Imaging the postoperative patient: long-term complications of gastrointestinal surgery
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The objectives of this review are (1) to become acquainted with the long-term complications of surgery of the gastrointestinal tract, and (2) to appreciate the appropriate use of imaging in the assessment of long-term complications.
Gastrointestinal tract surgery comprises a group of procedures performed for a variety of both benign and malignant diseases. In the late postoperative setting, adhesions and internal hernias are the most important complications. and they can be further complicated by volvulus and ischemia. At present, computed tomography (CT) is the workhorse for evaluating late postoperative complications. Accurate imaging assessment of patients is essential for adequate treatment planning.
Imaging findings or procedure details
In this pictorial essay we will review the most frequent long-term complications after gastrointestinal surgery, including adhesions, afferent loop syndrome, closed-loop obstruction, strangulated obstruction, internal hernias, external hernias, anastomotic strictures and disease recurrence. Examples will be depicted using iconography from the authors’ imaging department.
Knowledge of the most frequent complications after gastrointestinal surgery in the late postoperative period is of paramount importance for every radiologist, so that potentially life-threatening situations can be promptly diagnosed and adequate therapy can be planned.
• Long-term postoperative complications of gastrointestinal tract surgery can be divided into procedure-related and disease-related categories.
• The most common procedure-related complications are internal hernias and adhesions.
• The most frequent disease-related complications are mainly associated with neoplastic or inflammatory recurrence.
• Computed tomography is the most useful examination when such complications are suspected.
KeywordsPostoperative complications Intestinal obstruction Afferent loop syndrome Abdominal hernia Surgical adhesions
An acquaintance with the types of surgery, including the most common anastomosis, and with their most frequent complications are the first steps in preventing misdiagnosis of potentially life-threatening complications following gastrointestinal surgery.
The radiologist is often faced with altered anatomic findings that hamper the ability to differentiate between an expected postoperative finding and a real complication. Therefore, communication with the referring surgeon is strongly advised in such situations before performing a diagnostic examination.
Gastrointestinal contrast studies are more commonly used to look for immediate postoperative complications, such as intestinal leak or anastomotic dehiscence.
Computed tomography (CT) is currently the workhorse for evaluating late postoperative complications, with the exception of magnetic resonance imaging (MRI) for suspected recurrence of rectal cancer or inflammatory bowel disease.
Long-term postoperative complications of GI tract surgery
• Herniation (internal and external)
• Afferent loop syndrome
• Anastomotic strictures
• Neoplastic recurrence
• Inflammatory bowel disease recurrence
Adhesions and internal hernias are the most important procedure-related complications in the late postoperative period, and can be further complicated by volvulus and ischemia. Anastomotic strictures are also relatively frequent following GI tract surgery.
Disease-related complications are typically related to disease recurrence involving both neoplastic and inflammatory conditions.
These hernias can be either congenital or acquired. The major classifications of internal hernias include paraduodenal (53 %), pericecal (13 %) and transmesenteric hernias (8 %), hernias through the foramen of Winslow (8 %) and intersigmoid hernias (6 %) [2, 4].
Although paraduodenal hernias are classically regarded as the most prevalent, the incidence of transmesenteric hernias (TMH) has been growing given the increased number of operative procedures that involve Roux-en-Y surgery, such as gastric bypass surgery and liver transplants [2, 3]. In fact, IH are almost as frequent a cause of obstruction as adhesions in patients who receive liver transplants with Roux-en-Y anastomosis confection .
Clinically, IH can be asymptomatic, or cause nonspecific intermittent abdominal pain or full-fledged strangulated obstruction (the most common presentation). As these hernias are difficult to identify clinically, imaging plays a pivotal role in their evaluation. Herniation of the bowel loops through the defect can be a transient phenomenon that can further confound diagnosis. Clinical or imaging evaluation performed during a symptomatic period is more likely to reveal the abnormality .
