Aggressive juvenile mandibular fibromatosis

Abstract

Aggressive juvenile fi bromatosis of the jawbones is a rare tumor presenting as infi ltrative mass with unpredictable evolution. We report herein a 17-year-old student with a 6-month history of radiologically proven resorption of a part of the mandible, lingual displacement of tooth 34 and malocclusion. Alveolar ridge resorption and three dark-brown foci in the bone were seen after the tooth was extracted. Histological study showed the tumor tissue to have a bundle-like structure; immunohistochemically it was positive for vimentin, smooth muscle actin, β-catenin, Ki-67 (5%), and negative for desmin and cytokeratin 34bE12. The golden standard in the diagnostics of desmoid fi bromatoses is the nuclear or membrane expression of β-catenin, which is found in 90% of the cases. Differential diagnosis include mandibular fi broma, well-differentiated fi brosarcoma, fi brosing histiocytoma, and infi ltration from adjacent soft-tissue tumor. Aggressive juvenile fi bromatosis should be managed by radical excision. Local recurrences are not rare, but metastases do not develop. In rare cases this type of fi bromatosis has been known to regress spontaneously. Aggressive fi bromatosis is a diagnostic challenge, since it remains in the grey zone between benign and malignant lesions of the oral cavity.