Pancreatic heterotopia presenting as a gastric submucosal lesion.

Editor

Heterotopia is the normal tissue of an organ found at an abnormal site without anatomic and vascular continuity from the original organ. It is thought that this arises during embryonic development, where groups of cells differentiate in a manner which is inappropriate for their anatomical position in the body1, 2. The usual gastrointestinal sites of Pancreatic Heterotopia (PH) include stomach, duodenum, jejunum, Meckels diverticulum, and gallbladder3. The condition is relatively infrequent and usually asymptomatic with post-mortem prevalences ranging from 0.6% to 13.7%4.

Rare symptomatic cases do arise causing dyspepsia, abdominal pain, melaena, anaemia, nausea and obstruction5, 6.

We report a case of PH presenting as intermittent gastric outlet obstruction. A 43 year old man presented with a 4 month history of intermittent post prandial epigastric pain and nausea. Complete gastric obstruction was not evident.

An upper gastrointestinal endoscopy revealed a 3cm lesion at the pylorus. (Fig 1) Ultrasound did not highlight any other cause for upper abdominal pain.

Fig 1

Gastroscopy view

Endoscopic ultrasound (EUS) of the lesion confirmed it to be situated within the submucosa having morophological characteristics suggestive of a gastro intestinal stromal tumour (GIST). (Fig 2) EUS can demonstrate echogenic differences between different types of submucosal lesions and the depth of its invasion. Characteristic EUS features highly suggestive of PH tissue are hypoechogenicity or heteroechogenic structure7. Anechoic areas usually correlate with ductal structures. These commonly arise from the third or fourth EUS layers of the GI tract or a combination of both.

Fig 2

Endoscopic ultrasound of gastric submucosal lesion

GIST also originate from the fourth layer of the GI tract and the presence of cystic spaces can indicate a risk of malignant change. The difficulty in diagnosis requires histological confirmation for a definitive answer.

CT scan confirmed the endoscopic ultrasound findings. There was no eveidence of distant metastatic spread. (Fig 3) Retrospective study of CT appearances of gastric submucosal lesions shows that by using a list of specific CT criteria PH can be differentiated from small gastro intestinal stromal tumours or leiomyoma with a high degree of accuracy8.

Fig 3

CT scan axial view. Red arrow: gastric submucosal lesion

Subsequently the patient proceeded to laparotomy where a 3cm lesion was located in the pyloric channel. A distal gastrectomy was undertaken and the patient made an uneventful recovery. Review in the outpatient department several months following surgery confirmed the relief of his symptoms. Histology revealed the lesion to be consistent with a focus of PH encompassing a cystically dilated duct. (Fig 4)

Fig 4

Pancreatic exocrine glands

Comment

PH is part of the differential diagnosis of gastric submucosal nodules. The likely aetiology of PH is congenital and usually asymptomatic. However if symptoms occur they are usually in the fourth and fifth decades5. PH is a rare differential diagnosis of a submucosal gastric lesion.

The distribution of PH is 25% in the stomach and 30% in the duodenum9 with the rest distributed at other sites throughout the gastrointestinal tract. There is also the exceedingly rare possibility of malignant change10, 11.

This case highlights the rare aetiology of a symptomatic gastric submucosal lesion as well as the difficulty in making a preoperative diagnosis even with modern imaging modalities such as CT and EUS.