DIAGNOSIS: Paraganglioma of the Filum Terminale
Paragangliomas are neoplasms of paraganglia, which are broadly divided into two categories: sympathetic and parasympathetic, and include the adrenal medulla and periaortic organs of Zuckerkandl. Paraganglia are composed of neuroendocrine cells (derived from the neural crest) and supporting cells or "sustentacular" cells. Older, more complicated nomenclature for tumors derived from these organs has been supplanted by the current unitary approach taken by the World Health Organization (WHO) which terms all tumors of paraganglia as paragangliomas, with the exception of pheochromocytoma which has been retained for tumors of the adrenal medulla. Paragangliomas occur widely throughout the body and belong to a larger category of neuroendocrine neoplasms known by the term APUD (amine precursor uptake and decarboxylation), referring to their ability to secrete biogenic amines.1 Such products include epinephrine, norepinephrine, dopamine, serotonin, and peptides or proteins including enkaphalins, ACTH, and somatostatin.2,3 Grossly, paragangliomas are encapsulated, soft, and dark red. Classic histological features include small lobules of cells (žzellballenÓ) with granular eosinophilic cytoplasm, žsalt and pepperÓ chromatin, an orderly relationship to blood vessels (which are abundant and often sinusoidal), and S100 positive sustentacular cells.4 Secretory granules can be identified with the Grimelius stain or immunohistochemical methods to detect chromogranin or synaptophysin. Neurosecretory granules can also be seen by electron microscopy.
Paragangliomas of the central nervous system are parasympathetic, derived from parasympathetic "chief" cells. They occur most frequently within the intradural filum terminale, but also arise in spinal and cranial nerve roots. Published series of paragangliomas of the filum terminale have shown an average age at presentation of 48 and 51 years, with a slight male predominance.5,6 Within the central nervous system they are classified as grade I tumors.7 Since they have little secretory activity, symptoms are usually caused by tumor mass effect. Complete surgical excision is curative, but malignant examples have been reported.
The differential diagnosis for a sausage-shaped tumor of the filum terminale includes: schwannoma, myxopapillary ependymoma, paraganglioma, and rarely meningioma. All, when occurring within the filum terminale, appear as discrete, enhancing, sausage-shaped masses. Schwannomas, universally S100 positive, are biphasic spindle cell neoplasms with Antoni A and B areas and verocay bodies. The myxopapillary ependymoma is common in the filum terminale and rarely reported elsewhere. It shows the same propensity for perivascular pseudorosette formation as other ependymomas, but in addition, features large perivascular collars of mucin and PAS-positive bodies termed žballoonsÓ. The perivascular orientation of cells in a myxopapillary ependymoma can make it difficult to distinguish from paraganglioma, which also shows an orderly relationship of tumor cells to blood vessel walls and occasional pseudopapillary patterns. Immunohistochemical stains for synaptophysin and glial fibrillary acidic protein should serve to distinguish paraganglioma from ependymoma. Meningiomas, usually EMA positive, display a variety of histologic patterns, occurring most frequently as transitional or meningotheliomatous forms, with whorls of uniform meningothelial cells and psammoma body formation.