Retroperitoneal leiomyoma (versus leiomyosarcoma)

Epidemiology

Retroperitoneal leiomyomatous tumours are rare, accounting for only 0.5-1.2% of retroperitoneal tumours. Most retroperitoneal smooth muscle tumours have been considered to be malignant, with little published evidence of the criteria for benignity. Retroperitoneal and intra-abdominal leiomyomas occur almost exclusively in adult women.

Histopathology

• retroperitoneal leiomyomas resemble uterine leiomyomas, with a whorled cut surface. They should have three or less mitoses per 50 HPF and should be devoid of coagulative necrosis and atypia.

• further studies are needed of tumours in the range of 4 to 10 mitoses / 50 HPF.

Immunohistochemistry

Differential diagnosis

• Parasitic uterine leiomyomas.

• Cases of retroperitoneal leiomyomas with copious fat: myolipoma

• Leiomyosarcoma: occur sin older women, have greater cellularity, mitotic activity and necrosis. They are not usually strongly positive for oestrogen receptor.

• GIST; these tumours are more cellular than leiomyomas, may have an epithelioid morphology and are positive for CD117, usually positive for CD34, variably positive for SMA and rarely positive for desmin.

• Schwannoma; positive for S-100 and negative for SMA

• Solitary fibrous tumour; positive for CD34 and almost always negative for SMA and desmin.

• Angiomyolipoma: positive for HMB-45, Melan-A and microphthalmia transcription factor.

References

1Paal, E., Miettinen, M. Retroperitoneal leiomyomas: a clinicopathologic and immunohistochemical study of 56 cases with a comparison to retroperitoneal leiomyosarcomas. Am J Surg Pathol 2001;25:1355-1363.

2Billings, S. D., A. L. Folpe, et al. (2001). "Do leiomyomas of deep soft tissue exist? An analysis of highly differentiated smooth muscle tumors of deep soft tissue supporting two distinct subtypes." Am J Surg Pathol 25(9): 1134-42.

This page last revised 30.6.2004.

©SMUHT/PW Bishop