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Gastric Adenomyosis: A Rare Cause of Pyloric Mass in Children

Adenomyoma of the stomach is a benign tumor with a very low incidence. Clinical presentation and imaging modalities are usually nonspecific and variable. A rare case of gastric adenomyoma in a 12‐year‐old child is being reported who presented with gastric outlet obstruction. The diagnosis could only be established after an excision biopsy performed after multiple diagnostic modalities failed to clinch the diagnosis. The case is being reported in view of the rarity of this entity in the pediatric age group as a cause of gastric outlet obstruction.

contrast-enhanced computed tomography (CECT) scan of abdomen confirmed the presence of a heterogeneously enhancing mass in the anteroinferior wall of the gastric antrum causing luminal obstruction [ Figure 1a]. This mass also showed focal fluorodeoxyglucose (FDG) uptake [ Figure  1b] on positron emission tomography (PET scan). Investigations were done to rule out tuberculosis and lymphoma as a possible cause of distal gastric and pyloric thickening.
With a working diagnosis of gastrointestinal stromal tumor (GIST), an exploratory laparotomy was planned. A circumferentially thickened and bulky pylorus was found with normal duodenum and proximal stomach.

Introduction
G astric adenomyoma is a rare tumor with a benign course. Children may present with nonspecific symptoms but can also exhibit urgencies such as melena and gastric outlet obstruction (GOO). Surgical resection is the cornerstone in its treatment. Histologically, it is composed of epithelial elements surrounded by a smooth stroma. Herein, we present a rare case of gastric adenomyoma in a 12-year-old child to highlight the diagnostic dilemma and the importance of surgical resection and histopathology in management.

Case Report
A 12-year-old boy presented with complaints of episodic, dull-aching pain in the left upper abdomen for the past 1 month. There was associated history of episodes of nonbilious vomiting with the pain. The child underwent upper gastrointestinal endoscopy elsewhere, where a submucosal bulge in the pyloric region was documented, and an endoscopic biopsy from the site of the bulge was suggestive of a spindle cell neoplasm. He was referred to our center for further management.
On presentation, his general condition was well preserved. On examining the abdomen, no lump or organomegaly was found. Ultrasonography (USG) of the abdomen revealed circumferential thickening in the distal body of the stomach. Subsequently, a The patient was asymptomatic after a year of follow-up and a PET scan done (3 months after resection) did not reveal any FDG uptake. Serial long-term follow-up with USG has been planned to rule out local recurrences if any.

Discussion
Gastric adenomyoma, also known as adenomyosis and myoepithelial hamartoma is a rare benign entity. Only 52 cases were reported in the literature till 2017.
Although the age at presentation may vary, most cases present between fourth to sixth decades of life. The youngest case described in literature is a 1-week-old neonate. [1] No gender preponderance has been seen for this tumor. [2] These tumors most commonly involve the antrum (85%) and pyloric (15%) regions of the stomach. [3] The etiopathogenesis of gastric adenomyoma is a gray zone, and there are two schools of thought. While the majority consider its occurrence as a developmental aberration, there is considerable evidence of it being an abortive variant of heterotopic pancreas. The presence of epithelial and smooth muscle components supports the former ideology and coexistence with heterotopic pancreas and histology justifies the latter. It can also present with other conditions such as gastric duplication, annular pancreas, and duodenal adenomas. [2] Children with gastric adenomyoma usually present with nonspecific clinical features such as episodic pain, nausea, vomiting, and melena. There are some reports of intermittent pyloric obstruction in patients with gastric adenomyoma as well. [3] Imaging techniques such as USG and CECT of the abdomen are usually noncontributory, and the diagnosis of gastric adenomyoma is made only by histopathology in majority of the cases. Similarly, investigations such as UGI contrast series and endoscopy cannot differentiate between conditions such as gastric adenomyoma, GIST, leiomyoma, lymphoma, and lipoma and carcinoid tumor. [3,4] Thus, it is not uncommon to misdiagnose it as some other pathology. In our case also, these investigations did not lead to a diagnosis. One peculiar finding was the focal FDG uptake by the thickened pylorus which has not been described previously in gastric adenomyoma. The mechanism behind this uptake is a matter of speculation since a benign process like adenomyomas is unlikely to be FDG avid. Despite this biological behavior, a repeat PET scan was performed, and it did not show any FDG uptake.
The management consists of surgical resection of the tumor, and postoperative histopathology is recommended for making a correct diagnosis. [5] While resection of the tumor with an adequate margin is indicated in most of the cases, limited resection should be preferred in tumors with involvement of the periampullary region. In these cases, a frozen section can aid in making a preemptive diagnosis and can avoid the morbidity of a more radical surgery. [3] Endoscopic submucosal resection is also a feasible treatment modality in adults as reported by Wang et al. in their series of 15 cases of gastric adenomyoma. [1] The risk of malignant transformation is rare (<2%) and is similar to that of hamartomatous polyps. Histopathology plays a vital role in making a diagnosis of gastric adenomyoma. On gross examination, the mass arises in the submucosa and protrudes into the lumen of the stomach. Microscopically, the tumor shows the presence of epithelial component (tubules, Brunner's glands, and Pancreatic acini) surrounded by smooth muscle stroma. [6] Conclusion A gastric adenoma is a rare cause of pediatric GOO. Endoscopic biopsy may miss the diagnosis, and therefore, complete surgical resection should be attempted after ruling out other common causes of GOO. The presence of characteristic histopathological findings should confirm the diagnosis.

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The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/ her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest
There are no conflicts of interest.