Increased Tc-99m MDP Activities in Multifocal Atypical Ossifying Fibromyxoid Tumor

A 63-year-old male patient presented with a 10-year history of a gradually enlarging, painless mass on his back, which was initially noticed without any signs of redness, swelling, or tenderness. Physical examination revealed multiple hard, nontender subcutaneous nodules without signs of inflammation or pigmentation. Computed tomography (CT) of the back revealed the presence of multiple internal calcifications within the mass [Figure 1a, arrow]. Whole-body bone scintigraphy (WBS) with Tc-99 m MDP was subsequently performed to evaluate the relationship between the dorsal mass and osseous structures, as well as to determine the extent of involvement. The scintigraphy results revealed multiple areas of abnormally hyperactive uptake in subcutaneous regions [Figure 1b, arrow], suggesting extraosseous uptake. Pathological examination of the back mass confirmed an atypical ossifying fibromyxoid tumor (OFMT), characterized histologically by cord-like nests of uniform round cells within a fibromyxoid stroma showing peripheral ossification [Figure 1c]. Immunohistochemical studies revealed EMA (+), S100 (-), Desmin (+), SMA (-), CD34 (-), Ki67 (LI: 5%).

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Figure 1 Axial computed tomography of the back revealed calcified mass (a, arrow). Anterior and posterior views of whole-body bone scan showing multifocal subcutaneous radiotracer accumulation (b, arrow). Pathological examination of the back mass confirmed an atypical ossifying fibromyxoid tumor, characterized histologically by cord-like nests of uniform round cells within a fibromyxoid stroma showing peripheral ossification (c).

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OFMT is a rare soft-tissue neoplasm that most commonly occurs in the subcutaneous tissues of the trunk or extremities with occasional cases involving the head and neck, typically characterized by a slow-growing, solitary mass with a fibrous and myxoid matrix and peripheral ossification.[123] Multifocal presentation is exceedingly rare, and the imaging characteristics, particularly on bone scintigraphy, are not well-documented in the literature. Compared to CT, WBS demonstrates distinct advantages in evaluating multifocal calcified lesions, particularly in metabolic activity detection, whole-body assessment, differentiation of etiology, and guidance for biopsy.[456] This is critical for identifying occult metastatic lesions. In contrast, CT requires region-specific protocols, increasing both radiation exposure and workflow complexity. Therefore, the authors propose that WBS should be considered a first-line screening modality for systemic evaluation of multifocal OFMT. This case highlights an unusual presentation of multifocal subcutaneous atypical OFMT with unique imaging findings, emphasizing the importance of considering OFMT in the differential diagnosis of multifocal subcutaneous calcified masses. Clinicians should be aware of the potential for extraosseous Tc-99 m MDP uptake in such cases and consider OFMT as a possible diagnosis.[789] Early and accurate diagnosis is crucial for guiding appropriate management and improving patient outcomes.[210]