Teaching Case

Nulligravida with a nontender right pelvic mass incidentally discovered. Preoperative abdominal and transvaginal US showed a solid lesion posterior to the uterus, adjacent to the right ovary.

A routine gynaecological examination in an asymptomatic nulligravid woman revealed a nontender right pelvic mass. Abdominal and transvaginal US showed a solid lesion, posterior to the uterus, adjacent to the right ovary. At laparotomy the mass, which occupied the presacral region, was resected. The pathological diagnosis was schwannoma.

Schwannomas (neurilemomas or neurinomas) are benign peripheral nerve sheet tumours that may develop nearly anywhere in the body, especially in the head, neck and extremities. Although 11% of schwannomas occur in the retroperitoneum, the pelvic retroperitoneum represents a very rare location. Retroperitoneal schwannomas occur mainly in young to middle aged adults as solitary slow-growing masses. As the symptoms appear late, these tumours may reach considerably large dimensions and usually present degenerative changes such as cyst formation and haemorrhage. Cystic changes have been highlighted as a common feature of retroperitoneal schwannomas. However, in the presented case, presumably because the tumour was smaller, US showed a solid lesion with a minimal cystic component.

The ultrasonic differential diagnosis in this case included haemorrhagic ovarian cyst, uterine leiomyoma, endometrioma and a para-ovarian complex cyst. Correlation to other imaging techniques, namely CT and MR, could have helped in the diagnosis.

The treatment of choice for schwannomas is enucleation. When resection is incomplete, which it was not this case, recurrences may occur but malignant transformation is extremely rare. Although most schwannomas are sporadic, some occur in the setting of neurofibromatosis type 2. To exclude this disease, the patient in this case underwent a complete neurological examination and MRI of the neuroaxis, both of which were normal.