The Clinical and Pathological Features of Depressed Type Colorectal Neoplasms and the Significance of Pit Pattern Diagnosis

Abstract

Introduction: At one time, most colorectal carcinomas were thought to develop from protruded polyps. Recent advances in endoscopic diagnosis and colonoscope technology have revealed the existence of many flat and depressed types of neoplasms. GIE, published in Oct. 2008, widely introduced those lesions as nonpolypoid mucosal colorectal neoplasms (NMCN). We have detected more than 600 depressed type neoplasms at Akita Red Cross Hospital and our Unit during 1985-2008. Depressed type neoplasms are assumed to emerge directly from normal epithelium without going through a stage of adenoma, which is mentioned as the “de novo” carcinogenesis. “De novo” sequence possibly may be main route of development of colorectal cancer. Aim: To evaluate the clinical and pathological natures and validity of pit pattern diagnosis (Kudo's classification) on depressed type colorectal neoplasms. Methods: From Apr. 2001 to Jun. 2008, we retrospectively evaluated 10,212 colorectal neoplasms, excluding advanced cancers, which removed endoscopically or surgically at our Unit. We evaluated a correlation between submucosal invasive rates and size, morphological features and pit patterns. Result: The submucosal invasive rate of depressed type neoplasms reached 64.1% (98/153). Meanwhile, the overall invasive rates of flat and protruded type neoplasms were 2.6% (98/3772) and 3.2% (204/6288), respectively. The submucosal invasive rates were 6.5% in lesions not exceeding 5 mm, 60.8% in those from 6-10 mm, and 89.2% in those from 11-15 mm in diameter. In contrast, the invasive rates in flat type and protruded type neoplasms were 0% and 0.04% for those less than 5mm in diameter. Most (90.9% and 91.7%) of the protruded and flat type neoplasms showed type IIIL or IV pit patterns, whereas 94.3% of the depressed type neoplasms were characterized by type IIIS, VI, or VN pit patterns. Only 0.63% of the lesions with type IIIL, and IV pit patterns were invasive cancers. On the other hand, 2.4% of the lesions with type IIIS pit pattern, 34.5% of those of type VI and 91.1% of those of type VN were invasive carcinomas regardless of its gross appearance. Type VI reflected histological structural atypism outgrowth of cancerous glands, and type VN, which lacks of superficial microstructure, reflected exposing desmoplastic reaction of deeply invasive submucosal components to the surface. Conclusion: We have revealed that depressed type neoplasms grow rapidly and invade the submucosa even at an early stage. With magnifying colonoscopies, the pit pattern diagnosis, which correlated well with the histological diagnosis, is available for assessing the depth of the lesions and selecting appropriate therapies.