MRI of surgical flaps in pelvic reconstructive surgery: a pictorial review of normal and abnormal findings

Surgical flaps are commonly used for pelvic reconstruction in a subgroup of patients with locally advanced or recurrent anorectal and gynecologic malignancies and following complications of pelvic irradiation. Surgical scenarios where flaps may be placed include (but are not limited to) extended or radical abdominal perineal resection (APR) and total pelvic exenteration (PE). Surgical flaps in pelvic reconstruction serve several functions, including reducing dead space and providing structural support, facilitating wound closure and cosmetic appearance, enhancing the postsurgical healing process, protecting anastomoses and helping to prevent adhesions of organs and viscera to adjacent structures and the pelvic side wall. The most commonly used surgical flaps in pelvic reconstruction surgery include the VRAM (Vertical Rectus Abdominis Muscle), MRAM (Modified Rectus Abdominis Myocutaneous flap), gracilis, sartorius and omental flaps. Surgical flaps can be mistaken for recurrent or residual tumor by radiologists who are not familiar with the appearance or surgical methods of flap placement, since flaps may have a mass-like appearance on cross sectional imaging, including CT and MRI. Recurrent neoplasm may be difficult to differentiate from postoperative changes of flap placement and associated postsurgical anatomic distortion. This review article focuses on understanding the nuances of surgically placed pelvic flaps and identifying their normal and abnormal appearances on magnetic resonance imaging (MRI) along a time continuum. Postsurgical complications, including hematoma, postoperative fluid collections, infection, ischemia, and necrosis as well as tumor recurrence on the initial and follow-up magnetic resonance imaging are illustrated and discussed.