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Unusual Intradural Location of a Rare Pilomyxoid Astrocytoma of the Entire Spinal Canal 2006

General Spine

Michal M Mendiratta-Lala, M.D., Non ASSR Member
Horia Marin, M.D., Non ASSR Member
Suresh C Patel, M.D., Non ASSR Member
Rajan Jain, M.D., Non ASSR Member

Excerpta Extraordinaire

Excerpta

Pilomyxiod astrocytoma(PMA) is a rare sub-type of pilocytic astrocytoma, commonly originates in the hypothalamus or optic chiasm and presents in infants with only three cases of PMA of the spinal cord reported in children less than eight years of age. This is a rare case report of PMA presented as an intradural not an intramedullary mass involving the entire spinal canal, in a 34 year old female. The intradural tumor was located dorsal to the entire spinal cord was hypointense on T1 weighted images and extremely bright on T2 weighted images. The intradural PMA avidly enhanced with contrast material and filled the entire thecal sac of the spinal canal including the lumbar-sacral spinal canal distal to the conus medullaris. PMA is composed of glial cells within a monophasic pattern in an extensive myxoid/mucinous background. The myxoid/mucinous background is probably the reason for extreme brightness on T2Weighted images. PMA lacks Rosenthal fibers and rarely have eosingophillic granular bodies with neoplastic cells radiating from vessels producing an angiocentric pattern. The histologic features differentiates it from the pilocytic astrocytoma. Due to aggressive characteristics, PMA is associated with shorter progression free survival rates.

Purpose

Spinal intradural extramedullary tumors account for two-thirds of all intraspinal tumors, and the most common are nerve sheath tumors. Spinal cord astrocytomas are an infrequent lesion, which rarely occur after 60 years of age, and are the most frequent histologic type of spinal cord tumor in the pediatric population. (1) Spinal cord astrocytomas are most commonly intradural intramedullary lesions. Unlike astrocytomas in the brain, spinal cord astrocytomas are usually low grade lesions. (1) There are subtypes of astrocytomas, the most common are pilocytic, fibrillary, and anaplastic. Recently, a rare pilomyxoid variant has been described, known as pilomyxoid astrocytoma (PMA). (in contrast to the biphasic pattern of pilocytic astrocytoma (PA), appears as monomorphous piloid cells in a loose fibrillary and myxoid background, without Rosenthal fibers.(2)) While the most common origin is in the hypothalamus or optic chiasm, and the most frequent age group is in infants, PMA in the spinal cord has been rarely described, and only in children (3.4). In this report, we describe an unusual case of PMA located extensively within the spinal canal as an intradural extramedullary lesion in a young adult.

Methods & Materials

Case Report:

A 32 year old female presented with a three-week history of progressive neck and back pain associated with nausea and vomitting. She also had weakness in both upper and lower extremities with 4/5 motor strength. Her examination revealed hyperreflexia of the right knee, with downgoing plantar reflexes bilaterally. She had paresthesias in the C6-T1 dermatomes, with intact mental status and cranial nerves.

MRI of the entire spine confirmed an intradural extramedullary lesion, from the C5 level inferiorly into the thoracic region, causing anterior spinal cord compression, occupying most of the thecal sac, and with a small syrinx cavity at the C5 level. There was extensive post-contrast enhancement, with some central areas of non-enhancement. There was also scalloping of the posterior margin of the vertebral bodies.

Because of the associated cervical myelopathy, she underwent bilateral laminectomy at C5-T1, with durotomy and partial resection of the intradural extramedullary tumor, for cord decompression. The tumor appeared gelatinous and fibrous in nature, and aggressively herniated out upon opening of the dura mater. The tumor was extensively removed in the exposed region, with piecemeal removal of the tumor from the lateral gutters. Formalin fixed pathologic analysis described an astrocytic neoplasm, consistant with a pilocytic variant, with an MIB-1 index of 3%.

Post-surgically, the patient began to develop increasing lower extremity weakness, with muscle strength 4/5 pre-operatively to 0-1/5 post-operatively, as well as development of bladder dysfunction. Repeat MRI demonstrated the initial post surgical changes, with residual tumor visualized, and anterior compression of the spinal cord. The patient returned to the OR for decompression of the lower thoracic spine, with intradural debulking of the tumor and duroplasty. The entire tumor could not be excised because it was extremely adherent to the spinal cord and the nerve roots more distally.

