Cranial and extracranial fasciitis of childhood: a clinicopathologic and immunohistochemical study.

Fasciitis of various types constitutes a distinctive category of soft tissue lesions whose microscopic features are known for their potential to evoke a pathological diagnosis of one or another type of sarcoma. Nodular fasciitis is the archetype of this group of "fibrous tumors." Cranial fasciitis is considered a nonneoplastic lesion similar to nodular fasciitis, which is seen almost exclusively in infants and children and has unique clinicopathologic features. The current study documents our experience with fibrous-myofibroblastic proliferations in extracranial sites, mainly in the head and neck region of young children, whose histological features resemble those of cranial fasciitis. These lesions were composed of loosely arranged spindle to stellate cells in a myxoid background. One patient in the study had both cranial and extracranial involvement. Some histological overlap between nodular fasciitis and cranial-extracranial fasciitis was noted, but the latter lesion tended to be more uniform in appearance than nodular fasciitis with its fascicular, spindle cell features and variability in histological patterns within the same lesion, unlike the more consistently uniform myxoid appearance of the cranial and extracranial lesions. Immunohistochemically, the spindle cells of the extracranial lesions and the one case of cranial fasciitis co-expressed vimentin and smooth muscle actin. The extracranial lesions had a predilection for children in the first year of life with all cases occurring at or before 2 years of age, unlike nodular fasciitis, which is rarely seen in the first 4 to 5 years of life. The cranial and extracranial fasciitides should be differentiated from the fibromatoses that tend to locally recur, unlike the nonrecurring behavior of these lesions in common with the other types of fasciitis.