A Case of Tumor-Induced Osteomalacia: Finding the Culprit Acetabular Tumor and Successful Resection with a Novel Hip Joint-Preserving Surgery

Abstract

Introduction: Tumor-induced osteomalacia (TIO) is a rare paraneoplastic disorder caused by tumors that produce fibroblast growth factor 23 (FGF23) resulting in phosphate wasting and inadequate bone mineralization. Complete resection of the tumor can be curative. However, these tumors are typically difficult to find anatomically due to small size and location.

Case report: We present the case of a patient who presented for evaluation of recurrent fractures and hypophosphatemia in the setting of elevated FGF23 suggestive of TIO. 68Gallium-DOTATATE revealed multiple somatostatin avid lesions in several ribs, left acetabulum, sacrum, right tibia, and feet, some of which appeared with fracture on computed tomography scan, initially concerning for metastatic disease. However, the lesion in acetabulum was considered the culprit tumor given its remarkably higher maximum standard uptake values. Complete surgical removal of the FGF23-secreting tumor led to cure of this disease.

Conclusion: This case report highlights the challenges with functional imaging differentiating fractures from the culprit lesion and reports on a novel surgical technique that allowed for surgical cure while preserving the hip joint.

Keywords: Hypophosphatemia; functional imaging; osteomalacia; surgical technique; tumor.

Figure 1

68Gallium - DOTATATE positron emission tomography/computed tomography (PET/CT). Abnormal uptake in multiple fractures of ribs, right tibia, ankles, and feet (a). PET and CT scan showed abnormal uptake (SUVmax 20.4) in left posterior acetabulum in red circle (b and c).

Figure 2

3D-Printed Cutting Guide (CG). Model shows planned bone cuts [red] and tumor [green] (A). CG pinned on bone (B). Bone defect model after tumor removal (C). Bone defect models (D). Printed CG (E). CG fitting model (F). CG fitting cut defect (G).

Figure 3

Left acetabulum pathology images. Tumor measures 1.4 cm (red circle) (a), closest margin to hip joint inked blue (b). Phosphaturic mesenchymal tumor with hemorrhagic areas (c), islands of entrapped trabecular bone (d), and sheets of bland spindle cells (e) H and E, original magnification ×2.5 (c), ×20 (d), ×40 (e).

Figure 4

Post-operative imaging. (a and b) X-rays of reconstruction showing tantalum augment filling the void and stabilized with additional posterior column plate. (c) Sagittal post-operative computed tomography scan showing hip joint-sparing reconstruction.