Various diseases present as acute right abdominal pain in adults. The most common differential diagnoses are, for example, acute appendicitis, acute cholecystitis, and diverticulitis [1]. However, when there is a lack of gastrointestinal symptoms, such as nausea, vomiting, or diarrhea, it is difficult to make a diagnosis. Omental torsion is a rare cause of abdominal pain that presents with non-specific symptoms and signs [2]. This condition occurs when the greater omentum twists along its long axis, and the vascular perfusion is compromised, which leads to infarction and necrosis [2]. The diagnosis is challenging without imaging studies since the symptoms mimic other causes of acute abdomen, while the treatment is simple surgical excision of the affected omentum [3],[4].

A 55-year-old woman visited a gastroenterologist at a nearby clinic due to right abdominal pain for 4 days. Esomeprazole was prescribed, and an abdominal ultrasound was planned on the next day. She revisited the clinic on the schedule; however, she collapsed while waiting for the ultrasound. The doctor referred her to our hospital, suspecting shock caused by peritonitis with an undiagnosed condition.

Presenting at our hospital, she was alert. She complained of right abdominal pain and general weakness. The abdominal pain was located in the right part; it was constant and non-radiating. It worsened over the last four days and was not associated with nausea, vomiting, and diarrhea. Detailed history taking revealed that she had experienced similar mild to moderate right abdominal pain several times in the past. The first episode occurred while she was pregnant at age 26. The pain subsided spontaneously every time; therefore, she had not sought medical advice. She had no history of hospital admission except for the delivery and had no history of operation.

Physical examination showed she was not in shock: heart rate 86 beats per minute, blood pressure 162/100 mmHg, oxygen saturation 96% at ambient air, and body temperature 37.7°C. Abdominal examination revealed rebound tenderness in the right side, and rigidity was localized at the right lower quadrant. Carnett sign was positive. She had a mildly elevated C-reactive protein level of 6.6 mg/dL (reference range, 0.0–0.3 mg/dL); otherwise, laboratory findings were unremarkable (Table 1). An emergency physician suspected cholecystitis with peritonitis, and a computed tomography (CT) scan was performed (Figure 1A and Figure 1B).

The CT scan showed a normal gallbladder. However, density of intra-abdominal fat on the right side was markedly increased, indicating inflammation of the greater omentum. The radiologist additionally pointed out the whirl sign in the right distal greater omentum between the ascending colon and the transverse colon. Thus, the diagnosis of omental torsion was made. Necrosis of the affected omentum was suspected as indicated by the hyper-attenuating fat around the whirl sign in the CT scan. Therefore, emergency laparoscopy was performed; it revealed the necrotic omentum with adherence of the greater omentum to the anterior abdominal wall. Omentectomy was performed (Figure 2A and Figure 2B). The confirmed diagnosis was omental torsion with necrosis, and the histological findings revealed no malignancy. The patient was discharged six days after the operation without any complications.

Omental torsion is rarely suspected prior to an imaging study because the clinical symptoms and signs are thought to be non-specific [2]. However, detailed history taking and physical examination help find the specific points that can help to make a provisional diagnosis. Without a provisional diagnosis in mind, it is likely that the characteristic sign in the CT scan can be missed by non-radiologists, and the evaluation of the image findings can become very challenging.

The interesting characteristics of omental torsion is the lack of gastrointestinal symptoms [5]. In most cases, omental torsion is often misdiagnosed as appendicitis, diverticulitis, or cholecystitis because the right-sided abdominal pain is a common complaint in all of them [2]. Omental torsion has a wide variety of differential diagnosis (Table 2) since the main symptom is non-specific persistent abdominal pain [6]. Meanwhile, an important characteristic of omental torsion is the absence of gastrointestinal symptoms, such as nausea, vomiting, diarrhea, and constipation [7]. When these symptoms are absent in patients with abdominal pain, it would be worth considering non-gastrointestinal diseases [8]. In our case, the patient did not have gastrointestinal symptoms; she was complaining of a constant non-radiating pain in the right side of the abdomen.

Another interesting characteristic of our patient is positive Carnett sign that indicated an abdominal wall pathology for the cause of the pain [8]. Briefly, Carnett test is a maneuver to examine the change of abdominal tenderness while a patient tenses the abdominal muscles by lifting the head and shoulders. If the pain increases, it implies the abdominal wall pain. On the other hand, if the pain does not change or subsides, it implies intra-abdominal pain [8]. Although omental torsion generally does not cause abdominal wall pain, our patient showed positive Carnett sign. The adhesion of the torsed omentum to the anterior abdominal wall was thought to be the reason of positive Carnett sign. The patient started having abdominal pain during her first pregnancy. Afterward, she had several episodes of similar pain. Probably, these pain episodes were due to the omentum recurrently torsed and gradually adhered to the abdominal wall.

Omental torsion occurs more frequently in adults of 30 to 50 years, and males are affected twice as females [6],[9],[10]. Some cases have been reported from children [2],[6]. Constant non-radiating pain, which increases in severity over time, is the earliest symptom of omental torsion. The pain is commonly located in the right lower quadrant. Most cases have single episodes of pain, while recurrent torsions cause repeated pain. About 50% of patients may have a low-grade fever and moderate leukocytosis [6]. Computed tomography scan provides the definitive diagnosis of omental torsion. The classical signs are the whirl sign of a fatty mass and concentric linear stands in the greater omentum [3],[4]. Abdominal ultrasound is helpful however less sensitive than CT scan due to its operator-dependent nature. A complex mass with hypoechoic and solid zones attached to the peritoneum can be seen in the ultrasound [6],[9].

Omental torsion can be divided into primary when the cause is unknown and secondary when it is associated with an intra-abdominal pathology. Salient characteristics and associated risk factors of primary and secondary omental torsions are presented in Table 3 [5]. Clinically, symptoms and signs are similar in both types of torsions. A condition with a similar presentation but different pathology is omental infarction without torsion. The cause of omental infarction is thrombosis, vasculitis, or right-sided heart failure leading to mesenteric venous congestion [11]. To differentiate omental infarction from omental torsion by imaging studies is sometimes challenging, especially when the whirl sign of the vessels is unclear. Considering the patient's condition and past medical history would help to make the diagnosis. The treatment is usually surgical resection of the necrotic omentum in either case [12].

Surgical resection of the affected omentum is the common management. As laparoscopic resection has the advantages of minimally invasive surgery, it should be considered as the treatment of the benign disease [13]. On the other hand, CT scan is being used widely, and when a pre-operative diagnosis is possible, conservative management has been proposed in the patients without complications [14],[15]. The conservative management includes analgesics and prophylactic antibiotics, along with careful imaging follow-ups to rule out other acute abdominal pathologies. However, these patients may need prolonged analgesics and may develop complications, such as abscess formation and adhesions [6].

Omental torsion is an uncommon abdominal disease. Although it is often described as abdominal pain with non-specific symptoms, the lack of gastrointestinal symptoms is an important characteristic. Carnett test can be positive in a case of omental torsion adhered to the anterior abdominal wall. These clinical signs are helpful to evaluate the imaging studies and make the diagnosis.