Transmesenteric hernias are particularly prone to complications (volvulus and strangulation), and symptom onset is usually more acute than in other types of internal hernias [2, 6]. They occur in the adult population who has had abdominal surgery, especially Roux-en-Y surgery, which is now the most frequent type of acquired internal hernia according to a recent study [2, 3, 6]. Transmesenteric internal hernias can be divided into three groups: through a defect in the transverse mesocolon with retrocolic Roux limb (the most common type), through a defect in the small-bowel mesentery at the jejuno-jejunal anastomosis, and posterior to the Roux jejunal loop (Peterson defect) [7, 8].
It is important to differentiate small-bowel obstruction (SBO) due to internal hernia from obstruction due to adhesions, since the former requires emergent surgical treatment . A combination of clinical and imaging criteria can help distinguish between the two. In SBO secondary to adhesions, an abrupt angulation of a bowel segment is more likely to occur. Small bowel obstruction due to IH tends to present much longer after surgery, and a collection of dilated small-bowel loops lying adjacent to the abdominal wall, without overlying omental fat and with central displacement of the adjacent colon, associated with crowding, distortion, and engorgement of mesenteric vessels, is seen on CT . A cluster of loops of small bowel cephalic to the transverse mesocolon between the stomach and spleen in the left upper quadrant is typical of the transmesocolic subtype, and a group of small-bowel loops in a peripheral abdominal location is typical of the transmesenteric jejuno-jejunal type [7, 10]. The Peterson type of TMH has no distinctive findings, but because the herniation most often occurs from right to left, there may also be a cluster of dilated loops in the left upper quadrant [2, 7].
Multi-planar reformation (MPR) oriented to the “intestine-mesentery-directed plane” and vertical to this plane should be performed in order to increase the likelihood of detection of the hernial orifice. This can be identified as an area where the mesentery of the closed loop converges on a given multiplanar view; on the plane vertical to the affected intestine, the hernial orifice shows a round/oval configuration of the converged mesentery .
Left-sided paraduodenal IH is the leading differential diagnosis of TMH, but has different distinctive characteristics, such as a sac-like mass of dilated bowel lateral to the ligament of Treitz that displaces and indents the transverse colon and stomach .
Volvulus and ischemia of the herniated small bowel are frequent complications of TMH. Typical findings of strangulated closed-loop obstruction are seen (whirl sign, engorged blood vessels, mesenteric edema, ascites and bowel wall thickening) .
Closed-loop bowel obstruction and incarceration
A closed-loop bowel obstruction or incarceration is a type of mechanical intestinal obstruction in which a segment of bowel is occluded at two separate points along its length, almost always adjacent to each other, as the result of a single constrictive lesion. This anatomical configuration can lead to twisting of the loop along its long axis, and thereby produce a bowel volvulus, with subsequent compromise of the vascular supply and ischemia—strangulating obstruction. Although incarceration and strangulation are related phenomena, incarceration may occur without strangulation and may resolve spontaneously .
Closed-loop obstruction is most commonly caused by postoperative adhesive bands, and is less frequently due to internal or external hernias .
- The beak sign, representing the beak-shaped morphology of the dilated loop toward the obstruction, when imaged in a longitudinal orientation (Fig. 2)
The whirl sign, which corresponds to the whirled appearance of the mesenteric vessels in the middle of the obstruction point (Fig. 2). The tightness of the whirl pattern reflects the degree to which the mesentery and vessels are rotated. Although hampered by low sensitivity (60 %), a recent study has shown that if this sign is present on a CT scan, a patient is 25 times as likely as a patient without it to undergo surgery [13, 14].
- A radial distribution, which refers to stretched mesenteric vessels converging toward the central point of obstruction (Fig. 3).
Multiplanar reformatted images may prove decisive in achieving correct diagnosis of a closed-loop obstruction .
