[Solitary dorsal paravertebral tumor: radiological and histopathological characterization of a pediatric case of nodular fasciitis].

Nodular fasciitis is a benign soft tissue lesion with rapid fibroblastic or myofibroblastic proliferation, rarely observed in pediatric patients. Here, we present the case of a seven-year-old boy with no relevant medical records, in whom an asymptomatic dorsal tumor was incidentally identified. Magnetic resonance imaging showed a left dorsal paravertebral lesion with hypointensity on T1, hyperintensity on T2, peripheral contrast enhancement, and the so-called fascial tail sign. Complete surgical resection of the lesion was achieved. The histopathological study showed a proliferation of spindle or stellate cells with nuclei without atypia in a myxoid or collagenized stroma. The immunohistochemical profile showed positivity for smooth muscle actin, muscle-specific actin antibody HHF35, and calponin. The lesion was diagnosed as nodular fasciitis, an entity with broad and complex differential diagnosis. Presence of specific radiological signs and adequate immunohistochemical characterization of the lesion help perform an accurate diagnosis.