Peripheral primitive neuroectodermal tumor of cauda equina: A report and review of literature
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.232344
Source of Support: None, Conflict of Interest: None
Peripheral primitive neuroectodermal tumor (PNET) has been reported, although rarely, as a cauda equina tumor. It is more aggressive than the common tumors of cauda equina viz. ependymoma and schwannoma. This is a report of a 65-year old man who had a PNET of the cauda equina.
The patient presented with low backache and pain radiating to both lower limbs. There was severe pain on walking, which was progressive. At the time of presentation, he could not walk at all and was bedridden. The straight leg raising test was positive at 60° on the left side. Magnetic resonance imaging (MRI) of the lumbosacral spine showed a well-defined oval-shaped lesion in the intradural space at the L2 vertebral level measuring 15 mm × 12 mm × 10 mm [Figure 1]a. The lesion exhibited intermediate signal on T1-weighted and T2-weighted sequences with intense homogeneous enhancement on contrast study [Figure 1]b. It also caused displacement and compression of the nerve roots and occupied the spinal canal completely.
An L2 laminectomy was done under general anesthesia in prone position. The bulging dura matter was opened. A yellow pink nodular tumor was seen amidst the nerve roots of the cauda equina [Figure 2]a and [Figure 2]b. The tumor was seen to be attached to two roots on either side and was dissected from the roots. The tumor was excised en toto. Bleeding was controlled using surgicel, and the dura was closed. Postoperative MRI showed complete excision of the tumor [Figure 2]c. He was ambulated and was relieved of his pain. Motor and sensory examination did not reveal any deficits.
Histopathological examination showed an encapsulated nodule composed of a malignant neoplasm showing a diffuse infiltrate of round cells with large nuclei, coarse chromatin, prominent nucleoli, and scanty cytoplasm [Figure 3]a. Atypical mitoses and focal areas of necrosis were noted. Immunohistochemistry was done. CD 99 (cluster of differentiation 99) had a strong and membranous positivity [Figure 3]b. Neuron-specific enolase and periodic acid Schiff tests were positive [Figure 3]c and [Figure 3]d. Vimentin was weakly positive. There was strong nuclear positivity for FLI (friend leukemia insertion)-1 [Figure 4]. The Ki-67 index was 20%. LCA (leukocyte common antigen), CD20 (cluster of differentiation 20), EMA (epithelial membrane antigen), Synaptophysin, GFAP (glial fibrillary acidic protein), Pan CK (pan-cytokeratin), CD138 (cluster of differentiation 138), Mum1(multiple myeloma oncogene 1), MPO (myeloperoxidase), and S100 were negative. A diagnosis of PNET was given. MRI screening of the whole body was done which was normal. Repeat MRI after 2 months did not show any recurrence. He is on follow-up for the last 8 months.
The most common tumor of cauda equina is myxopapillary ependymoma. The differentials reported are nerve sheath tumor, meningioma, paraganglioma, intradural metastases, lymphoma, other varieties of ependymoma, subependymoma, astrocytoma, ganglioglioma, hemangioblastoma, and PNET.PNET is rare in the cauda equina. It is common in the young and rare in the elderly patients. For spinal PNET, the common sites are the filum terminale and cauda equina.
The term PNET was coined by Hart and Earle in 1973 to describe a predominantly undifferentiated tumor of the cerebrum. PNET is a small round cell tumor of neural crest origin, typically seen in the second or third decades of life. It is a highly malignant tumor, sharing morphological, histochemical, and immunogenetic features with Ewing's sarcoma. Primary spinal PNET is diagnosed when one or more histopathologically proven PNET lesions are present in the spinal axis, in the absence of a lesion in the brain. Secondary spinal PNET occurs due to subarachnoid seeding from a primary cranial PNET. These are aggressive lesions characterized by a rapid growth, a short duration of symptoms, and tumor recurrence in most patients.
PNET histologically appears as a predominantly undifferentiated small, blue, round cell tumor with hyperchromatic nuclei, scanty cytoplasm, and frequent mitotic figures. PNETs are classified into the central type and the peripheral type based on their origin. Central PNET has a central nervous system (CNS) origin and peripheral PNET has its origin outside the CNS. Peripheral PNET (pPNET) strongly expresses glycoprotein CD99. PNETs can be differentiated from other small round cell tumors viz. lymphoma, Ewing's sarcoma (ES), rhabdomyosarcoma, and small cell carcinoma by neural differentiation., ES/pPNETs are characterized by translocations that occur in 95% of the tumors. This translocation joins the Ewing's sarcoma gene (EWS) located on chromosome 22 to an ets family gene; either the friend leukemia insertion (FLI) 1 located on chromosome 11, t(11; 22) in 85% of cases, or the ets-related gene (ERG) located on chromosome 21, t(21; 22) in 10% of cases. Immunohistochemical detection of FLI-1 may be valuable in confirming the diagnosis of ES/PNET in cases in which molecular genetic evaluation is not feasible.
The present treatment of spinal PNET consists of local control in the form of surgery or radiotherapy combined with systemic control with chemotherapy.
There are only few reports of PNET of the cauda equina. Mc Dermott et al., reported the case of a 47-year old man who had an unresectable cauda equina PNET for whom biopsy and radiotherapy were done; however, the patient died 1 year and 2 months later. Akyuz et al., reported the case of a 31-year old female patient with a PNET of the cauda equina showing intracranial seeding 6 months after surgery. Dhatt et al., reported the case of a 24-year old male patient with an L5 vertebral PNET with cauda equina syndrome. Fabre et al., reported the case of a 70-year old man with a cauda equina PNET. Isotalo et al., described pathological features of PNET of the cauda equina occurring in a 52-year old man. Jitendra et al., reported a cauda equina tumor in a 11-year old boy, which turned out to be a PNET. Near total removal, radiation, and chemotherapy were done. Kumar et al., reported an intracranial metastasis manifesting as a parietal tumor in a 22-year old female patient who had a cervicothoracic spinal PNET. Metastasis occurring 10 years after the initial diagnosis in a spinal PNET has been reported by Gollard et al. Spinal PNET that had an initial chronic inflammatory demyelinating polyneuropathy-like presentation in a young boy was reported by Chan et al. Intramedullary PNET presenting with rapidly-progressive cauda equina syndrome in a 39-year-old male patient who underwent subtotal resection was reported by Tsutsumi et al.
Most cases in the literature are of aggressive nature among young and middle-aged individuals. The uniqueness of our case is that the patient was 65-year old and complete excision was achieved. Another peculiarity is that the novel immunohistochemical marker FLI-1 was positive.
PNET should also be thought of in the differential diagnosis of a cauda equina tumor. It is a malignant tumor with a high chance of recurrence. Complete excision should be done if possible. Local control and systemic chemotherapy are needed.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]