Case 94 - Pseudotumor due to muscle transposition

Summary

Imaging description

Muscle flaps may be used to protect surgically debrided femoral vessels in the groin. The transposed muscle, commonly the sartorius or rectus abdominis, results in a soft-tissue mass anterolateral or anterior to the femoral vessels on postoperative imaging that can be potentially confused for a postoperative collection or tumor recurrence (Figures 94.1 and 94.2) [1].

Importance

Misidentification of a transposed muscle as a postoperative collection or recurrence may result in unnecessary workup and treatment.

Typical clinical scenario

Muscle transposition may be performed after radical inguinal lymphadenectomy, debridement of open groin wounds, or repair of infected femoral artery grafts [1–3]. This pitfall is typically seen when a surgical patient is scanned for evaluation of postoperative fever or other complications, or when a patient who has had a radical lymphadenectomy for malignancy such as melanoma undergoes surveillance imaging.

Differential diagnosis

Absence of the normal muscle is a critical observation in establishing the imaging diagnosis of muscle transposition. The contralateral side can be used as an internal control for this purpose. In the early postoperative period, the lack of a rim-enhancing capsule helps distinguish a muscle flap from an abscess. Later, continuity and isodensity with the sartorius muscle inferiorly or the rectus abdominis superiorly and lack of typical masslike features help distinguish muscle transposition from tumor recurrence.