Phosphaturic Mesenchymal Tumors from Head to Toe: Imaging Findings and Role of the Radiologist in Diagnosing Tumor-Induced Osteomalacia

Phosphaturic mesenchymal tumor: two cases highlighting differences in clinical and radiologic presentation

Phosphaturic mesenchymal tumors are rare, usually benign neoplasms that occur in the soft tissue or bone and are the cause of nearly all cases of tumor-induced osteomalacia. Tumor-induced osteomalacia due to phosphaturic mesenchymal tumor is a challenging diagnosis to make-patients present with variable clinical and radiologic findings and the culprit neoplasm is often small and can occur anywhere head to toe. We present two cases of phosphaturic mesenchymal tumor in the scapular body and plantar foot. In both cases, the patient endured years of debilitating symptoms before a tissue diagnosis was eventually reached. Descriptions of clinical presentation, laboratory workup, surgical resection, and imaging characteristics, with a focus on CT, MRI, and functional imaging, are provided to assist with the diagnosis and management of this rare entity. A brief review of current literature and discussion of the differential diagnoses of phosphaturic mesenchymal tumor is also provided.

Phosphaturic Mesenchymal Tumor Along the Hallux side Inducing a Chronic non-Healing Wound: A Case Report with Literature Review

Phosphaturic mesenchymal tumor (PMT) is a rare paraneoplastic syndrome characterized by renal phosphate wasting, hypophosphatemia, and bone calcification disorders. Complete surgical resection of the tumor is believed to be the most effective treatment measure. However, the diagnosis of PMT is very difficult because of its insidious and small size, especially, when it appears in subcutaneous tissue with a chronic non-healing wound. We report a rare case of a 38-year-old man with a chronic non-healing wound on the left hallux for approximately eight months. Plain radiographic images and magnetic resonance imaging (MRI) revealed a cystic radiolucent shadow in the left distal phalanx. Bone scan observations also showed increased uptake in the same location. Histologically, this tumor was composed of numerous spindle cells with clusters of giant cells. The serum FGF23 level was significantly higher before surgery, with higher FGF23 levels closer to the tumor. Reverse transcription polymerase chain reaction and immunohistochemistry further confirmed the high expression of FGF23 in tumors. These data suggest that FGF23 may be a potential causative factor of PMT. The serum FGF23 levels might be useful for the diagnosis of PMT and localization of the tumor. The tumor was CD56- and D2 to 40-positive and CD31-negative. The non-healing wound caused by PMT might be attributed to the invasive growth of the tumor, destruction of intercellular junctions, and decrease in the number of endothelial cells.

Imaging characteristics of phosphaturic mesenchymal tumors

BACKGROUND

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome associated with phosphaturic mesenchymal tumors (PMTs). Localization of the causative tumor in these cases is an arduous task since the culprit lesions are usually small, slow-growing, and can be located almost anywhere from head to toe.

PURPOSE

To describe the morphological characteristics of histologically proven PMTs on various radiological modalities.

MATERIAL AND METHODS

After institutional ethical approval, this retrospective study analyzed 20 cases with a histopathological evidence of PMT. Various imaging characteristics of the tumors on available computed tomography (CT) and magnetic resonance imaging (MRI) scans were evaluated. Descriptive statistical analyses were conducted.

RESULTS

The tumors were located in diverse locations: lower extremities (n = 10); head and neck (n = 5); vertebral column (n = 3); pelvis (n = 1); and upper extremities (n = 1). Bone lesions seen on CT had variable morphology: sclerotic (n = 3/8, 37.5%); lytic (n = 3/8, 37.5%), and both lytic and sclerotic (n = 2/8, 25%) with presence of narrow zone of transition in all cases (n = 8/8) and amorphous internal matrix calcifications in 25% of cases (n = 2/8). Of the tumors, 68.4% (n = 13/19) were hypointense on T1 and all of them showed hyperintense signal on T2-weighted and STIR images (n = 19/19) and contrast enhancement (n = 16/16). Of the tumors, 66.7% (n = 6/9) showed restricted diffusion. DOTANOC PET/CT showed tumor uptake in all cases (n = 8/8).

CONCLUSION

PMTs may have variable and non-specific tumor appearances on various imaging modalities. However, in an appropriate clinical scenario and a background of suggestive biochemical work-up, the radiologist should keep a high index of suspicion.

Tumor-induced osteomalacia characterized by "painful knee joint with difficulty in moving": a case report

BACKGROUND

Tumor-related osteomalacia (TIO) is a rare paraneoplastic syndrome characterized by severe hypophosphatemia and osteomalacia. The diagnosis of TIO can be very difficult because of its nonspecific nature of clinical manifestations. Here we reported a case of young TIO patient with "painful knee joint with difficulty in moving" to improve the clinical diagnosis and treatment levels.

CASE PRESENTATION

The patient's clinical features were consistent with TIO. A tumor was successfully located in left tibial by ⁶⁸Ga-DOTATATE PET/CT, and then was surgically resected. Upon pathologic assessment, the tumor was diagnosed as phosphaturia stromal tumor (PMT) with positive Vim staining. After the surgery, serum phosphate level rapidly recovered and symptoms significantly improved.

CONCLUSION

TIO should be considered in patients with chronically hypophosphorus osteomalacia in the setting of no family history. Early removal of the responsible tumors is clinically essential for the treatment, and imaging examination is of great significance for tumor localization.

Phosphaturic Mesenchymal Tumor

Phosphaturic mesenchymal tumors (PMTs) are neoplasms associated with tumor-induced osteomalacia. Patients typically present with pathologic fractures in the setting of chronic hypophosphatemic hyperphosphaturic osteomalacia, as well as gradual muscle weakness, bone pain, and difficulty walking. Because of their rarity and nonspecific symptomatology, phosphaturic mesenchymal tumors often go undiagnosed for years. Even when discovered on imaging, the tumors can be diagnostically challenging for radiologists. Phosphaturic mesenchymal tumors often tend to be small and can be located nearly anywhere in the body, and, therefore, can mimic many other tumors. This case highlights the imaging and pathologic markers of a phosphaturic mesenchymal tumor, often found in a patient with tumor-induced osteomalacia.

Phosphaturic mesenchymal tumors: radiological aspects and suggested imaging pathway

Phosphaturic mesenchymal tumors (PMTs) are rare mesenchymal neoplasms of soft tissue or bone origin that can give rise to a challenge in diagnostic imaging. These tumors are frequently associated with tumor-induced osteomalacia, also called oncogenic osteomalacia, which is a rare paraneoplastic syndrome characterized by ectopic secretion of fibroblast growth factor 23, a hormone that regulates serum phosphate level. PMTs show polymorphic features on both radiological findings and histological examination, causing problems in diagnosis owing to their similarity with other mesenchymal tumors. Thus, this paper aims to describe radiological aspects of PMTs and suggest an imaging pathway for accurate diagnosis throughout the evidence from the literature review.