A pediatric case of a phosphaturic mesenchymal tumor: A “nonphosphaturic” variant in the infratemporal skull base

Abstract

Objectives: To describe a rare case of infratemporal phosphaturic mesenchymal tumor (PMT), a “nonphosphaturic” variant in the infratemporal skull base, in a 5-year-old boy. Methods: This was a retrospective study of the patient's clinical and biochemical features, computed tomography (CT), maxillofacial magnetic resonance imaging (MRI), histopathology as well as surgical treatment and follow-up. Results: The boy suffered from a right preauricular mass and ipsilateral hearing loss. Temporal bone CT and maxillofacial MRI demonstrated a circumscribed infratemporal skull base lesion. Histomorphologically, the lesion demonstrated typical microscopic features of PMTs and was positive for vimentin, smooth muscle actin, and FGF-23. However, there was no clinical or biochemical evidence of tumor-induced osteomalacia (TIO), and ultimately a diagnosis of a “nonphosphaturic” variant of PMTs was made. No postoperative recurrence was observed during follow-up. Conclusions: PMTs are rare and have a low incidence among children. They are histologically distinctive tumors associated with phosphaturia and TIO. So-called “nonphosphaturic” variants, occurring without known phosphaturia, are even rarer. Pathologists and clinicians need to be aware of the presence of a PMT with an absence of osteomalacia symptoms. Wide surgical resection and long-term follow-up are necessary. Intraoperative functional and aesthetic concerns should be emphasized as well, particularly in pediatric patients.

Keywords

• Phosphaturic mesenchymal tumor (PMT)
• “Nonphosphaturic” variant
• Fibroblast growth factor 23 (FGF-23)
• Oncogenic osteomalacia
• Infratemporal skull base