Colon: Neoplastic Disease: CT of Cecal Volvulus: Unraveling the Image
Volvulus of the cecum is a torsion of the bowel about its own mesentery often resulting in a closed loop obstruction. Cecal volvulus can only occur in a small percentage of the population (11-25%) who have a developmental failure of peritoneal fixation, allowing the proximal colon to be free and mobile [1]. The second requirement is restriction of the bowel by a fixed point within the abdomen, which serves as a fulcrum for rotation such as an adhesion, abdominal mass, or scarring from calcified lymph nodes [2]. It is critical to recognize the CT signs of cecal volvulus because the clinical examination is often vague and CT is usually the imaging technique of choice in patients presenting with acute abdominal pain [3]. Furthermore, the diagnosis may be obscured on plain abdominal films because the closed loop obstruction is filled with fluid, orientated in an anteroposterior plane, or obscured by overlapping loops of air distended bowel [4]. CT reveals the presence and location of the volvulus with the added benefit of early identification of potential fatal complications such as ischemia and perforation. Three-dimensional reconstructions may further improve diagnostic capabilities by allowing visualization of the entire bowel in a single image.
Clinical Background
Cecal volvulus accounts for 11% of all intestinal volvulus, generally presenting in younger patients of ages 30-60. Medical history may include prior abdominal surgery, pelvic mass, violent coughing, atonia of the colon, extreme exertion, unpressurized air travel, and third trimester pregnancy [1]. Patients present with nausea, vomiting, constipation, and acute cramping pain [1]. The clinical differential diagnosis is usually bowel obstruction versus appendicitis, inflammatory bowel disease, irritable bowel syndrome, or peptic ulcer disease [1].
The Two Types of Twists
When torsion of bowel results in obstruction, the term "volvulus" is imployed. About half of the time the cecum twists in the axial plane, rotating clockwise or counterclockwise about its long axis and appearing in the right lower quadrant [3, 5] The other half of cases are known as the loop type in which the cecum both twists and inverts, occupying the left upper quadrant of the abdomen [3, 5] . The terminal ileum is usually twisted along with the cecum and identification of a gas filled appendix confirms the diagnosis [5]. There is a variant of cecal volvulus termed a cecal bascule. This occurs when the cecum folds anteriorly without any torsion. Cecal bascule is often seen as a dilated loop in the mid abdomen [3].
The "Coffee Bean," "Bird beak," and "Whirl Sign"
On axial CT, the diagnosis of cecal volvulus is suggested by the extreme dilatation of the cecum. When seen on conventional radiograph or a tomogram, the cecal volvulus is seen as a rounded focal collection of air distended bowel with haustral creases which resemble the appearance of a coffee bean. The two limbs of the looped obstruction gradually taper and converge at the site of the torsion resembling a bird’s beak. This "bird beak" sign, originally described for sigmoid volvulus on conventional radiograph, can also be appreciated on axial CT images of the loop type cecal volvulus [4] . A specific CT sign for volvulus is known as "the whirl" . This has been described in volvulus of the midgut, cecum and sigmoid colon [2, 4]. The whirl is composed of spiraled loops of collapsed cecum and distal ileum. Low attenuation fatty mesentery with enhancing engorged vessels radiate from the twisted bowel. In the central eye of the whirl, a soft tissue density pinpoints the source of the twist [2]. The degree of cecal rotation can even be predicted by the tightness of the whirl [6].
Treatment
Colonoscopy has been shown to have a high rate of diagnosis and reduction in cases of sigmoid volvulus, but is often not ideal in treating volvulus of the cecum. Reduction rates by colonoscopy are much lower in treating cecal volvulus and there is a recurrence rate exceeding 50% [1]. In cases of uncomplicated cecal volvulus, surgical options include cecopexy which has a low rate of morbidity (0-8%) and volvulus recurrence. Gangrene or perforation requires surgical resection which eliminates the possiblility of recurrence and also has a low morbidity and mortality [1, 7]. CT findings change patient management by the demonstration of the signs of bowel ischemia which include thickening of bowel wall, mesenteric hemorrhage and pneumatosis intestinalis [1].
The Role of Three Dimensional Imaging
Diagnosing the etiology of bowel obstruction on axial images requires following multiple changing caliber loops of air distended bowel over many consecutive images. When the bowel collapses or orients in an anteroposterior direction, visualization of the bowel becomes limited and it is difficult to exactly locate the transition point. The use of barium enema circumvents this problem by isolating the involved loop and accurately demonstrates the point of obstruction. However, barium enema is somewhat limited because it may yield no information about emergent complications like bowel ischemia or other disease processes outside the bowel wall. 3-D imaging is ideal because like a barium enema, the entire bowel can be visualized in a single image, separating the volvulus from other dilated loops . 3-D displays allow selection of the most optimal plane for viewing the volvulus and help to precisely locate the source of the torsion . In effect, the ability to analyze an image in multiple planes, allows one to unravel twisted bowel and confirm the diagnosis of volvulus.