Clear cell myomelanocytic tumour of the falciform ligament / ligamentum teres

Definition

This is a member of the family of PEComas, co-expressing melanocytic and muscle markers, occurring in or immediately adjacent to the falciform ligament of ligamentum teres.

Epidemiology

This is a tumour of children and young adults with a strong female predominance.

Clinical features

Patients present with pain and/or an abdominal mass.

Macroscopic appearances

One case occurred in the omentum adjacent to the falciform ligament. A similar tumour has been reported occurring the thigh². Tumours are firm, tan grey and show haemorrhage and cystic change.

Histopathology

The tumour is composed of spindle cells with clear to pale eosinophilic cytoplasm. The cells are arranged in fascicles and nests. They have small distinct nucleoli. The mitotic count is low, less than 1/20 HPF. There is an elaborate vasculature, resembling that seen in renal cell carcinomas. Necrosis is not seen.

Immunohistochemistry

	HMB-45	7/71, 1/1 (tumour of thigh)2
	S-100	0/71, 0/1 (tumour of thigh)2
	SMA	3/31, 1/1 (tumour of thigh)2
	Melan-A	3/31, 0/1 (tumour of thigh)2
	MITF	3/31, 1/1 (tumour of thigh: focal positivity)2
	Myosin	3/31
	Desmin	0/31, 0/1 (tumour of thigh)2
	TSC2	0/31
	Vimentin	1/1 (tumour of thigh)2
	Cytokeratin	0/1 (tumour of thigh)2

Ultrastructure

The spindle cells contain abundant glycogen. There are numerous melanosomes; sometimes a small amount of melanin is present. Hemidesmosomes and primitive cellular junctions are common.

Differential diagnosis

• Clear cell sarcoma of tendons and aponeuroses: there is an admixture of spindle and epithelioid areas, with tumour giant cells. Nucleoli are relatively large. There is positivity for S-100 and melanocytic markers but negativity for SMA and myosin. A t(12;22) translocation is characteristic.

• Leiomyosarcoma: patients are much older. Fascicles are shorter and intersect at right angles. The tumour cells have more eosinophilic cytoplasm. Nuclei are cigar-shaped. There is negativity for melanocytic markers but usually positivity for desmin.

• Clear cell smooth muscle tumour of childhood

• Monotypic angiomyolipoma: is composed of epithelioid cells and lacks a nested pattern. Malignant angiomyolipoma shows frankly sarcomatous features.

Prognosis

These are potentially malignant tumors with a capacity to metastasize.

References

¹Folpe, A. L., Z. D. Goodman, et al. (2000). "Clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres: a novel member of the perivascular epithelioid clear cell family of tumors with a predilection for children and young adults." Am J Surg Pathol 24(9): 1239-46.

²Folpe, A. L., J. K. McKenney, et al. (2002). "Clear cell myomelanocytic tumor of the thigh: report of a unique case." Am J Surg Pathol 26(6): 809-12.

This page last revised 6.1.2005.

©SMUHT/PW Bishop