Formalin fixed pathologic analysis was performed for a second time, and showed neoplastic proliferation of glial cells, with pleopmorphic nuclei and piloid fibrillary processes. There was hyalinized vessels throughout, with an abundance of myxoid/mucinous matrix, in a monophasic background, consistant with the pilomyxoid variant of pilocytic astrocytoma.

Radiation therapy from T1-L3 levels were initiated, and currently, patient is still undergoing XRT. Post-operatively, she continued to have plegia of her lower extremities, and spinal cord rehabilitation was intitiated.

Results

Discussion:

Spinal cord astrocytoma is an uncommon finding, and only represents 6-8% of spinal cord tumors (7), most of which are intradural intramedullary. Most are pilocytic astrocytomas (PA), as opposed to nonpilocytic (fibrillary, anaplastic) (7). Recently, a subgroup of pilocytic astocytoma with similar histologic features, but with other associated findings and outcomes, was identified, known as pilomyxoid astrocytoma (PMA). Most reported PMA's occur in the hypothalamic/chiasmatic region, and occurs within the first four years of life. Komotar et al recently described 3 cases of PMA in the spinal cord, however, all in children less than 8 years of age (4). The mean age of diagnosis of PMA is 18 months, although it can present in early childhood (4, 5, 12).

The usual clinical presentation is variable, and can progress over a time span of months to years. Pain is the earliest and most frequent complaint (1). Sensory disturbances, such as dysthesias or loss of sensation are also common (1). Weakness, spastisity, and loss of bowel and bladder function occurs late (15).

PMA is usually well-circumscribed with solid or cystic components and rarely has calcifications (5). The lesions are isointense on T1 weighted MRI and hyperintense on T2 weighted MRI, with variable enhancement post-gadolinium. There may be associated peritumoral edema, mass effect, and necrosis (5). Radiographic findings of PMA are similar to that of PA (5).

Therefore, the diagnosis of PMA is usually made from the histological findings (5). PMA is composed of glial cells within a monophasic pattern in an extensive myxoid/mucinous background. This is in contrast to pilocytic astrocytomas, which are found in a biphasic background. PMA usually lacks Rosenthal fibers, and rarely have eosinophillic granular bodies, unlike PA. Often the neoplastic cells radiate from vessels, thus producing an angiocentric pattern, and vaguely resemble perivascular rosettes (2,4,5,12). This is irregular and fibrillar when compared to the perivascular rosettes of ependymomas (12). There is occasional infiltration of the tumor into the surrounding normal parenchyma, with only a few described cases of mitotic figures (2, 12). Finally, a few cases have shown necrotic foci (12).

Tumor location has obvious implications for surgical management and outcome. Treatment options for PMA include tumor resection, radiation therapy, and chemotherapy. Resection can pose a challenge because of the extensive infiltration usually seen with PMA's, and therefore, most cases result in subtotal resection. There is generally a poorer prognosis in patients who undergo more aggressive resection, versus those with less resection, specifically in patients with PA (7). This, however, is not reported in patients with PMA because of the rarity of this tumor subtype. Prognosis is therefore partially dependent on long-term behavior of the partially resected tumor. Unfortunately, PMA's are more aggressive than PA's, and can therefore have a worse prognosis, although better than that of infiltrating PA's (4).

The median post operative follow-up is 14 months in infants and children, with the majority of cases presenting with local recurrence and a few with CSF dissemination of the tumor (12). PA has a lower rate of recurrence, with rare reports of CSF spread (2, 14). According to Komotar et al, patients with PMA have a shorter overall survival and progression free survival times than patients with PA.

From studies to date, PMA appears to be a more aggressive subtype of PA's. Some reasons include: 1. they recur sooner and more frequently than PA's (2,5,6,12); 2. CSF dissemination is more common (2,5,12); 3. Necrosis of the tumor, which occurs more frequently in rapidly growing tumors, occurs in PMA's, as opposed to PA's (6,12); 4. PMA's are more likely to invade surrounding structures (2,6); 5. Patients with PMA's experience a shorter progression free survival than patients with PA's (2).

