Myofibroma

Myofibromatosis is an admixture of myofibroblasts and fibroblasts within a fibrous stroma. It is usually less aggressive than pure fibromatosis of the oral region, but it may be part of a congenital generalized fibromatosis or generalized hamartomatosis.  Multiple lesions tend to fall into two categories: superficial myofibromatosis, with nodules confined to subcutaneous and submucosal stroma, with occasional involvement of skeletal muscle or bone; and generalized myofibromatosis, with visceral lesions and a mortality rate approaching 80%. Some authorities prefer to use the term myofibroma for single lesions, especially those with adult onset, and myofibromatosis for multifocal involvement. This is considered to be a developmental anomaly but some lesions occur in adults. Many cases have a close clinical and microscopic similarity to fibromatosis, hence, its inclusion in this section of the present chapter.

Myofibromatosis presents in the paraoral region as a single or as multiple submucosal nodules, usually in neonates and infants.

Myofibromatosis or myofibroma presents with a microscopic appearance similar to that of fibromatosis but the peripheral cells demonstrate eosinophilic cytoplasm reminiscent of smooth muscle. There is usually a biphasic pattern of lightly staining fibrous areas separated by regions of pericyte-like vascular cell or smooth muscle-like spindle cell proliferations. The lesion is most vascular centrally, where it may mimic a hemangiopericytoma or glomus tumor, with lesional cells proliferating around blood vessels. Collagen is present but seldom abundant. The more fibrotic lesions, of course, must be differentiated from fibromatosis, irritation fibroma, neurofibroma, angiofibroma, and fibrotic pyogenic granuloma, according to criteria described for those lesions.

Lesional cells show features of both myofibroblastic and fibroblastic cells, with fuchsinophilic and PTAH-positive intracellular fibrils. These cells are immunoreactive for vimentin and actin, but not for desmin or S-100 protein.  These stains help to demonstrate the smooth muscle nature of the lesion and to separate myofibromatosis from neurofibroma and fibrous histiocytoma, although they are less helpful for nodular fasciitis, which also contains myofibroblasts.

Myofibromatosis is much more innocuous than fibromatosis and spontaneous regression may occur, although multifocal involvement may produce serious extragnathic difficulties for the patient. The typical treatment for oral lesions is conservative surgical removal, with minimal recurrence expected.

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