Unmasking Skull Base Phosphaturic Mesenchymal Tumors: A Rare and Treatable Cause of Tumor-Induced Osteomalacia.

Tumor-induced osteomalacia (TIO) is a rare syndrome caused by phosphaturic mesenchymal tumors that secrete substances, like FGF23, leading to phosphorus loss and osteomalacia. These tumors are often small and challenging to locate. Surgical excision is the primary treatment and usually results in symptomatic improvement. This report presents seven cases of skull base origin of these tumors to add to the existing literature. This retrospective study reviewed patients with phosphaturic mesenchymal tumors (PMT) who underwent surgical excision at a tertiary care institute from 2015 to 2023, focusing solely on tumors confined to the anterior or lateral skull base. The analysis included demographics, clinical features, biochemical and radiologic findings, tumor location, surgical details, and follow-up. The study included 7 patients (6 males, 1 female) with ages ranging from 40 to 65 years (mean age: 52 years). Common symptoms included lower back pain (70%), fractures (42%), difficulty walking (42%), and muscle weakness (28%). All patients showed hypophosphatemia, and elevated FGF23 levels were noted in 5 out of 7 patients (70%). Most tumors (86%) were in the anterior skull base, particularly in the ethmoid region. One patient had a tumor in the lateral skull base, confined to the mastoid. All patients underwent wide local excision via endoscopic and retromastoid approaches. Phosphaturic mesenchymal tumor-induced osteomalacia is a rare condition, with generalized nonspecific symptoms. Despite the challenging nature of the disease, surgical removal of the tumor can lead to a complete cure and significant symptom relief.