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Case of the Week #334
A 70 year old woman with epilepsy presented with new onset vomiting. History and physical exam was normal, but ultrasonography revealed a round to oval heteroechoic mass near the lower pole of right kidney, in the paracaval region. An exploratory laprotomy was performed, and the mass was excised.
The mass was 7 x 6 x 4 cm, encapsulated, well circumscribed, globular, grey-white to grey-brown. The cut section revealed a variegated appearance with cystic areas, hemorrhage and areas of calcification.
Well circumscribed tumor
Cut section with variegated appearance, cystic areas, hemorrhage and calcification
Encapsulated mass with calcification
Hypercellular and hypocellular areas
Hyalinized blood vessels
Enlogated cells with cigar shaped nuclei
Hypercellular areas with palisading
Hyalinized blood vessels
Cystic areas and blood vessels
Areas of ossification
What is your diagnosis?
Retroperitoneal schwannoma (ancient)
Histologically, the tumor was well circumscribed and encapsulated, showing hypercellular and hypocellular areas. Elongated spindle shaped neoplastic cells showed tapering nuclei with nuclear palisading. Occasional areas showed enlarged, hyperchromatic nuclei with very low mitotic activity. Areas of cystic degeneration, myxoid change and ossification were noted. The spindled cells were S100 immunoreactive:
Schwannoma (neurilemoma, less commonly called neurinoma or perineural fibroblastoma) is a benign tumor arising from the nerve sheath of Schwann cells, whose etiology is still unknown (1, 2). It usually affects adults ages 20-50 years and is more common in males (3). The most common sites are head and neck and flexor surfaces of extremities. The retroperitoneum is a rare site, with an incidence of 0.3 to 3%.
Retroperitoneal schwannomas account for 1-10% of all primary retroperitoneal tumors (1), and typically have benign behavior. They are usually detected incidentally after radiological examination. Neurological symptoms are rare. Rare cases present with abdominal and lower back pain and digestive disturbances.
Pre-operative cross sectional imaging reveals a solid mass in the retroperitoneum with a few cystic areas. Although both ultrasound and computed tomography can detect the tumor, MRI allows better visualization and involvement of other organs. Radiological findings are usually non-specific and often fail to give an accurate diagnosis (4). Definitive diagnosis requires histopathological examination. CT guided biopsy can be attempted for preoperative diagnosis, but there is a risk of hemorrhage, infection and tumor seeding.
Retroperitoneal schwannomas are usually large with a glistening cut surface. Ancient schwannomas show infarct-like necrosis, cystic changes, calcification and ossification related to degeneration. Microscopically, conventional schwannomas are composed of elongated Schwann cells in hyper- and hypocellular areas, with nuclear palisading (6). The stroma contains thick-walled dilated vessels. Ancient schwannomas show nuclear polymorphism including bizarre forms with nuclear inclusions, and other secondary changes such as calcification and ossification (7).