CT findings of strangulated obstruction include wall thickening, altered pattern of enhancement of the bowel wall, dilated mesenteric veins, mesenteric edema, ascites, pneumatosis intestinalis, pneumatosis portalis and pneumoperitoneum.
The most common CT finding in bowel ischemia, although nonspecific, is bowel wall thickening. It is caused by mural edema (low attenuation before contrast administration), hemorrhage (high attenuation before contrast administration) and/or superinfection of the ischemic bowel wall. If unenhanced CT is not performed prior to contrast-enhanced CT, the ability to differentiate between intramural hemorrhage and hyperemia and/or hyperperfusion is impaired .
On contrast-enhanced CT, a highly specific but less sensitive finding is absent or diminished parietal contrast enhancement. In some cases, prolonged enhancement due to delayed return of the venous blood, with subsequent slowing of the arterial supply, can also be seen .
Clinical and laboratory differentiation between simple obstruction and incarceration/ strangulation is very difficult, and treatment delay is a major prognostic factor for increased morbidity and poor survival. CT is extremely useful in discriminating between these two entities, and it plays an instrumental role in determining appropriate patient treatment (medical versus surgical). Findings of closed-loop obstruction should result in close monitoring, and if clinical symptoms persist, early surgery is suggested. In patients in whom signs of strangulation are already evident, emergency surgery is mandatory .
Stomal and parastomal hernias are a subtype of incisional hernias that involve herniation of the bowel or the mesentery at the site of or adjacent to a stoma . Even after closure of the enterostomy, the ostomy site can remain a potential area of herniation . Most parastomal hernias occur within 8 months of surgery. The etiology is multifactorial and includes characteristics such as obesity, malnutrition, increased intra-abdominal pressure and chronic respiratory disease .
Parastomal hernias are quite common, with an expected prevalence of 33–78 %, depending on clinical or CT evaluation. However, unless obstruction, perforation or stoma malfunction occur, there is no need for surgical repair [19, 20, 21, 22].
Parastomal hernia CT classification
Peritoneum follows the wall of the bowel, with no sac formation
Only bowel forming the colostomy, with a sac <5 cm
Hernial sac containing only bowel forming the colostomy, with a sac >5 cm
Hernial sac containing omentum
Hernial sac containing intestinal loop other than the bowel forming the stoma
Adhesive bands are funiculate structures that form between the peritoneum of tissues and organs, often as a result of injury during surgery. They are composed of fibrous tissue and abundant fat .
Adhesions are the most common cause of bowel obstruction after surgery, and they constitute the leading cause of long-term reoperation following abdominal and pelvic surgery.
Bowel loops that pass through the orifice between the adhesive band and the peritoneum form a type of internal hernia that can evolve to closed-loop obstruction. CT findings in this situation are similar to those in other internal hernias (cf. "Internal hernias"). Overt obstructive small-bowel disease related to adhesions can be further subdivided into simple obstruction and closed-loop or strangulated obstruction .
Nevertheless, a non-obstructive subtype can also be found. These patients may have intermittent or low-grade small-bowel obstruction, for which CT has poor sensitivity. CT enteroclysis or dynamic MRI may be important options for better demonstrating the transition point [8, 23].
Small-bowel obstruction caused by adhesions almost always requires surgery. When intestinal strangulation supervenes, immediate abdominal surgery is mandatory. However, the risk of additional adhesions increases as the number of surgeries increases.
Afferent loop syndrome
Afferent loop syndrome (ALS) represents mechanical obstruction of the afferent loop, occurring in 0.3–2 % of gastroenterostomies, both in Billroth II surgery (the duodenum is the afferent loop) and Whipple or Roux-en-Y procedures (the Roux segment is the afferent loop) [9, 24, 25].
Most cases of ALS are due to adhesions, internal hernia, anastomotic stricture or recurrent tumor . It can also be secondary to preferential gastric emptying into the afferent loop due to abnormal surgical anastomosis or because of efferent loop obstruction resulting in fluid accumulation at the afferent loop [24, 26]. The back pressure from the dilated afferent loop can cause biliary dilatation and acute pancreatitis .
