Introduction

Torsion of the greater omentum is an uncommon cause of acute abdominal pain that mainly affects adults in their fourth or fifth decade. The clinical features are not specific for this condition and often resemble acute appendicitis or acute cholecystitis. The diagnosis is usually made at laparotomy. We report two cases of primary omental torsion, followed by a review of the diagnostic and therapeutic implications of this condition.

Case 1

A 30-year-old male athlete was admitted in our department with a 7-day history of right-sided, abdominal pain that was not associated with fever, anorexia or vomiting. The pain had started as nonspecific abdominal disturbance and was increasing in severity. Two days before, he was admitted for the first time due to severe abdominal pain that was increasing in standing position and relieved in supine position. At that time, the pain was attributed to abdominal wall trauma and possible subsequent hematoma, due to previous heavy abdominal muscle exercise. He was discharged with instructions for resting and prescription for NSAIDs, which resulted in transient remission of his symptoms. On the day of his second admission, the pain was extremely severe (the patient reported transient loss of consciousness) and was not affected by his body position. On physical examination, the patient had tenderness, guarding and rebound tenderness in the right side of his abdomen, but no mass was palpable. Laboratory findings were within normal ranges, except for mild leukocytosis (12500/mm ³ ). Due to the inconsistency between clinical presentation and laboratory findings, an ultrasound examination was performed, which showed an encysted infusion in the right abdomen, beneath the rectus abdominis fascia (figure 1). A laparotomy was performed, through a right paramedian incision. A small amount of serosanguinous fluid was found, in association with a large (10cm x 6cm x 1.5cm) tongue-like projection originating from the greater omentum, which was twisted several times (figure 2). The mass was excised and an appendectomy was also performed. No other intra-abdominal pathology was found. Histological examination of the omental segment showed focal hemorrhage, vascular congestion and nonspecific inflammatory infiltration. The patient recovered uneventfully and was discharged on the fourth postoperative day.

Case 2

A 43-year-old female was admitted in our department with a 4-day history of nonspecific abdominal pain. The pain was more severe in the right subcostal area and was associated with fever (37.7 ^o C). The patient reported deterioration of symptoms in standing position and with coughing, and remission in supine position. Her past medical history was unremarkable. On physical examination, the patient had tenderness, guarding and rebound tenderness in the right subcostal area, associated with decreased bowel sounds. Laboratory findings were normal except for leukocytosis (13.700/mm ³ ). The working diagnosis was acute cholecystitis, so an ultrasound examination was carried out, which showed a hyperechoic soft tissue mass (5 x 6cm) lying beside the normal, stone-free gallbladder. A diagnostic laparoscopy was performed using 3 trocars (umbilical, subxiphoid and right upper quadrant). The abdominal exploration revealed a tongue-like projection of the greater omentum which was twisted around its long axis leading to infarction. Additional findings were the presence of a small amount of serosanguinous fluid in the right paracolic gutter, along with a normal appendix. The twisted part of the omentum was resected using bipolar forceps and removed through the subxiphoid trocar. Histological examination showed vascular congestion and necrosis of the omental segment. The patient recovered uneventfully and was discharged on the third postoperative day.

Figure 1

Figure 1: Encysted infusion beneath the rectus abdominis fascia (arrows)

Discussion

Omental torsion is a rare cause of acute abdomen that was first described by Eitel in 1899 (₁) . Today, more than 300 cases of this condition have been described in the published literature. It usually affects adults between 30 to 50 years (₂) and children between 9 to 16 years of age (₃) . The male to female ratio is approximately 1.5 : 1 (₄) .

Omental torsion occurs when omentum twists around its long axis, causing venus obstruction, edema and vascular compromise (₃) . It can be primary (idiopathic) or secondary (₅) . Primary omental torsion, which counts for one third of cases (₆) , is due to a rotation of a mobile omentum segment around a pivotal point (₇) . The etiology of this primary form still remains unclear but several factors have been implicated in its pathogenesis (₈) . Predisposing factors of primary torsion include anatomical malformations of the omentum such as bifid omentum or tongue-like projections, local variations in omental fat distribution as in obesity and vascular abnormalities of the omentum (₃,₆,₉,₁₀) . Precipitating factors include trauma, hyperperistalsis due to heavy meals and increased intra-abdominal pressure resulting from exercise or coughing (₃,₆,₁₁,₁₂) . Primary omental torsions are usually located in the right side of the abdomen. In approximately 90% of cases the omentum is found twisted around the distal right epiploic artery, which is due to the fact that the right side of the omentum is longer and thus more mobile than the left side (₁₃,₁₄) . The secondary form is more common (₆) and it occurs when the free omental end is attached to a pathologic intra-abdominal process (₁₅) . Lesions associated with secondary omental torsion may be omental (tumors, cysts) (₁₆,₁₇) , parietal (inguinal hernias, adhesions) (₁₈,₁₉) or visceral (appendicitis, cholecystitis) (₂₀,₂₁) .

