Inflammatory mass or malignancy? The radiology of fish bone phlegmon: a review of 3 cases

Soft-tissue sarcomas of the abdomen and abdominal wall are rare, and their imaging appearances can overlap with those of benign inflammatory conditions. Foreign body-related phlegmon caused by a migrated fish bone from the bowel represents an uncommon but important diagnostic mimic, often indistinguishable from malignancy on cross-sectional imaging. Although several single case reports describe this entity, no radiology-focused multi-case series has been previously published. We present 3 patients referred to a regional sarcoma service with abdominal wall masses initially suspected to represent soft-tissue sarcoma. All 3 underwent multimodality imaging, which demonstrated heterogeneous, enhancing abdominal-wall lesions with associated inflammatory change. In each case, thin-slice CT ultimately identified a subtle linear hyperdense structure, corresponding to a migrated fish bone traversing or lying adjacent to bowel, establishing the correct diagnosis of foreign-body-induced phlegmon. MRI appearances were non-specific and mimicked neoplastic processes. Management varied from conservative antibiotic therapy to incision and drainage, with all patients making a full recovery and no recurrence. This case series highlights a rare but significant radiologic pitfall in the assessment of abdominal wall masses. Key learning points include scrutinizing CT in thin slices and bone windows for linear calcified foreign bodies, recognizing that MRI and PET-CT may mislead toward malignancy, and maintaining foreign-body phlegmon within the differential diagnosis for atypical abdominal wall "tumours." Awareness of this entity can prevent unnecessary biopsies, oncologic referrals, and radical surgeries.