Another unusual finding in pilomyxoid astrocytomas, is anaplastic change of the initial or recurring tumor, after resection, chemotherapy, or radiation therapy. The anaplastic change results in a more benign tumor, although this has only been reported in a few cases (2,3,12). This may suggest maturation of the tumor, however, the clinical significance is unclear given the rarity of this finding.

This case is unusual for a variety of reasons. First, it is uncommon to find an astrocytoma in an intradural extramedullary location. Second, there are only 3 other reported cases of PMA within the spinal cord. Finally, none of the reported cases of PMA occur in patients over the age of 8, and this patient was 32 years old.

Conclusion

Pilomyxoid astrocytomas are a subtype of the more frequent pilocytic astrocytomas, with distinct histologic features and a more aggressive subtype, most commonly occurring in younger ages. Because it is a more aggressive tumor, surgical resection is often incomplete, and therefore requires adjuvant treatment. This neoplasm is generally associated with shorter progression free survival. Better identification and recognition of these tumors may help in improved understanding of treatment options and outcomes.

References

Financial Disclosures: None

1. Houten JK, Cooper PR. Spinal cord astrocytomas: presentation, management and outcome. J Neurooncol. 2000 May;47(3):219-24. Review.
2. Komotar RJ, Burger PC, Carson BS, Brem H, Olivi A, Goldthwaite PT, Tihan T. Pilocytic and Pilomyxoid Hypothalamic/Chiasmatic Astrocytomas, Neurosurgery. 2004; 54: 72-9.
3. Zhongxin Yu, M.D., M.S.1, Gregory N. Fuller, M.D., Ph.D.2 An 18 month-old girl with a hypothalamic tumor. E-Reference: Case 503-1 Department of Pathology, University of Oklahoma Health Science Center
4. Komotar RJ, Carson BS, Rao C, Chaffee S, Goldthwaite PT, Tihan T. Pilomyxoid astrocytoma of the spinal cord: report of three cases. Neurosurger. 2005; 56:191.
5. Komotar RJ, Mocco J, Jones JE, Zacharia BE, Tihan T, Feldstein NA, Anderson RC. Pilomyxoid astrocytoma: diagnosis, prognosis, and management. Neurosurg Focus. 2005 Jun 15;18(6A):E7.
6. Fernandez C, Figarella-Branger D, Girard N, Bouvier-Labit C, Gouvernet J, Paz Paredes A, Lena G. Pilocytic astrocytomas in children: prognostic factors--a retrospective study of 80 cases. Neurosurgery. 2003; 53: 544-53.
7. Minehan KJ, Shaw EG, Scheithauer BW, Davis DL, Onofrio BM. Spinal cord astrocytoma: pathological and treatment considerations. J Neurosurg. 1995 Oct;83(4):590-5.
8. Epstein FJ, Farmer JP, Freed D. Adult intramedullary spinal cord ependymomas: the result of surgery in 38 patients. J Neurosurg. 1993 Aug;79(2):204-9.
9. Innocenzi G, Salvati M, Cervoni L, Delfini R, Cantore G. Prognostic factors in intramedullary astrocytomas. Clin Neurol Neurosurg. 1997 Feb;99(1):1-5.
10. Houten JK, Weiner HL. Pediatric intramedullary spinal cord tumors: special considerations. J Neurooncol. 2000 May;47(3):225-30. Review.
11. Giannini C, Scheithauer BW, Burger PC, Christensen MR, Wollan PC, Sebo TJ, Forsyth PA, Hayostek CJ. Cellular proliferation in pilocytic and diffuse astrocytomas. J Neuropathol Exp Neurol. 1999 Jan;58(1):46-53.
12. Tihan T, Fisher PG, Kepner JL, Godfraind C, McComb RD, Goldthwaite PT, Burger PC. Pediatric astrocytomas with monomorphous pilomyxoid features and a less favorable outcome. J Neuropathol Exp Neurol. 1999; 58:1061-8.
13. Arslanoglu A, Cirak B, Horska A, Okoh J, Tihan T, Aronson L, Avellino AM, Burger PC, Yousem DM. MR imaging characteristics of pilomyxoid astrocytomas. Am J Neuroradiol. 2003; 24:1906-1908.