Pathology of Myofibroblastic Tumours
7. Inflammatory myofibroblastic tumour
8. Low-grade myofibroblastic sarcoma
9. High grade myofibroblastic sarcoma
Inflammatory Myofibroblastic Tumour:
Inflammatory myofibroblastic tumour (inflammatory fibrosarcoma) represents a spectrum of myofibroblastic proliferations.
Meis et al. proposed that some of the intra-abdominal tumours which were previously designated as inflammatory pseudotumour or inflammatory myofibroblastic tumours where actually sarcomas.
However Coffin et al. suggested that these were benign myofibroblastic proliferations.
This tumour has potential for recurrence and persistent local growth.
It may progress to frank sarcomatous tumour and metastases have been recorded.
Hence, inflammatory myofibroblastic tumour is best regarded as a low grade sarcoma.
This tumour is frequently seen in children and adolescents, in the intra-abdominal and retroperitoneal sites.
The tumour presents as a solid well circumscribed or a multinodular mass.
Three main histologic patterns:
1. Nodular fasciitis-like
2. Fibrous histiocytoma-like
3. Desmoid or scar tissue-type The tumour displays an admixture of myofibroblasts and fibroblasts arranged in short interwoven fascicles set in a collagenous stroma.
Occasionally, larger polygonal cells or ganglion-like cells may be present.
A polymorphic inflammatory cell component composed of lymphocytes and plasma cells are identified in the backround.
The backround stroma may demonstrate three histologic patterns:
(i) Hypocellular fibrous
The tumour cells express vimentin, muscle specific actin and alpha-smooth muscle actin.
Focally, the tumour cells are desmin and cytokeratin positive.
Cytogenetic analysis reveals clonal aberrations usually involving 2p.
There is fusion of the ALK gene with TPM4 and TPM3 (tropomyosin) genes have been reported and there is immunohistochemical expression of ALK.
Low Grade Myofibroblastic Sarcoma:
These lesions are usually seen in adults.
However, similar cases have been reported in children.
Commonly located in the deep soft tissue of the oral cavity (tongue), the extremities, the trunk and the abdominal / pelvic cavities.
Microscopically, these are diffusely infiltrative tumour composed of cellular fascicles of spindle-shaped tumour cells displaying myofibroblastic cytological features.
Some cases are hypocellular with a prominent collagenous matrix.
The tumour cells display mild to moderate nuclear atypia wih enlarged hyperchromatic nuclei.
Immunohistochemistry reveals variable actin and desmin positivity ( actin +/ desmin - , actin - / desmin +, or actin + / desmin +)
Most cases stain positively for fibronectin.
Some cases are CD34 and CD99 positive.
S100 protein and epithelial markers are negative.
Differential diagnosis includes benign and malignant spindle cell tumours
High Grade Myofibroblastic Sarcoma:
High grade (MFH -like) myofibroblastic sarcoma have been reported in children and adults.
In children these are usually located in the head and neck region.
In adults these are common in the extremities.
Salient histological features:
Spindle shaped cells arranged in herringbone or fascicular patterns.
There is abundant collagen production.
Pleomorphic MFH-like areas are present.
Numerous mitotic figures are present.
There are areas of tumour necrosis.
Electron microscopic examination confirms myofibroblastic line of differentiation.
Histologically it is often extremely difficult to distinguish between myofibroblastic and smooth muscle tumours. Myogenic tumours
Rhabdomyosarcoma (myoglobin, MyoD1,myf-4 are negative in myofibroblastic sarcoma)
Malignant peripheral nerve sheath tumour excluded by electron microscopy and immunohistochemistry
Inflammatory myofibroblastic tumour of paranasal sinuses with fatal outcome: reactive lesion or tumour?
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