Mesh complications often present with subtle imaging findings, and may require knowledge of the operative technique utilized to diagnose definitively. US does not reliably identify the mesh, especially if it is folded, balled up, or otherwise complicated (Fig. 19.3). As such, US is not recommended as a first-line imaging modality to evaluate the postoperative groin after mesh implantation when the integrity of the mesh itself is in question. Due to the combination of low material density and minimal profile, normal mesh material is often indistinguishable from surrounding tissue on CT [2], requiring the radiologist to discern a postoperative state from the presence and location of the patient’s surgical scars (Fig. 19.4). Even in states of chronic inflammation (e.g., mesh reaction), it may be impossible to specifically identify pathology on the basis of CT alone. On MR, flat mesh materials appear as dark linear bands on T1 sequences, slightly thicker than normal fascial planes, but may be more difficult to identify among their surrounding tissues on fluid-sensitive sequences (Fig. 19.5).

Normal mesh should appear smooth, and wrinkling may represent migration with subsequent focal recurrence or inflammatory response. While mesh may be fixed in position with sutures, staples, or tacks, shifting of mesh material may occur. If slippage does occur, even partial mesh migration may result in gross recurrence of bowel protrusion, or may present as subtle herniation of peritoneal or preperitoneal fat. Interposition of even small amounts of fat between mesh material and the abdominal wall may be a cause of significant pain. Dynamic MR sequences are particularly capable of identifying such pathology, which may be missed by CT.

Pain associated with more complex mesh materials such as plug or sandwich designs are uniquely challenging to diagnose, as many radiologists are not aware of the existence of such materials and may not be able to recognize normal postoperative appearance without access to detailed operative notes or direct communication by the referring physician. Volume-occupying materials utilized in repair of large, patulous defects often incorporate significant biological material into their interstices, appearing on imaging as large pseudomasses and resulting in misdiagnosis (Fig. 19.6). As an example, our own personal case series includes a post-herniorrhaphy patient with significant pain who underwent percutaneous biopsy of “bilateral inguinal masses” that were in fact mesh Perfix^TM plugs that were impressing upon the contents of the inguinal canal, resulting in testicular venous congestion and chronic pain. Most plugs are found within the inguinal canal with a cone appearance, and conversion to a different shape (especially a narrow needle-like one) may be indicative of abnormality, suggesting migration as an etiology of groin pain. When properly positioned, sandwich mesh, such as the Prolene^TM Hernia System , should be seen on MR as a T1 dark band superficial to the internal inguinal ring or direct fascial defect, with a second layer positioned preperitoneally: the presence of fat between the layers represents normal appearance.