the spinothalamic tracts is thought to explain the higher proportion of patients who initially present with predominantly sensory symptoms. In general, motor symptoms are present with larger lesions.


The majority of spinal cord ependymomas occur in the cervical cord (32%) and conus medullaris and cauda equina (26.8%), followed by the cervicothoracic cord (16.3%), thoracic cord (16.3%), and thoracolumbar cord (5.1%) ( Fig. 33.1 ). Histologically, the tumors can be divided into several subtypes: papillary, clear cell, tancytic, melanocytic, and myxopapillary. The cellular subtype was removed from the WHO 2016 Classification. The myxopapillary subtype accounts for 13% to 35% of spinal cord ependymomas and typically involves the filum terminale or conus medullaris. Myxopapillary ependymomas are unique in that they can be intradural and extramedullary or be completely extradural, which is thought to be secondary to heterotopic ependymal cell rests or vestigial remnants of the distal neural tube.




Figure 33.1


Locations of spinal cord ependymoma.

(A and B) Lesions located within the thecal sac can be (A) intramedullary, as in the case of most cellular type ependymomas, or (B) extramedullary and along the cauda equine nerve roots, as in the case of most myxopapillary ependymomas. (C) More aggressive lesions can extend through the thecal sac and invade adjacent bone. (D) Very rarely, lesions can arise outside of the neural axis, as in the subcutaneous soft tissues.


Under the World Health Organization (WHO) classification system, myxopapillary tumors are categorized as grade I lesions, whereas most other subtypes are grade II lesions. An anaplastic variant is a rare, more aggressive form of the tumor and is classified as a grade III lesion.


On gross pathology, spinal cord ependymomas are soft tan- or gray-colored masses, which are usually well circumscribed with a discrete plane between the tumor and normal spinal cord. Histologically, the tumors are composed of small monomorphic cells with round or oval nuclei and rare mitoses. True rosettes are diagnostic of ependymomas but are seen less frequently than pseudorosettes, which can be present in both ependymomas and astrocytomas. Tumor cells surrounding a central ependymal canal type of lumen characterize a true rosette, whereas in a pseudorosette, the cells and their fibrillary processes surround a vascular structure ( Fig. 33.2 ).




Figure 33.2


Pathology.

(A) Gross specimen of a myxopapillary ependymoma, which was adjacent to the conus medullaris. (B) Smear preparation showing small uniform cells with oval nuclei and fine cytoplasmic processes. (C and D) True rosette formation of cells surrounding a central nonvascular lumen.

(From Ellison D, Love S, Chimelli L, et al. Non-astrocytic gliomas. In: Neuropathology: A Reference Text of CNS Pathology . 3rd ed. Edinburgh: Mosby Ltd; 2013:729–741.)










Spectrum of Disease


Intramedullary ependymomas are centrally located expansile lesions and have well-defined margins in up to 89% of cases. Myxopapillary lesions are also encapsulated and have well-defined margins when they are small. Larger lesions can appear very aggressive, with extension through the dura, and may result in osseous erosion. They can also be located extradurally or even extraneurally, with case reports describing pulmonary, sacrococcygeal, ovarian, and paraovarian locations.


The tumors usually demonstrate T1 isointense or hypointense and T2 hyperintense or isointense signal. T1-hyperintense signal is occasionally seen and reflects high protein content or blood products. Most lesions demonstrate diffuse enhancement (84%).


Syringohydromyelia is more commonly associated with ependymomas compared with other intramedullary tumors and is seen in up to 65% of cases. Cord edema surrounding the lesion is typical. Cysts are present in up to 78% to 84% of lesions, with polar cysts (62%) accounting for the majority of cystic components. Tumoral cysts occur in only 22% of ependymomas and are more likely to be associated with astrocytomas.


Hemorrhage can be seen along the superior and inferior margins of the tumor and appears as hypointense signal on T2-weighted and gradient-echo (GRE) images (cap sign). Although this finding is most commonly found in ependymomas, it is nonspecific and can also be seen in hemangioblastomas and paragangliomas. Astrocytomas do not present with a cap sign.




