Multimodal radiological imaging of collagenous fibroma arising from the subacromial region in a patient with osteosarcoma: A case report.

Collagenous fibroma arising from the subacromial region is extremely rare. It is important to distinguish collagenous fibroma from other fibrous tumors including desmoid tumors, to differentiate between the prognoses and management strategies, including surgical treatment. The present case report describes the case of a 42-year-old man with a collagenous fibroma of the subacromial region. He received a follow-up examination following treatment for osteosarcoma. Positron emission tomography (PET) scans used to assess for metastatic lesions indicated uptake in his left shoulder. The maximum standardized uptake value was 2.4. Magnetic resonance imaging demonstrated iso-intensity to muscle on T1-weighted images and iso-intensity with slightly high intensity on T2-weighted images. Post-contrast fat-suppressed magnetic resonance images indicated slightly heterogeneous enhancement of the lesion. There were no notable results from X-rays, bone scintigraphy and thallium-201 scintigraphy. Histological examination revealed collagenous fibroma. To the best of our knowledge, the present case is only the second incidence of collagenous fibroma arising from the subacromial region, and the first description of thallium-201 scintigraphy and PET scans in collagenous fibroma. The multimodal radiological data of this case may be useful for assisting in the differentiation of fibrous tumor types, including collagenous fibroma.