Giant Schwannoma In The Pelvic Retroperitoneum
Correspondence Address :
Dr.Leo Francis Tauro,Departmentof General Surgery,Fr. Muller Medical College Hospital,Kankanady,Mangaloreâ€“575002 (D.K.),Karnataka.(India)Ph.No:Hosp:(0824)2436301,Res(0824)-2224911 E-Mail: email@example.com
Schwannoma (neurilemmoma) is a peripheral nerve sheath tumour and commonly occurs on the head, neck and trunk. Giant schwannoma is rarely located on the retro peritoneum and the pelvic cavity. The majority of symptoms caused by the tumour are due to its mass effect. Surgical resection is enough to treat the tumour. Schwannoma is usually a benign tumour. Its malignant transformation is usually very rare. We report a 60 year male patient with giant pelvic schwannoma which presented with urinary symptoms.
Schwannoma, retroperitoneal space, neurilemmoma, computed tomography. (CT).
Schwannoma (neurilemmoma) is a peripheral nerve sheath tumour and commonly occurs on the head, neck and trunk. Giant Schwannoma is rarely located on the retro peritoneum and the pelvic cavity. The majority of symptoms caused by the tumour are due to its mass effect. Surgical resection is enough to treat a tumour(1). Schwannoma is usually a benign tumour. Its malignant transformation is usually very rare(2). We report a 60 year old male patient with giant pelvic schwannoma which presented with urinary symptoms.
A 76 year â€“ old â€“ male patient presented with a 6 month old abdominal mass with abnormal urinary frequency and urgency, and burning micturition for 1 week. There was no history of bowel disturbances. On general physical examination, no abnormality was detected. Abdominal examination revealed a non tender, firm, fixed, retroperitoneal mass of 12x14 cm size with smooth surface and well defined borders, in the supra pubic region extending into the pelvis. The inferior border was merging in to the pelvic cavity. There was no hepatosplenomegly. Rectal examination revealed prostatomegaly.
His routine haematological investigation and urine analysis were within normal limits. His blood urea, serum creatinine and liver function tests were within normal limits. His serum prostate specific antigen (PSA) value was 8.40 ng/ml. Abdominal ultrasonography revealed a complex mass measuring 14x10 cms in the pelvis with hyper echoic areas. Bilateral hydronephrosis was noted. CT scan was suggested for further evaluation. CT scan of abdomen revealed a large retroperitoneal, heterogeneously enhancing complex cystic lesion measuring 10x13 cms. It was located predominantly at the right side of the pelvis, extending into the abdomen up to the level of aortic bifurcation. No calcified areas were detected. The lesion was displacing the bladder postero- inferiorly and the bowel loops laterally. The right ureter was displaced medially. Prostatomegaly was present (Table/Fig 1), (Table/Fig 2). Ultra sound guided FNAC of the mass revealed vascularised fibro- collagenous tissue, without any evidence of malignancy.
The abdomen was opened through the lower midline incision. A huge retroperitoneal mass was noted in the pelvis, extending upwards, without any posterior infiltration into the surrounding structures. The peritoneum over the mass was opened, and complete excision of the mass was done, with blunt dissection.(Table/Fig 3)and (Table/Fig 4) Histopathological examination of the resected specimen revealed a capsulated mass showing cellular areas with spindle shaped cells, in a pallisading pattern. Occasionally, vero cay bodies were seen. Less cellular areas showed scattered spindle cells. Areas of necrosis and degeneration were also seen. These features were suggestive of schwannoma (Table/Fig 5). The post operative period was uneventful. The patient was asymptomatic on 6 months follow up.
Benign nerve sheath tumours are typically divided into two groups: schwannomas and neurofibromas, of which the former are the more common. Schwannomas most frequently present in patients aged 20 to 50 years, and more frequently in men than in women. They comprise 5% of all benign soft tissue tumours and have a predilection for the head and neck and flexor surfaces of the upper and lower extremities. Deeply seated shwannomas predominate in the posterior mediastinum and retro peritoneum (2). Shwannomas are almost invariably slow growing, non - aggressive neoplasms, and they are solitary in the vast majority of cases; 5% to 18% of tumours are associated with the neurofibromatosis type(3). in which case lesions may be multiple, and often plexiform. Malignant transformation is very rare.
