Phosphaturic mesenchymal tumor: Case report

Abstract

Phosphaturic mesenchymal tumors (PMT) are an extremely rare pathologic phenomenon that presents as paraneoplastic tumor-induced osteomalacia. Their diagnosis is often significantly delayed due to their rare occurrence in addition to the generalized and vague symptoms of their presentation including progressive bone pain, myopathies, arthralgias, fractures, and generalized weakness. This case report identifies a very characteristic presentation of a 37-year old African American male suffering from a PMT; with symptom onset presenting over 5-years prior to presentation with a consistent complaint of progressive and debilitating quadriparesis. The tumor was first identified by pelvic computerized tomography, although it was initially thought to be a noncontributory benign soft tissue mass. It was only after being hospitalized due to a severe and unresponsive hypophosphatemic state (less than 1 mg/dl) that the collective differential switched to one of a PMT with follow up nuclear 99mTc bone scintigraphy and magnetic resonance imaging being used to aid in the overall assessment of changes, extent, and general metabolic properties of the tumor. The confirmatory diagnosis of a PMT was later established through both serum fibroblast growth factor 23 testing and histopathologic review of the surgically removed specimen. By including this rare but curative disease into the differential of osteomalacia and thereby further examining patient serum phosphate levels, the previous 5-7 year delay in diagnosis will be dramatically reduced.

Keywords: Phosphaturic mesenchymal tumor.

Fig. 1

Pelvic CT without contrast. The mass is identified just lateral to the patient's left greater trochanter with a density of 19.3 Hounsfield unit (HU), connecting the tumor to a soft tissue pathology.

Fig. 2

Pelvic CT without contrast. The mass was measured at 58.5 × 38.9 mm.

Fig. 3

Whole-body nuclear 99mTc bone scintigraphy. (Arrows) Demonstrates the mass with slight uptake found in the left hip. The skeletal absorption demonstrates a pattern consistent with metabolic bone disease.

Fig. 4

T1 weighted MRI without contrast. (Arrow) Presenting the encapsulated mass of 8.5 × 7.4 × 6.5 cm with heterogenous isointensity in comparison to the surrounding pelvic musculature.

Fig. 5

T2 weighted MRI without contrast. (Arrow) Displaying heterogenous hyperintensity in comparison to the surrounding pelvic musculature.

Fig. 6

Contrast T1 weighted MRI. (Arrow) Showing heterogeneous contrast enhancement throughout with heavy vascularity visualized on the encapsulated periphery.

Fig. 7

Histologic image of phosphaturic mesenchymal tumor. Illustrating hemangiopericytoma-like areas.

Fig. 8

Histologic image of phosphaturic mesenchymal tumor. Displaying osteoclastic giant cells.