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Primary torsion of the greater omentum. An obscure and unusual cause of acute abdomen
B. Papaziogas, D. Dragoumis, P. Tsiaousis, D. Giakoustidis, S. Atmatzidis, G. Sarlis, K. Atmatzidis (Chirurgia, 102 (1): 95-98)
Introduction
Primary omental torsion is an unusual cause of acute abdominal pain, often mimicking other variable acute abdominal conditions. However, it should not be overlooked in the differential diagnosis of acute abdomen. Although recently the use of computed tomography has demonstrated significant success in the preoperative detection of this pathology, the diagnosis of primary omental torsion is rarely made before the patient reaches the operative table. This report describes a case of primary segmental omental torsion and discusses thoroughly the diagnostic and therapeutic implications of this unusual entity.
Case Report
A 36-year-old man presented to the emergency unit complaining of a persistent and gradually increasing diffuse abdominal pain of 3 days duration. The pain started off suddenly, just after the completion of a heavy meal. No previous surgical operations and no intake of medications were referred. On physical examination the patient had a low-grade fever of 37.5°C with localized tenderness, guarding and slight rebound tenderness in the right upper quadrant was found, but no mass was palpable. The white blood cell count was mildly elevated to 12,200/mm3, whereas urinalysis and biochemical tests were within the normal limits. Signs and symptoms suggested an intra-abdominal entity, such as a retrocecal appendicitis, viscous perforation or acute cholecystitis. Plain abdominal X-rays revealed no abnormalities, while urgent ultrasonography of the abdomen was negative for free fluid, mass, and signs of cholecystitis. A contrast-enhanced CT scan of the abdomen and pelvis showed diffuse inflammation in the omental fat on the right side of the abdomen. There was no thickening of the adjacent bowel walls or abscess formation (Fig. 1).
The patient was observed for 8 hours during which time, there were no signs of improvement in his clinical condition. Due to the persisting pain he eventually underwent surgical operation with a lower right paramedian incision. At the intraperitoneal exploration, the appendix was normal. When the incision was extended, there was found an omental volvulus overlying the ascending colon and omentectomy was performed. The macroscopic examination revealed an omental twist with four complete clockwise rounds, with diffuse areas of thickening and tan brown discolorations (Fig. 2). No parietal adhesions of the mass to the hernia openings or abdominal organs were noted. An appendectomy was also performed.
A segment of omentum measuring approximately 10cm was submitted for pathologic examination. The histologic essay reported extensive fat necrosis, vascular congestion and non-specific inflammatory infiltration, but no other pathology was found. The appendix showed no inflammation reaction. The recovery was uneventful and the patient was discharged on the sixth postoperative day.
Figure 1
Figure 2