On gross appearance, schwannomas are usually solitary, well circumscribed, encapsulated tumours, which frequently undergo cystic degeneration. Histologically, typical schwannomas are composed of inter mixed Antoni A components (cellular and arranged in short bundles or interlacing fascicles) and Antoni B areas (less cellular and organized with more myxoid components). The cellular variant, which includes most large retroperitoneal and pelvic shwannomas, has a uniform spindle cell appearance without Antoni A or B areas. Characteristically, all Schwannomas show uniform and intense staining for S 100 protein (4).
The common pathological variants of schwannoma are :(a) Conventional schwannoma, which is a histologically benign tumour, which on occasions, causes destruction of surrounding osseous structures. (b) Ancient schwannoma, whih is a variant of schwannoma, displaying prominent degenerative changes like cyst formation, calcification, haemorrhage and hyalinization. These are large tumours which are usually deeply located (e.g. retroperitoneum). These tumours behave as ordinary schwannomas. (c) Cellular schwannoma, which is usually found in the deeper tissues (retroperitoneum or mediastinum). Histologically, it simulates malignant peripheral nerve sheath tumour (MPNST). There are compact spindle shaped cells arranged in a fascicular or whorled growth pattern. Verocay bodies and Antoni B areas are not conspicuous. Mitotic figures are present. The thick fibrous capsule around the tumour shows a dense lymphocyte infiltrate. Desmin is negative. (d) Plexiform schwannoma, which particularly in cellular form, and when occurring in childhood, simulates MPNST, and, (e) Melanotic schwannoma, which is a rare variant, and usually occurs in middle aged adults and commonly arises from the posterior spinal nerve roots. They are well circumscribed, partly encapsulated lesions, characterized by polygonal and vesicular cells with grooved nuclei. These cells contain abundant melanin pigment. Hence, it is often mistaken for melanoma. Less common variants are epitheloid schwannoma, glandular schwannoma, neuroblastomaâ€“like schwannoma and schwannoma-perineurioma(5),(6).
Schwannomas are often found incidentally, or present with vague, non specific symptoms. Schwannomas can rarely be almost entirely cystic, in which case they may resemble benign entities such as retroperitoneal pseudocyst, abscess or lymphocele. When Schwannomas are mostly solid, the differential diagnosis includes neurofibroma and lymphoma. The latter can be distinguished by the presence of separate lymphadenopathy (2). The retro peritoneum is non-restrictive, so that benign tumours are often able to grow to a large size by displacing adjacent structures before causing symptoms. They can occasionally cause bony changes in the spine, but otherwise do not invade or obstruct adjacent structures.
Malignant schwannomas are large in size and highly aggressive tumours. They are painful, and may cause many different symptoms depending on the location and size. They infiltrate into the adjacent structures and metastasize to distant sites. Histologically, the nuclear palisading may be a striking feature. There will be perineural and intraneural spread of tumour, lesional proliferation, or herniation into the lumina of the vessels. A combination of clinical, pathological and immunohistochemial studies help in the diagnosis of MPNST (7).
Nakashima et al (7), in an analysis of 25 cases of retroperitoneal tumours, found a significant correlation between irregular margins and malignancy. Other features that distinguish sarcomas from schwannomas, are invasion of local structures, distant metastases and brightly enhancing nodular areas of highly cellular tumuor. Well differentiated liposarcomas may also be characterized by the presence of fat. Hughes MJ et al (2), in their largest radiological series of abdominal or pelvic schwannomas, showed that a smooth well defined border, ovoid or spherical shape and location in the pre sacral region or lower retro peritoneum at the pelvic brim, are frequent findings in primary abdominal or pelvic schwannomas ; 11 of 13 cases showed all these features. Evidence of degeneration was common, with 8 schwannomas showing cystic change and 3 showing areas of calcification. The cystic schwannomas tended to be larger, with a mean diameter of 10.5 cm. Qiang Li et al (8), in an analysis of 82 cases of retroperitoneal schwannomas, found 81 cases (98.8%) of benign schwannoma and 1 case (1.2%) of malignant schwannoma. They concluded that most retroperitoneal schwannomas are benign. It is difficult to make an accurate pre operative diagnosis. However, with pre operative assessment of ultrasound guided fine needle aspiration, computed tomography, and magnetic resonance imaging, the accuracy of the diagnosis could be improved. The treatment depends solely on surgery. Malignant schwannomas are insensitive to chemotherapy and radiation, resulting in poor prognosis.
We report this patient with retroperitoneal / pelvic schwannoma because of its giant size, rare location, vague urinary symptoms and diagnostic dilemma.
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