The clinical presentation of omental torsion is nonspecific and largely depends on the degree and duration of torsion. The cardinal feature of omental torsion is abdominal pain of sudden onset and short duration, which is constant, non-radiating and gradually increasing in severity. The pain is usually located in the right side of the abdomen with occasional prior acute presentations of nonspecific pain, suggestive of recurrent torsion (₂₂) . Another feature that we observed in both our cases is the increasing of pain in standing position and remission in supine position, at least in the early stages. Anorexia, nausea and vomiting are present in less than 50% of cases, associated at variable extents, with mild fever, bowel disorders, dysuria and leukocytosis (₁₂) . The physical examination reveals right lower quadrant tenderness, which is frequently accompanied by guarding and rebound tenderness. If the involved segment of the omentum is sufficiently large, a mass may be palpable in up to one third of patients (₁₂,₂₃,₂₄,₂₅) .

Imaging evaluation of primary omental torsion includes ultrasonography and computer tomography, as plain films are of little diagnostic help. The cardinal findings on ultrasound examination are an ovoid hyperechoic soft-tissue mass adhering to the anterior abdominal wall with hypoechoic rim and non-compressibility of the fat (₂,₃,₂₆) . According to our experience, ultrasound scans were suggestive of intra-abdominal pathology but their diagnostic specificity was low. The typical CT findings include a streaking or “whirling pattern” of inflammatory tissue, potentially with a fluid cavity based on the degree of necrosis present (₂₇) . A basic advantage of CT versus an ultrasound scan is the reliability of identifying the mass in the characteristic location between the anterior abdominal wall and the colon (₂₆) . Preoperative differential diagnosis should include all disorders which give rise to acute abdominal pain in the right side of the abdomen, such as cholecystitis, appendicitis, perforated peptic ulcer, intestinal obstruction, Meckel's diverticulum, abdominal wall hematoma, mesenteric adenitis, torsion of accesory spleen, ovarian cyst torsion, ectopic pregnancy and salpingitis.

Figure 2

Figure 2: Schematic representation of twisted tongue-like projection of the greater omentum

Physical findings and laboratory examinations are usually not sufficient to establish a preoperative diagnosis of omental torsion, so most of the patients are submitted to laparotomy for “acute appendicitis” or acute abdomen of poorly defined origin. The intraoperative findings that should raise the suspicion for omental torsion are the presence of free serosanguinous fluid along with the absence of other intra-abdominal pathology (normal appendix, absence of Meckel's diverticulum) (₁₅,₂₈) . Although there are reports that support the conservative treatment of omental torsion (₂₉) , most authors agree, that treatment of choice is resection of the involved segment of the omentum along with appendicectomy, for the prevention of future differential diagnostic problems (₂,₉,₃₀,₃₁,₃₂) . Excision of the twisted part of the omentum offers immediate relief of symptoms and reduction of the possibility of complications such as adhesions, bowel obstruction and abscess formation (₁₂,₂₃,₂₄,₃₃,₃₄) . More recently laparoscopic treatment is reported to be an ideal approach in the management of primary omental torsion. We agree that laparoscopy is a useful method for both diagnostic and therapeutic purposes (resection of affected omentum) (₃₀,₃₅,₃₆,₃₇) .

Conclusion

Primary omental torsion is a rare cause of acute abdomen, which affects both children and adults. The clinical presentation, laboratory findings and imaging evaluation are often non-specific. The differential diagnosis includes appendicitis, cholecystitis, Meckel's diverticulum, twisted ovarian cyst, abdominal wall hematoma and a variety of other entities. The diagnosis is usually made at laparotomy. Nowadays, laparoscopic approach seems to be the most safe and effective tool for diagnosis and final treatment.

Correspondence to

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