Case Report and Review of the Literature Gastric Adenomyoma: A Case Report and Comprehensive Review of the Modern Literature

clarity. We present an updated review of the modern literature and a case of gastric adenomyoma, as well as define an algorithm using histology and immunohistochemical (IHC) stains (desmin, CKIT, DOG1, PDGF and CK7) for the diagnosis of gastric adenomyoma in a noninvasive manner in order to potentially avoid unnecessary surgery.


Introduction
Gastric adenomyoma is a rare, benign lesion composed of epithelial and spindle cells with 85% of lesions occur in the antrum of the stomach and 15% occur in the pylorus [1]. They most often occur in adults, although there are rare case reports of these lesions in children [2]. The majority of gastric adenomyomas are an incidental/asymptomatic finding in patients being evaluated for nonspecific gastrointestinal symptoms [3,4]. Rarely, they present with melena and in children, some cases reportedly mimicked gastric duplication cysts, pyloric stenosis, or caused gastric outlet obstruction [1, [5][6][7][8][9][10].
Originally described by Magnus-Alsleben in 1903, there have been 61 cases identified since that time to present [11]. Diagnosis of this lesion is exclusively by histology [11]. However, the spindle cell component and the rarity of this lesion often have clinicians confusing this benign tumor for a gastrointestinal stromal tumor (GIST). Further complicating management is that most of the case reports suggest that resection is the only method to confirm the diagnosis. We present our experience with such a case and review the modern literature (since 2017 as these were the only ones with complete pathology and IHC information for comparison). More importantly, however, we propose new noninvasive histology and IHC based algorithm to define gastric adenomyoma and avoid unnecessary surgery.

Case Report
We present a case of a 56-year-old African American female who presented to her gastroenterologist for worsening intermittent upper abdominal pain and dyspepsia refractory to famotidine. She had no nausea, vomiting, recent weight change or early satiety. Her reflux symptoms occurred on most days. Gastroenterology (GI) ordered a CT

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of her abdomen and pelvis and performed an EGD and EUS. The CT demonstrated a 33 x 23 x 27 mm mixed attenuation exophytic mass associated with the gastric antrum and a central area of necrosis ( Figure  1). An EGD demonstrated a normal esophagus and stomach except for a submucosal mass (mural-based lesion) in the antrum ( Figure 2). A subsequent EUS was performed and noted an 8mm x12mm lesion arising from the 4th layer of the antral wall that was mural in nature, not luminal and most consistent with a leiomyoma or GIST. FNA demonstrated a few scattered spindle cells and pathology favoured a leiomyoma vs. GIST with the specimen diffusely positive for desmin while negative for CD34 and CD117. No additional stains were performed.  Note that there is no bleeding or obstruction.
The patient was referred to surgical oncology due to concern for a leiomyosarcoma (not a GIST because of the lack of CD117 staining) and given the rarity of a leiomyoma in the antrum of the stomach. Just over 1 month after her initial presentation, the patient underwent a robotic resection of the antral mass via partial gastrectomy. Postoperative histological evaluation of the lesion revealed a benign tumor composed of haphazard foci of dilated ducts lined by foveolar type epithelium with subepithelial glands supported by scant loose connective tissue with sparse mixed inflammation embedded within dense smooth muscle, with no interstitial metaplasia or dysplasia ( Figure 3). The tissue stained positive for desmin and negative for CD34 and CD117. Diagnosis of gastric adenomyoma was made without additional stains based on the epithelial cells in concert with the spindle cells in this lesion. Two weeks postoperatively, the patient was recovering well.

Discussion
Gastric adenomyoma is a rare and benign tumor. Knowledge of this tumor is lacking among physicians and it is often mistaken for another lesion such as a gastrointestinal stromal tumor, leiomyoma or leiomyosarcoma and therefore surgically resected. Unless it is causing bleeding or obstruction, resection of this lesion is not necessary because of its benign nature. Currently, endoscopic examination is not sufficient to differentiate gastric adenomyoma from other mural lesions, and the mainstay of diagnosis remains histology and IHC evaluation [11]. Although gastric adenomyoma is a rare lesion, it must be considered when contemplating a diagnosis of a gastrointestinal stromal tumor or another mural gastric lesion. This report highlights the utility of using histology and IHC stains on a biopsy of a mural gastric lesion that microscopically consists of spindle cells and epithelium in order to avoid an unnecessary surgical resection.
This study is supported by the review of the modern literature which demonstrates that diagnostic uncertainty or misdiagnosis was the reason behind the decision for the resection of these lesions (Table 1). It appears in most cases that resection was driven by clinical presentation, mural nodule and the assumption that these lesions were a GIST. On resection, interestingly, most current case reports used histological features to suggest a diagnosis of gastric adenomyoma and only 3 reports used IHC of CK7 (+) as the collaborative evidence for this rare diagnosis.   Figure 4: Gastric adenomyoma diagnostic algorithm. FNA of a mural gastric lesion that reveals both spindle cells and epithelium should be evaluated for leiomyoma, GIST, and adenomyoma using desmin, CKIT, DOG1, and PDGF staining. A sample that stains negative for these can be diagnosed as a gastric adenomyoma.
Avoiding surgery for an asymptomatic mural-based lesion that is benign should be the goal of all who manage gastric pathology: surgeon, gastroenterologist and pathologist alike. We would disagree with the literature that suggests resection is the only method to accurately diagnose this disease. In fact, if one looks at the histologic components and adds in the IHC evaluation, there is a compelling argument that this diagnosis can be made on a EUS directed FNA. Here we present for the first time a simple algorithm to make the diagnosis of a gastric adenomyoma preoperatively (Figure 4). In this approach, the endoscopist must first decide if the lesion is a luminal one or muralbased. If a luminal lesion is considered, then other diagnoses should be entertained, such as gastric cancer. Subsequently, if the lesion is considered mural, multiple FNAs should be obtained and histologically evaluated for the presence of epithelial cells. It is important to note that tracking of gastric epithelium can occur in this setting and confound the histology. However, if epithelial elements are seen, then a combination of IHC staining should be ordered focusing on desmin (+) and CK7 (+) to support a gastric adenomyoma and CD117, DOG1 and PDGF all negative to exclude a GIST tumor.
Gastric adenomyomas is a benign tumor that is mural based in the antrum of the stomach. Unfortunately, the rarity of the diagnosis allows it to be easily confused and overlooked for the more common GIST tumors of the stomach. Although surgery has become a safer and better-tolerated management of gastric lesions (laparoscopic or robotic resections), it still has inherent risks and the morbidity, mortality and costs are not insignificant. We presented our case of a gastric adenomyoma and its mistaken preoperative diagnosis as a point of reference and review of the modern literature to demonstrate that a simple and concise algorithm can obviate most of these mistaken identities.