Case Report: Phosphaturic mesenchymal tumor arising from the jugular bulb without symptomatic osteomalacia

Phosphaturic mesenchymal tumor (PMT) is a rare mesenchymal neoplasm that may be associated with tumor-induced osteomalacia (TIO), typically through fibroblast growth factor 23 (FGF23)-mediated phosphate wasting. Skull-base PMTs are uncommon, and lesions centered on the jugular foramen or jugular bulb are particularly rare.

A 32-year-old man presented with progressive headache and dizziness for 2 months without bone pain, muscle weakness, or pathological fractures. Routine preoperative biochemical testing showed mild hypophosphatemia (0.78 mmol/L); this finding prompted further evaluation with a 24-h urinary phosphate measurement, which was elevated (48 mmol/24 h), together with mildly elevated alkaline phosphatase (147 U/L). Contrast-enhanced magnetic resonance imaging demonstrated a 2.4 × 2.5 × 2.0 cm enhancing mass in the left jugular foramen region. Preoperative CT showed a mixed-density lesion with multiple patchy calcifications, and bone-window CT demonstrated adjacent skull-base bone destruction involving the left jugular foramen and left hypoglossal canal. Magnetic resonance venography showed absent flow signals in the ipsilateral transverse sinus, sigmoid sinus, and internal jugular vein. The tumor was resected through a Fisch type A infratemporal fossa approach. Histopathological and immunohistochemical findings supported the diagnosis of PMT. The patient had no new postoperative neurological deficit or clinically apparent hearing deterioration. Without phosphate or vitamin D supplementation, serum phosphate, urinary phosphate, and alkaline phosphatase normalized after resection and remained within the reference range at 3 months.

PMT should be considered in the differential diagnosis of unusual jugular foramen masses, particularly when abnormalities of phosphate metabolism are present. This case illustrates that a jugular bulb PMT may be identified before symptomatic osteomalacia develops. In this patient, gross-total resection was followed by normalization of phosphate-related biochemical abnormalities and a favorable short-term clinical outcome.