Giant cell tumours of soft tissue are fibrohistiocytic neoplasms of uncertain behaviour that show morphological similarities to giant cell tumours of bone but are not related genetically.
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Terminology
Giant cell tumour of low malignant potential is a term that should not be used any longer 1.
Epidemiology
Giant cell tumours of soft tissue are very rare and seen in a wide range of ages with a peak incidence in the 5th decade. There is no predilection for gender or ethnicity 1,2.
Diagnosis
The diagnosis of giant cell tumours of soft tissue is established histologically, the location of the tumour is an important clue to diagnosis 1.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of soft tissue and bone tumours (5th edition) 1:
- multinodular tumour occurring in the superficial soft tissues
- a population of osteoclast-like giant cells and histiocytoid mononuclear cells
- frequent metaplastic bone formation and haemosiderin deposition
Clinical presentation
The tumours often present as indolent slowly-growing mass 1.
Pathology
Giant cell tumours of soft tissue are multinodular soft tissue neoplasms characterised by mononuclear histiocytoid cells and osteoclast-like giant cells frequently with metaplastic bone formation 1-3.
Aetiology
The aetiology of giant cell tumours of soft tissue is unknown 1.
Location
About 70% of the tumours affect the subcutaneous fatty tissue and the skin, and approximately 30% involve the deep soft tissues underneath the superficial fascia. Most giant cell tumours of soft tissue are located in the upper and lower limbs and a lesser number are situated in the trunk or the head and neck area 1.
Macroscopic appearance
Macroscopically giant cell tumours of soft tissue are solid well-demarcated nodular lesions with a brown-reddish to grey colour. Many tumours feature peripheral gritty regions of mineralised bone 1-3.
Microscopic appearance
The microscopic spectrum of giant cell tumours of soft tissue includes the following features 1-3:
- multinodular architecture with cellular nodules separated by sclerotic septa with sideritic components
- histiocytoid mononuclear cells with interposed multinucleated osteoclast-like giant cells
- stroma with abundant vascularity
- no nuclear pleomorphism
- rare necrosis
- osseous metaplasia in about half of the tumours
- commonly stromal haemorrhage and regressive change
Immunophenotype
Immunohistochemistry stains might express vimentin, CD68, smooth muscle actin or alkaline phosphatase. However, they do not seem to be particularly helpful 1.
Genetics
Different to giant cell tumours of bone mutations of the H3-3A (H3F3A) gene are typically absent 1,2.
Radiographic features
There are only a few reports where imaging features of giant cell tumours of soft tissue have been described, they include the following 3,4:
- cystic lesions with internal nodules or debris
- possible daughter cysts
- adjacent nondescript soft tissue changes
Ultrasound
Ultrasound appearances have been described as cystic with an internal hyperechoic solid nodule possibly associated with daughter cysts and internal debris 3,4.
MRI
Cystic lesions with fluid-fluid levels and differences in signal intensity as well as internal or adjacent solid portions or nodules have been reported as imaging features. Cyst wall and solid portions of the tumours have been described with the following signal characteristics 3,4:
- T1: low to intermediate signal intensity
- T2: low to intermediate signal intensity
- T2FS/STIR: high signal
- T1 C+ (Gd): avid enhancement of cyst wall and solid portions
Radiology report
The radiological report should include a description of the following points:
- form, location and size
- tumour margins
- relation to the muscular fascia
- relationship to bones, tendons and joints
- relationship to local nerves and vessels
Treatment and prognosis
The common management is surgical excision. Local recurrence is uncommon and occurs in about 12%. Metastases are very rare 1.
History and etymology
Giant cell tumour of soft tissue was first reported in 1972 by the British pathologist R Salm and orthopaedic surgeon HA Sissons 3,5.
Differential diagnosis
The differential diagnosis of giant cell tumours of soft tissue are the following 3,4:
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