Non-Mass Forming Isolated Omental Panniculitis : A Case Report

A 61-year-old man presenting with abdominal pain and fever refractory to antibiotics underwent diagnostic laparoscopy and non-mass-forming isolated omental panniculitis was identified. He presented with left-upper-quadrant abdominal pain. Laboratory data and the CT findings suggested intraabdominal bacterial disease in the splenic flexure, which we treated with antibiotics and fasting. He clinically improved once, but later relapsed with abdominal pain migration to the left-lower-quadrant. CT re-examination revealed no inflammation in the splenic flexure, but attenuation of adipose tissue in the greater omentum. We partially extracted the greater omentum during diagnostic laparoscopy and diagnosed omental panniculitis and administered steroids. He improved and was discharged three days after starting oral prednisone and is recurrence-free with a close follow-up. The characteristic CT feature of omentum panniculitis is a high-density fatty mass, but we noted only an attenuation of adipose tissue in the greater omentum. Diagnositic laparoscopy is useful for diagnosing this condition.


Introduction
Isolated omental panniculitis is a rare form of intraabdominal panniculitis, mainly involving the mesenteric adipose tissue of the small intestine or colon [1] [2].The characteristic computed tomography (CT) features of intraabdominal panniculitis described in previous reports have ranged from increased attenuation to a solid soft tissue mass.In contrast, the only CT finding described for How to cite this paper: Hakoda, K., Yoshimitsu, M., Omori, I., Miguchi, M., Kohashi, T., Ohdan, H. and Hirabayashi, N. We herein report a case of isolated omental panniculitis that showed only attenuation of the adipose tissue of the greater omentum.Exploratory laparoscopy proved to be useful in diagnosing this condition.

Case Report
A 61-year-old man presented with a 1-week history of intermittent left upper quadrant abdominal pain and a fever (38.3˚C).His medical history and family history were unremarkable.Laboratory tests revealed an elevated white blood cell count (19200/mm 3 ; reference, 4000 -9000/μL) and increased levels of Creactive protein (CRP, 24.8 mg/dL; reference, 0.3 -0.0 mg/dL) and procalcitonin (PCT, 1.05 ng/ml; reference, 0.49 -0.00 ng/mL).CT revealed attenuation of the adipose tissue in the splenic flexure and wall-thickening of the nearby transverse colon.A large amount of ascites from the surface of the liver to the pelvis was noted in the left thoracic cavity, along with plural effusion suggesting involvement in the inflammation.There was no free air (Figure 1).We started treatment with antibiotics (PIPC/TAZ 4.5 g, every 8 h), fasting and fluid therapy under a diagnosis of bacterial intraabdominal inflammation.The clinical data improved once, but six days after admission, the patient's condition became exacerbated, and the abdominal pain migrated to the left lower quadrant.
CT re-examination revealed no attenuation of adipose tissue in the splenic flexure and also decreased ascites and pleural effusion; however, attenuation of the adipose tissue of the greater omentum was noted, suggesting inflammation of the greater omentum.This prompted us to consider a diagnosis of omental panniculitis (Figure 2).infiltration of numerous inflammatory cells, immature fibroblasts, fatty necrosis and fibrosis, findings consistent with omental panniculitis without malignancy (Figure 3).
The patient was started on prednisone 20 mg (intravenous) daily.His symptoms gradually ameliorated, and he was able to eat without nausea.He was discharged 3 days after starting oral prednisone (20 mg) and has been closely followed-up without recurrence.

Discussion
Isolated omental panniculitis is a rare form of intraabdominal panniculitis, mainly involving the mesenteric adipose tissue of the small intestine or colon [1] [2].

Conclusion
In conclusion, isolated omental panniculitis can present as only the attenuation of adipose tissue of the greater omentum without any findings of a high-density fatty mass, and exploratory laparoscopy can be useful for the diagnosis of this condition.We must be aware that isolated omental panniculitis can manifest with CT findings other than those expected.Some cases of isolated omental panniculitis may remain unrecognized, and thus there may be hidden cases of isolated omental panniculitis treated with only antibiotics or fasting under a misdiagnosis as another intraabdominal inflammation disease.Dignostic laparoscopy can definitively exclude other abdominal inflammatory diseases, and a surgical biopsy of the greater omentum is less invasive than laparotomy.When encountering patients with abdominal pain refractory to antibiotics, omental panniculitis should be considered as a differential diagnosis, and diagnostic laparoscopy may need to be performed.
Figure 1.Enhanced CT revealed attenuation of the adipose tissue in the splenic flexure (dotted line area) and wall thickening of the nearby transverse colon (orange arrow).

Figure 2 .
Figure 2. At the sixth hospital day, enhanced CT re-examination revealed no attenuation of the adipose tissue in the splenic flexure (dotted line area) and decreased ascites and pleural effusion (orange arrow) (a, b); however, attenuation of the adipose tissue of the greater omentum was noted (c: encircled region).

Figure 3 .
Figure 3. On hematoxylin-eosin staining, acute inflammation was observed with infiltration of numerous inflammatory cells, immature fibroblasts, fatty necrosis and fibrosis of the fat tissue.