The diagnosis may not be clinically suspected, as ALS may present many years after the initial surgery .
The incidence of anastomotic strictures depends on the type of surgery performed. The causes for the stricture are not yet clearly understood. For example, in gastric bypass patients, it is thought that the period of time during which the anastomosis is exposed to an inappropriately large volume of gastric acid results in ongoing inflammation, ulceration and stricture formation . Several studies also suggest an increase in the incidence of strictures with the use of stapler versus handsewn anastomosis, both for gastrojejunostomy and colorectal anastomosis [1, 29]. For ileal pouch anal anastomosis, a meta-analysis found an incidence of anastomotic strictures of 9.2 % .
The resulting symptoms reflect the degree of luminal stenosis, and include abdominal pain, distention, nausea and vomiting.
CT has become increasing important when an anastomotic stricture is being considered, and is now the preferred imaging modality in this particular setting, since it is able to demonstrate not only the anastomotic abnormality but extra-wall structures as well . CT findings include focal bowel wall thickening at the anastomosis and distended proximal bowel loops filled with fluid or desiccated stool  (Fig. 17b).
Depending on the location, strictures can be treated with manual/endoscopic dilation or surgery .
Tumor recurrence can be the cause of obstruction several months or years after surgery.
CT is the modality of choice in this setting, as it clearly shows an enhancing mass or asymmetric wall-thickening near the site of the initially resected tumor.
Inflammatory bowel disease recurrence
Most patients with Crohn’s disease (CD) require surgery at some point in their lives, and can develop relapses either at the intestinal anastomosis or far from it, at any other segment of the GI tract. These relapses can occur in the form of new strictures, fistulae or abscesses .
A combination of symptom assessment plus endoscopy is still the gold standard for assessment of recurrence in postoperative CD patients .
CT enterography/enteroclysis should be the first radiologic procedure performed in patients with acute symptoms when recurrence is suspected. MR enterography/enteroclysis is increasingly being considered as the first-choice examination in acute exacerbation in a child or young adult with known CD, because it is a radiation-sparing technique in a patient who will likely be subjected to multiple serial examinations . MRI is also the technique of choice for the diagnosis and characterization of perianal fistulae.
Ulcerative colitis is normally continuous from the rectum to the colon. Total proctocolectomy is the definitive treatment for the disease, but two other types of surgery are usually performed to obviate the disadvantages of a permanent colostomy.
Patients who receive total colectomy with ileorectal anastomosis are at risk for disease recurrence at the rectum, and thus clinical and endoscopic follow-up are advised. When proctocolectomy with ileal-anal pouch is chosen, there is an increased probability of the patient developing pouchitis (ileal pouch inflammation). The diagnosis depends on clinical, endoscopic and histopathological data, and there is usually no role for diagnostic imaging in this setting .
In conclusion, knowledge of the normal appearance of the abdomen and pelvis after GI tract surgery is mandatory for every diagnostic radiologist, particularly in an emergency setting. An acquaintance with the most frequent complications in the late postoperative period, such as bowel obstruction due to internal or external hernias, adhesions, afferent loop syndrome and disease recurrence, is of paramount importance.
Communication with the referring surgeon can be a valuable adjunct for achieving diagnosis in potentially life-threatening situations so that adequate therapy can be planned.
- 28.Subhani M, Rizvon K, Mustacchia P (2012) Endoscopic evaluation of symptomatic patients following bariatric surgery: a literature review. Diagn Ther Endocrinol 753472. doi: 10.1155/2012/753472
- 33.Expert Panel on Gastrointestinal Imaging (2011) ACR Appropriateness Criteria for Crohn disease American College of Radiology (ACR), Reston (VA): Available via http://www.guideline.gov/content.aspx?id=35137
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