Discussion
The greater omentum is a wide sheet of peritoneum, which hangs from the greater curvature of the stomach to the adjacent organs. It is connected more steadily with the organs on the left side of the abdomen and attaches itself to the diaphragm. The greater omentum grows from the greater curvature of the stomach and forms the four layered, fat-laden omental apron. Because of an increasing deposition of fat onto the greater omentum and its inferior extension throughout the years, the almost thin and transparent omental membrane in the neonate becomes thick and fatty in the adult life (1, 2). Torsion of the omentum is a rather unusual condition, usually diagnosed during laparotomy for an acute abdomen and occurs when the omentum twists around its long axis, causing venous obstruction, oedema, and vascular compromise.
Omental torsion, unrelated to any other intra-abdominal lesion, was first reported by Eitel in 1899. Its etiology is indistinct, and it can be classified as primary or secondary, the latter being the more common. Torsion of the omentum is referred as secondary, only when a specific cause of torsion is found. When no predisposing abnormality is prominent, omental torsion is considered primary.
Primary omental torsion is unipolar; that is, a free and movable segment of omentum exists at one end and a fixed point at the other end, around which twisting occurs. On the contrary, secondary omental torsion is characterized by its bipolarity, which means that both ends of the omentum are firmly fixed. The distal end of the omentum is attached to scars, due to previous surgery or trauma, inflammation, cysts, tumors, hernias, or any intra-abdominal conditions, that may favor the formation of adhesions (1, 2).
Predisposing factors that lead to omental torsion include anatomical malformations of the omentum, such as a bulky, bifid omentum or tongue-like projections. Essential variations in omental fat distribution, particularly in obese patients, have been cited as a triggering cause of primary omental torsion. The amount of fat present in the omentum is reflected in the body habitus. It is strongly postulated that increased fat deposit in obese people outstrips the blood supply to the developing omentum, leading to either relative ischemia as the inciting event, increased omental weight leading to torsion, or traction to the most distal parts of the omentum. In addition, constructive anomalies of the omental blood supply are also related to primary omental torsion. In that case, the omental veins become more enlarged and devious than the arteries, allowing venous irregular kinking and obtaining a fixation point around which an omental segment can twist (1, 2, 3).
In most cases of omental torsion, the omentum is found twisted around the distal right epiploic artery, resulting in right-sided abdominal pain (90%). The higher incidence of right-sided omental torsion is probably attributed to its mobility and greater length compared to the left omentum.
Several precipitating factors have been involved in the pathogenesis of primary omental torsion. Such factors, having a causal relationship with both primary and secon-dary omental torsion, include local trauma, occupational use of vibrating tools or sudden increase in intra-abdominal pressure after heavy meals, heavy exertion, changes in body position, coughing or sneezing. It is possible that hyperperistalsis, following a heavy meal, induces omental displacement leading to omental torsion, as occurred in our patient. Whatever the cause may be, subsequent vascular impairment can follow the twisting of the omentum and the haemorrhagic infarction and fat necrosis of the omental segment will be the eventual progress. However, sometimes infarction may be present without signs of torsion at surgery. This may be associated with some possible predisposing factors, e.g., congestive heart failure, digitalis administration and occlusive vascular disease (1, 2, 3).
Torsion of the omentum affects patients of any age, mainly young and middle-aged adults (30-50 years old), but it has also been described in children above the age of 4 years. According to published reports of the last 15 years, there is a 3:1 predilection for males (3).
The typical clinical appearance of omental torsion, but by no means specific, is right lower quadrant or right para-umbilical pain of sudden onset and short duration (24-48 hours), which is usually constant, nonradiating and gradually increases in intensity. Gastrointestinal symptoms, such as nausea, anorexia, and vomiting, are uncommon. Usually a mild fever (~37, 5ºC) is present, and there is a slight elevation on white blood cell count (WBC) and C-reactive protein (CRP). Neither the symptoms nor the physical findings present any characteristic pattern that would suggest the diagnosis, as all of these features are common to several other acute abdominal diseases. Possible suspected diagnoses include acute appendicitis, acute cholecystitis, cecal diverticulitis, cecal or epiploic appendagitis or viscous perforation, and the final diagnosis in the majority of cases is made during the surgical procedure (2, 3).
Plain films of the abdomen and sonographic findings are non-specific in most cases of omental torsion. If there is involvement of a majority of the omentum, small bowel obstruction may develop. A typical ultrasound scan appea-rance has also been described, with the infracted omentum appearing as a moderately hyperechoic, noncompressible, ovoid intra-abdominal mass adherent to the anterior abdominal wall with localized point tenderness (4).
Because the clinical findings are obscure, CT findings of omental torsion should be searched carefully for an accurate diagnosis. The key to the preoperative diagnosis of omental torsion is the identification of concentric, hyperattenuating linear strands, which are characteristic; this important radiological sign is not present in other omental diseases. This "pedicle sign" may not be as apparent, if the axis of rotation is not perpendicular to the transverse scanning plane. A similar whirling pattern may also be seen in small bowel volvulus, but it is usually associated with small bowel obstruction and is centrally located in the mesentery. It is worth noting that this pattern was not described in all reported cases of omental torsion documented by CT. In this occasion, it is difficult to separate omental torsion from other omental diseases, especially segmental omental infarction and primary epiploic appendagitis (4, 5).
As discussed above, torsion of the omentum is difficult to diagnose before surgery and is usually detected during laparotomy for acute abdominal pain. For the treatment of this condition, conservative approaches have been proposed, but there is a risk of abscess after omental necrosis, which can prolong the pain and hospital stay. Nonoperative management is preserved for patients who are hemodynamically stable and have radiological signs of torsion of the omentum in the preoperative period, unless acute abdomen exists (5, 6).
In this situation, the cardinal treatment remains the resection of the involved omentum, although the use of laparoscopy is becoming a highly valuable diagnostic and therapeutic tool nowadays.
Among the advantages of laparoscopy are the following: (A) it allows careful exploration of the whole abdominal cavity under visualization to confirm the diagnosis, (B) it facilitates aspiration and washing of the peritoneum and (C) it minimizes surgical aggression, postoperative pain, and complications related to the laparotomy wound (7, 8).
In conclusion, it is essential not to overlook this unusual entity among the differential diagnoses of acute abdomen. It is very important in early diagnosing patients with omental torsion and in differentiating surgical from nonsurgical conditions, thereby allowing the choice for conservative treatment when possible.

References
1. Theriot, J., Sayat, J., Franco, S., Buchino, J. - Childhood Obesity: A Risk Factor for Omental Torsion. Pediatrics., 2003, 112: 460.
2. Karayiannakis, A., Polychronidis, A., Chatzigianni, E., Simopoulos, C. - Primary torsion of the greater omentum: report of a case. Surg. Today, 2002, 32:913.
3. Feo, C., Porcu, A., Ginesu, G., Dettori, G. -Primary Torsion of the Greater Omentum: A Difficult Diagnosis. Dig. Dis. Sci., 2005, 50:1283.
4. Steinauer-Gebauer, A.M., Yee, J., Lutolf, M.E. - Torsion of the greater omentum with infarction: the vascular pedicle sign. Clin. Radiol., 2001, 56:999.
5. Caprino, P., Prete, F.P., Alfieri, S., Doglietto, G. - Acute abdomen for omental volvulus. Am. J. Surg., 2004, 187:268.
6. Naffaa, L.N., Shabb, N.S., Haddad, M.C. - CT findings of omental torsion and infarction: case and review of the literature. J. Clin. Imaging., 2003, 27:116.
7. Sanchez, J., Rosado, R., Ramirez, D., Medina, P., Mezquita, S., Gallardo, A. - Torsion of the greater omentum: Treatment by laparoscopy. Surg. Laparosc. Endosc. Percutan Tech., 2002, 12:443.
8. Siu, W.T., Law, B.K., Tang, C.N., Chau, C.H., Li, M.K. - Laparoscopic management of omental torsion secondary to an occult inguinal hernia. J. Laparoendosc. Adv. Surg. Tech. A, 2003, 13:199.


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