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On opening the surgical specimen, the center portion of the lobulated nodule showed the presence of umbilication. Light microscopy showed that the lesion was located in the submucosa of the ileum and was composed of pancreatic acinar cells, pancreatic ducts, and islets of Langerhans (Figure 1 and Figure 2). No malignant transformation was found. The mucosal and serosal surfaces of the ileum were normal. The pathological diagnosis was heterotopic (ectopic) pancreas of the ileum.

Heterotopic, ectopic, or aberrant pancreatic tissue, also known as a pancreatic rest, is an uncommon congenital anomaly defined as extra pancreatic tissue located far from the pancreas and without connection via vascular or anatomical means to it.¹ Several theories have been advanced to explain the pathogenesis and occurrence of heterotopic pancreas. The most tenable and plausible implicates migration and/or rests of branching pancreatic tissue buds from the developing pancreas during embryogenesis.² The first reported case of heterotopic pancreatic tissues was described in 1729, but it was not until 1859 that histological confirmation was provided by Klob.³ Heterotopic pancreatic tissues have been reported to occur throughout the digestive tract, the most frequent site being the upper gut, including the stomach, duodenum, and jejunum.⁴ Uncommon locations are the colon, spleen, liver, biliary tract, mesentery, and lymph nodes.^1,4 Heterotopic pancreas found in the ileum is rare.

Pathologically, a mass of heterotopic pancreas generally ranges from 0.2 to 3.0 cm in its greatest dimension (average size, 1.1 cm) and usually presents as a well-circumscribed, soft, rubbery, yellow, submucosal or intramural mass.^2,5 Some demonstrate central umbilication or ulceration on radiographic contrast studies. Histologically, herotopic pancreas has been divided into 4 types²: type I is total pancreatic heterotopia, which is composed of all pancreatic cell types; type II contains pancreatic ducts only; type III is composed of acinar cells only; and type IV is composed of islet cells only. Our case is an example of type I and had all of the histological characteristics of the pancreas, including acinar cells, islets of Langerhans, and pancreatic ducts. This is typical of extra pancreatic tissue.

Most patients with heterotopic pancreas are free of symptoms and a diagnosis before surgery is difficult. Such cases are usually discovered during radiographic or endoscopic examination of the gut, or during surgical exploration for other disease. Although the most common symptoms attributed to heterotopic pancreas, such as abdominal pain, nausea, vomiting, anemia, weight loss, and melena, are present at the time of diagnosis,⁶ this lesion has no specific clinical features. Endoscopic ultrasonography often shows a submucosal bulge covered by normal mucosa with or without central umbilication.^1,7 Endoscopic ultrasonography seems to be a reliable method for providing the precise localization, extent, and characteristics of the submucosal mass, allowing one to differentiate it from all other types of masses such as tumors. However, the final diagnosis of pancreatic heterotopia is often reached by histological examination of surgical specimens.

The complications of heterotopic pancreas usually include inflammation with formation of an inflammatory mass, ulceration, bleeding and obstruction, and pancreatitis.⁵ Malignant transformation is possible and carcinoma of the heterotopic pancreas has been reported.^2,8- 9 The 3 criteria for a carcinoma arising from heterotopic pancreatic tissue that have been reported by Makhlouf et al⁴ may prevent its misinterpretation as a metastatic tumor.

Armstrong et al¹⁰ reported that differentiation from a leiomyoma or an adenomatous polyp is sometimes difficult; in addition, when the central umbilication is larger than usual, heterotopic pancreas may be confused with the base of a gastric or duodenal peptic ulcer. The leiomyoma produces a smooth elevation in the mucosa and may have central umbilication, but radiography will not show the presence of ducts. A small nodule of heterotopic pancreas cannot be distinguished easily from an adenomatous or regenerative polyp, but a polyp is usually larger and does not show central umbilication.

The management of heterotopic pancreatic tissues is somewhat controversial. Endoscopic removal is at risk of perforation or bleeding because the lesion is submucosal. Operative treatment is considered not only for complicated cases, such as bleeding, obstruction, and malignant transformation, but also for a definitive diagnosis to exclude a neoplastic lesion in symptomatic patients. Furthermore, our opinion is that when heterotopic pancreas is found incidentally, it is advisable to resect it intraoperatively to avoid late complications and a second operation, as well as to avoid the risk of malignant transformation.

In conclusion, we describe a 2.0-cm-diameter mass of heterotopic pancreas involving the ileum in a 62-year-old man. This patient was asymptomatic, and the lesion was found incidentally during emergency surgery. All histological features of the pancreas were seen in the surgical specimen. We recommend that heterotopic pancreas be treated with surgical excision, especially when it is found incidentally during an abdominal operation, to avoid late complications and malignant transformation.

Correspondence: Bo-Guang Fan, MD, PhD, Department of Surgery, Taizhou Hospital, Taizhou Linhai, Zhejiang Province, China (fanboguang@gmail.com).

Accepted for Publication: April 8, 2005.

Acknowledgment: We thank Shuangqi Yang, CPM, for kind technical support during preparation of the illustration.