Multidetector CT of expected findings and early postoperative complications after current techniques for ventral hernia repair

Broadly defined as “a protrusion of tissues through a defect of the anterior abdominal wall”, ventral hernias represent a highly prevalent but heterogeneous problem in general surgery. The European Hernia Society (EHS) categorizes abdominal wall hernias as either primary or incisional. The former group includes midline (epigastric and umbilical) and lateral (spigelian and lumbar) hernias, which are classified according to their size (<2 cm, >4 cm, or intermediate). Congenital or acquired umbilical hernias represent the most common primary hernias [9].

An incisional hernia is defined as “any abdominal wall gap with or without a bulge in the area of a postoperative scar perceptible or palpable by clinical examination or imaging from incisional hernias”. Incisional hernias develop after any abdominal surgery, with an incidence approaching 20 %, and are increasingly encountered because of increased life expectancy and the high prevalence of risk factors such as obesity and diabetes. Recurrences after repair of primary hernias fall in the incisional group [9].

Indications for VHR include pain, cosmesis, and prevention or treatment of complications such as bowel obstruction and strangulation [1, 2]. At our hospital, the mean case volume approaches 110 VHR procedures each year; the vast majority (85–90 %) are for incisional hernias.

Before the availability of modern PMs, the rate of postoperative hernia recurrence approached 50 %. Current techniques for VHR rely on PM implantation, may be performed during either open surgery or – increasingly – laparoscopic surgery, and consistently achieve favourable results with minimal perioperative morbidity (3.7 % overall complication rate) and limited (7.5–10 %) recurrence rate [1, 3, 4, 10‐12].

Open VHR is recommended for large (>10 cm) abdominal wall defects. The sublay-mesh (Rives–Stoppa) procedure remains the preferred open technique to treat ventral (particularly incisional) hernias. Following skin incision, the surgeon opens the hernial sac, dissects the anterior abdominal structures up to the preperitoneal space, and removes the previous surgical scar, adhesions in the abdominal cavity and the hernial sac itself. The PM is then implanted extraperitoneally in the newly formed space, interposed between the posterior rectus sheath and rectus muscle. Very large hernias with lateral displacement of the rectus abdominis muscles require open repair with the intraperitoneal onlay-mesh (IPOM) technique: after exposure and opening of the hernial sac, adhesions between the abdominal wall and intestinal loops are detached, the hernial sac is removed, and a large PM is positioned from the inside over the breach [10‐14].

Conversely, laparoscopic VHR involves creation of pneumoperitoneum, introduction of instruments through the trocar ports, and reduction of herniated bowel loops into the peritoneal cavity. The PM is placed intraperitoneally over the defect, without excision of the hernia sac [15].

With either approach, sutures, fixation screws or an additional second PM may be used to reinforce the repair. Thorough yet easy-to-understand step-by-step graphical explanations of the open and laparoscopic techniques described above are freely downloadable from the dedicated www.​herniamed.​de website [13‐15].

A proliferation of mesh products for VHR are currently available. The most common PMs are made of polypropylene (PP) or expanded polytetrafluoroethylene (ePTFE). Both types are invisible on plain radiographs, and sonographically appear hyperechoic with posterior acoustic shadowing. Visualization of PMs by CT is highly variable, depending on the intrinsic density, thickness, woven or nonwoven, knitted or not-knitted structure, and surrounding inflammatory reaction [20].

Monofilament, double-filament (such as Prolene; Ethicon, Inc., Somerville NJ-USA), and multifilament (such as Surgipro; Covidien, Minneapolis MN-USA) PP PMs are thin and isoattenuating to muscles and, therefore, generally invisible or hardly differentiated from the deeper fascia of the rectus abdominis muscles and parietal peritoneum (Fig. 1). Conversely, thicker ePTFE PMs (such as the Gore-Tex Dual-Mesh; W.L.Gore & Associates, Inc., Flagstaff, AZ–USA) are consistently recognized as hyperdense lines behind the muscles of the abdominal wall (Figs. 2 and 3). Finally, composite PMs including an ePTFE component (such as the Bard Composix; Bard Davol Inc., Warwick RI-USA) are less consistently recognizable. Visualization of faintly hyperattenuating PMs may be improved by the use of maximum-intensity projection (MIP) reconstructions (Fig. 2c). When present, metallic surgical staples or tacks used for mesh fixation are easily visible (Figs. 2 and 3). Additionally, three-dimensional volume-rendering images effectively visualize the position, spatial configuration, and reticular structure of the PM (Fig. 3) [5, 6, 8].

In the early postoperative setting, suction drains may be in place, and their position should be reported. Hours or a few days after recent laparoscopic VHR, some residual intraperitoneal gas is commonly observed. Similarly, mild to moderate subcutaneous emphysema from insufflation into the abdominal wall during trocar passage generally does not represent a complication, provided there are no clinical or laboratory findings suggesting peritonitis or necrotizing fasciitis [8].

Postoperative seromas develop at the operated anterior abdominal wall in almost 10 % of patients. After open VHR, serous fluid collects in the retromuscular–prefascial space; conversely, following laparoscopic surgery, seromas result from peritoneal fluid flowing through the porous PM and accumulating within the residual hernia sac [8, 11, 12, 21].

At CT, serous collections may have different shapes (globular, multiloculated, or tubular). Seroma is confidently diagnosed when a collection shows fluid attenuation and does not enhance. Unfortunately, in the early postoperative days, identification of air-fluid levels and thin reactive peripheral enhancement (Fig. 4) was not unusual. In this case, differentiation from an abscess is challenging and relies on correlation with clinical and laboratory findings. Conversely, a thick or irregular enhancing “rim” should suggest infection rather than seroma [5, 6, 8].

Seromas should be managed conservatively unless they are large, painful, or persistent after 4–6 weeks, and aspiration is contraindicated to prevent superinfection [3, 4, 8, 21].

Although post-VHR iatrogenic complications are reported in up to 18–25 % of patients overall, the majority of cases are minor and do not require hospitalization or specific treatment. The commonest specific complications include infection, small bowel obstruction, and haemorrhage, in descending order of frequency [3, 4, 11, 12].