A Rare Case of Heavily Calcified Gastrointestinal Stromal Tumor Diagnosed by Endoscopic Ultrasound-Guided Core Biopsy

Introduction: Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor within the GI tract, about 2% of primary GI tumors. Up to 50% of GISTs follow a malignant clinical course highlighting the importance of accurate diagnosis and management. Focal calcifications are not uncommon but heavy calcifications in GISTs are rare and scarcely reported in literature. Heavily calcified subepithelial lesions can be a diagnostic challenge as they are often asymptomatic, incidentally found, poorly visualized on EUS, and yield low on biopsy. This can result in diagnostic delay and management. Case Description/Methods: A 67-years-old female with chronic back pain underwent X-ray of the spine that showed an oval calcific area in the LUQ. she denied abdominal pain, nausea, vomiting, or weight loss. A CT was performed to characterize the lesion which showed an oval-shaped, mixed density, calcified lesion arising from the proximal body of the stomach, measuring 3.1 by 3.5. She was referred for EUS sampling. EUS showed a subepithelial calcified lesion in the gastric body arising from the muscularis propria. Depth of invasion could not be assessed secondary to severe posterior acoustic shadowing. Two passes were made using a 22-gauge biopsy needle (Acquire; BSCI). Microscopic pathology examination showed spindle cell neoplasm with immunohistochemical stains positive for CD117 and CD34 consistent with GIST (figure 4-5-6). She underwent robotic wedge resection of the GIST. Discussion: Heavily calcified mass is an uncommon presentation of GIST that has been reported in few cases. It is important to differentiate heavily calcified GISTs from other benign calcified lesions such as calcifying fibrous tumor, pancreatic cyst, schwannoma, leiomyoma and leiomyosarcoma, as management may differ. EUS guided sampling is the preferred way of diagnosing subepithelial lesions, but, heavy calcification limits EUS visualization of the tumor secondary to acoustic shadowing and/or results in inadequate tissue sampling. Consequently, many calcified gastric tumors undergo surgery without definitive pre-operative diagnosis. Here we present the first case of heavily calcified GIST diagnosed via EUS guided core needle biopsy. Imaging is limited due to posterior acoustic shadowing but needle biopsy can still be safely performed by adjusting the depth of needle puncture to the size of the lesion based on C-S imaging. We recommend FNB over FNA to maximize specimen yield and overcome the low cellularity of calcified subepithelial lesions.Figure 1.: Fig. 1: X-ray showing an oval calcified mass in left upper abdomen. Fig. 2: CT abdomen showing exophytic gastric mass containing dense areas of calcification. Fig. 3: EUS showing a calcified lesion with posterior acoustic shadowing arising from the muscularis propria. Fig. 4-6: Microscopic pathology examination showed spindle cell neoplasm with calcifications.Figure 2Figure 3Figure 4Figure 5Figure 6