Pancreaticoduodenectomy for pancreas carcinoma occurring in the annular pancreas: report of a case

The annular pancreas is a rare anatomical anomaly, in which the pancreas parenchyma surrounds the descending part of the duodenum. Most of adult cases become symptomatic at ages between 30 and 50 years [5], and males occupied 65.1 % of total cases [6]. The predominant symptoms of the annular pancreas are epigastric pain, postprandial fullness, vomiting, and weight loss in adults [7, 8]. Furthermore, the main complications of the annular pancreas are peptic ulcers, cholecystolithiasis and pancreatitis [9].

Previously, two hypotheses have been proposed to explain the etiology of the annular pancreas: Lecco’s theory attributes it to adhesion of the right ventral angle to the duodenal wall [10], and Baldwin’s theory considers it to involve persistence of the left ventral bud [11]. Although Lecco’s theory is supported by many reports, not all cases can be explained by only this hypothesis.

The presence of the annular pancreas was reported in three of 20,000 autopsies [3] and three of 24,519 surgical cases [4]. Although the annular pancreas is rare, it has been recently recognized frequently due to progression of diagnostic imaging devices. Among patients undergoing endoscopic retrograde cholangiopancreatography (ERCP), approximately one in 1000 examined cases was found to have the annular pancreas [3, 12]. In these cases, ERCP may not always be successful, due to technical difficulty in some cases, particularly in cases with the duodenal ulcer and/or stenosis of the descending part of the duodenum [13]. In most cases, multi-slice CT shows the circumferential pancreatic parenchyma around the descending part of the duodenum [13, 14]; however, in some cases, this imaging method may lead to misinterpretation as a thickening of the duodenum [15]. With this in mind, magnetic resonance imaging (MRI) and MRCP are useful for understanding anomalies observed in the pancreatic anatomy [13, 15, 16].

The efficacy of endoscopic ultrasonography in the annular pancreas has also been reported, as for less-invasive imaging devices [16, 17]. In addition, EUS-FNA is a highly accurate method for the histological diagnosis of pancreatic carcinoma [18, 19]. In the present case, a definitive diagnosis was possible without operation by EUS-FNA.

Yogi et al. classified six variants of the ductal anatomy in patients with annular pancreas [9]. The most frequent type is type I, in which the main pancreatic duct (MPD) in the annular pancreas opens into the duct of Wirsung. In the second most frequent type, the MPD is encircled the duodenum (type II). The other four types of anomaly are uncommon. The present case is presumed to be type IV, in which the MPD in the annular pancreas opens into the CBD without the duct of Wirsung.

Among the cases reported in the literature, only five have been reported to involve the annular pancreas [12, 15, 20‐22]. Among them, three cases were located in the pancreas head, one case in the pancreas body, and one case existed diffusely in the pancreas; however, there were no cases with existing carcinoma in the annular pancreas, except the present case.

In conclusion, to our knowledge, the present report is the first clinical case of pancreatic carcinoma occurring from the annular pancreas. In patients with the annular pancreas, the possibility of coexistent malignancy in the pancreato-biliary system should be considered. EUS-FNA is most likely effective for the definitive diagnosis of pancreatic carcinoma occurring in the annular pancreas. For further elucidation of the annular pancreas, MRCP and the resected specimen cholangiopancreatography would be beneficial.