P1493 - Pancreatic Mesothelial Cyst Diagnosed via Endoscopic Ultrasound-Guided Fine Needle Aspiration and Through-The-Needle Biopsy

Ramon O. Minjares, MD¹, Shaadi Abughazaleh, MD², Patrick R. Reardon, MD², Michael Deavers, MD², Blythe Gorman, MD², Alberto O. Barroso, MD^3
1Underwood Center for Digestive Disorders, Houston Methodist Hospital, Houston, TX; ²Houston Methodist Hospital, Houston, TX; ³Houston Methodist Research Institute and Weill Cornell College of Medicine, Houston, TX

Introduction: Pancreatic cystic lesions are increasingly detected due to advanced radiographic modalities. Mesothelial cysts are rare benign cysts originating in the serous cavities or in organs closely associated with these mesothelial-lined cavities. Due to its rareness, pancreatic mesothelial cyst (PMC) is often mistaken for other diagnoses leading to surgical resection. This may represent the first case of a PMC diagnosed by endoscopic ultrasound (EUS)-guided fine needle aspiration (FNA) and through-the-needle biopsy (TTNB).

Case Description/Methods: A 71-year-old female with severe COPD and DM was found to have an incidental cyst in the pancreatic tail. The cyst was initially reported on a CT scan of the chest and measured 3.9 cm. The patient was completely asymptomatic. Initial EUS showed a multiseptated 4 cm cyst in the pancreatic tail with thin septations (no mural nodules or ductal communication). The cyst was not sampled during that examination and the patient was referred for surgery. The patient was presented in our multidisciplinary meeting and the decision was made to pursue EUS-guided FNA/TTNB given her significant comorbidities.




Repeat EUS showed an anechoic, multi-cystic, septated and distally enhancing lesion suggestive of a cyst in the pancreatic tail, not in obvious communication with the PD. The lesion measured 4 cm. Compartments were thinly septated. Diagnostic FNA was performed. Biopsies of the cyst were obtained using microforceps (Moray) through a 19-gauge needle.




Biopsies revealed a fibrous cyst wall lined by attenuated mesothelial cells. Cyst fluid analysis showed Amylase 5 U/L, CEA < 1.2 ng/mL, Glucose 103 mg/dL. Cytology was negative for malignancy. There were numerous large flat sheets of bland cells, morphologically compatible with mesothelial cells. No columnar epithelium, thick extracellular mucin, or significant cytologic atypia was seen. Staining for D2-40 and WT-1 (markers of mesothelial differentiation) were positive. Calretinin (mesothelial marker), chromogranin (neuroendocrine marker), and inhibin (serous cystadenoma marker) staining were negative on cell block sections. The overall findings were compatible with a mesothelial cyst.

Discussion: PMC can be diagnosed with EUS-guided FNA/TTNB which is technically feasible and effective. This highlights the important role of EUS-guided biopsy for the diagnosis of cystic lesions of the pancreas as some of these lesions can be left untreated without the need for surgical resection.



Disclosures:


Ramon O. Minjares, MD¹, Shaadi Abughazaleh, MD², Patrick R. Reardon, MD², Michael Deavers, MD², Blythe Gorman, MD², Alberto O. Barroso, MD³. P1493 - Pancreatic Mesothelial Cyst Diagnosed via Endoscopic Ultrasound-Guided Fine Needle Aspiration and Through-The-Needle Biopsy, ACG 2023 Annual Scientific Meeting Abstracts. Vancouver, BC, Canada: American College of Gastroenterology.