Definition
A variant of fibrous histiocytoma located in subcutaneous or deep visceral soft tissues.
The tumour occurs across a wide age range, rarely in children.
Most subcutaneous tumours occur on the extremities. Those in deep soft tissues occur in the mediastinum, retroperitoneum and pelvis.
Subcutaneous tumours average 2.5 cm. Those in viscera average 9 cm. The tumour is well demarcated, often with a fibrous pseudocapsule. It is firm with a yellow-tan cut surface. There may be cystic degeneration.
A storiform is always present and often dominates. Cells are ovoid or spindled with pale cytoplasm and bland nuclei containing single small nucleoli. The mitotic rate is variable and may be high. There is always a lymphocytic infiltrate: at the periphery, this may be so dense as to mimic a lymph node. There may be Touton giant cells or foam cells. Blood vessels may have a staghorn configuration. The stroma may be focally hyalinised. Rarely, there is metaplastic ossification.
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Solitary fibrous tumour: lacks a storiform pattern but has alternating hypocellular and hypercellular areas. May also be positive for CD341.
DFSP: has a dermal origin with infiltrative extension into subcutis. Nuclei are small and slender. A lymphocytic infiltrate is usually absent.
Low grade sarcoma
Soft tissue perineuroma; there is a whorled architecture. Cells have bipolar processes and very thin nuclei. EMA is positive, highlighting the cell processes.
Giant cell tumour of tendon sheath: usually in the digits: lacks a storiform pattern.
Giant cell tumour of soft tissue: is multinodular and lacks a storiform pattern: metaplastic bone is common.
Recurrence is common after incomplete excision. Rarely, metastasis occurs.
©SMUHT/PW Bishop