Case Report Sporadic segmental Interstitial cell of cajal hyperplasia (microscopic GIST) with unusual diffuse longitudinal growth replacing the muscularis propria: differential diagnosis to hereditary GIST syndromes

Gastrointestinal stromal tumors (GIST) are the most common primary mesenchymal neoplasms of the GI tract [1]. GISTs are KIT-positive and KIT-signalling driven neoplasms that most commonly originate in the stomach and small bowel but may occur at any site along the GI tract [2]. GISTs are uncommon in the colon and rectum (5-10%) [2]. Somatic mutation in the cKIT (~80%) [3,4] and PDGFRA (~10%) [5,6] are considered initiating early molecular events in a majority of cases. GISTs usually present as a discrete well-circumscribed but nonencapsulated tumor mass with strikingly varied gross appearances including luminal-polypoid, intramural, extramural, pedunculated forms or a variable combination thereof [2,7]. A few GISTs were reported to arise within a “Meckel diverticulum” [7,8], but the diverticular aspect in most of them is obviously the consequence of deep cavitating tumor ulceration with central necrosis and occasional cyst formation [7,9].