Spinal paraganglioma (WHO grade I)
Paraganglioma is a rare tumor of the dispersed neuroendocrine system, arising in specialized neural crest cells associated with autonomic ganglia (1-4). It affects a variety of anatomic sites, including the head and neck for carotid body tumors, the mediastinum, and the retroperitoneum. When occurring as a primary tumor involving the central nervous system, the cauda equina is the most common site.
As paraganglion cells are not typically observed in the cauda equina, the histogenesis of this tumor may pose as a subject of debate (3). While some have favored an origin from paraganglion cells associated with regional autonomic nerves and blood vessels, others postulate that peripheral neuroblasts can undergo paraganglionic differentiation to ultimately give rise to this tumor (3).
As an uncommon spinal lesion, experiences with this tumor are relatively rare. Back pain typically leads to imaging, revealing an intradural tumor in the cauda equina region that invokes a radiographic differential diagnosis that includes peripheral nerve sheath tumor such as schwannoma or neurofibroma, meningioma, and ependymoma (1,3,4). While the histologic features of many paragangliomas are classic, with neoplastic features showing compact nested (Zellballen) architecture and a stippled chromatin pattern generally associated with neuroendocrine differentiation, cases have described ependymoma-like histology (1,2) and gangliocytic differentiation (2). In fact, one reported case of spinal paraganglioma had initially been diagnosed as an ependymoma (1). As such, H&E evaluation alone may give rise to a differential diagnosis that is similar or identical to the radiographic impression.
However, the histologic differential diagnosis of ependymoma, meningioma, peripheral nerve sheath tumors, and paraganglioma can readily be resolved by immunohistochemistry (3). Reactivity for neuroendocrine markers (synaptophysin, chromogranin, CD56) will lead in the direction of paraganglioma, while absence of reactivity for the epithelial membrane antigen (EMA) will argue against meningioma and ependymoma. Demonstration of reactivity for S-100 in scattered background sustentacular cells, with absence of diffuse reactivity in neoplastic cells, further supports a diagnosis of paraganglioma, while arguing against the possibility of a peripheral nerve sheath tumor or a glial neoplasm such as ependymoma (3). Immunohistochemistry was of especially high value in this particular case, as the tumor demonstrates pseudorosette-like foci reminiscent of ependymoma.
As a slow-growing, generally well-demarcated tumor, spinal paragangliomas are assigned a WHO grade of I (3). An estimated 4% of cases recur following gross total resection, and metastasis outside of the CNS is rare. Currently, the clinical behavior of this tumor cannot be predicted based on histologic features or criteria (3). Nevertheless, as paragangliomas may arise in other anatomic sites and metastasize to the CNS, prior to rendering a diagnosis of spinal paraganglioma of WHO grade I, the likelihood of tumor occurring elsewhere in the body should be excluded.
In the present case, a maximal safe resection was pursued. Following surgical debulking, the patient underwent radiation therapy to address the remaining tumor.
Contributed by Brian H. Le, MD and Stamatios G. Psarros, MD