Mimics and Differential Diagnosis


The primary differential diagnosis for spinal cord ependymoma includes astrocytoma and hemangioblastoma. As opposed to ependymomas, astrocytomas tend to be located eccentrically within the spinal cord and hemangioblastomas are commonly located superficially along the pial surface. Astrocytomas typically show patchy, ill-defined enhancement compared with the avid, heterogeneous enhancement seen in ependymomas. Hemangioblastomas enhance in a nodular fashion and may be associated with small vascular flow voids.




Treatment and Temporal Evolution


Surgical resection is the mainstay of treatment. Because most spinal cord ependymomas are encapsulated and well delineated, gross total resection is achievable in up to 94% of cases. The 10-year disease-free survival rate after a gross total resection is between 80% and 93%.


Surgery usually involves a midline skin incision and laminectomies extending one level above and below the lesion ( Fig. 33.3 ). For larger lesions spanning multiple segments, the posterior arch is kept intact at every five or six levels to improve spine stability. The facet joints are preserved to decrease the risk of postoperative kyphosis. The dura and arachnoid are opened under microscopic magnification. The exposed tumor usually appears as a subpial discoloration. Intraoperative ultrasound can be used to identify smaller tumors or delineate solid and cystic components. The pia is either dissected in the midline or along the dorsal root entry zone and then retracted and sutured to the dura. Once the pathology has been confirmed by frozen section, the tumor is debulked centrally from the inside out using an ultrasonic device to minimize damage to the normal spinal cord. The cleavage plane between the tumor and normal spinal cord, which is present in most ependymomas, is then located and the margins of the tumor are resected. If a cleavage plane cannot be located, a less aggressive surgical approach is used to decrease risk of neurologic injury. The tumor’s vascular pedicles, which arise from the anterior spinal artery, are carefully dissected to minimize vascular injury, and the arterial feeders are cauterized.




Figure 33.3


Surgical approach. (A) Cleavage plan between the debulked tumor and the normal spinal cord. (B) Resected tumor after dissection of the vascular pedicles and cauterization of the arterial feeders. (C) Reapproximation of the spinal cord.

(From Bruneau M, Lefranc F, Balériaux D, et al. Intradural extramedullary and intramedullary spinal cord tumors. In: Ellenbogen RG, Abdulrauf SI, Sekhar LN, eds., Principles of Neurological Surgery . 3rd ed. Philadelphia, PA: Saunders; 2012:421–436.)






Adjuvant radiation therapy is used after subtotal resections and for myxopapillary or anaplastic ependymomas and results in an overall improvement in progression free survival compared to surgery alone. Repeat surgery, radiation therapy, and chemotherapy are all options for recurrent disease.


A shorter duration of symptoms is associated with overall more favorable outcomes. Upper spinal lesions have lower recurrence and mortality, which appears to be related to a higher rate of gross total resections in this area. Interestingly, there is evidence that WHO grade II lesions have a higher progression free survival compared to WHO I lesions even when accounting for extent of resection.


See also Cases 1 through 6 ( Figs. 33.4 through 33.9 ).




Figure 33.4


Case 1: A 32-year-old male who presented with neck pain and bilateral upper extremity weakness. Magnetic resonance imaging (MRI) of the cervical spine demonstrates a well-circumscribed, expansile, T2 hyperintense and T1 isointense enhancing lesion (blue brackets) in the upper cervical spinal cord with spinal cord edema (red arrow) above and below the lesion. A follow-up MRI obtained 8 months after surgery demonstrates a small resection cavity in the cervical spinal cord extending from the C2 through C4 levels but no enhancement to suggest residual or recurrent tumor. The spinal cord edema had also resolved. (A) Sagittal T2. (B) Sagittal T1. (C) Sagittal T1 with contrast. (D) Axial T2. (E) Axial T1 with contrast. (F) Sagittal T2. (G) Sagittal T1 FS with contrast.









Dec 29, 2019 | Posted by in NEUROLOGY | Comments Off on Spinal Cord Ependymoma

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