OBJECTIVETo investigate clinicopathological characteristics of colorectal sessile serrated adenoma/polyp (SSA/P) and its differential diagnosis from other serrated lesions.

METHODSClinicopathological features of all cases of colorectal serrated lesions from 5 209 colorectal biopsy samples at Shanghai Tongji Hospital from 2008 to 2013 were reviewed. Three hundred and fifty-three cases of serrated lesions were erolled in the study. Morphological features of SSA/P were investigated with an emphasis on histologic criteria for diagnosis and a literature review was performed.

RESULTSThree hundred and fifty-three cases of serrated lesions were identified, including 25 SSA/P (7.1%), 278 hyperplastic polyp (HP, 78.8%), and 44 traditional serrated adenoma (TSA, 12.5%). Twenty-five patients with SSA/P consisted of 16 males and 9 females with a mean age of 62.2 years (aged 34-84 years) and the lesions involved sigmoid colon (14 cases), ascending colon (9 cases), rectum (1 case) and transverse colon (1 case). Grossly, the majority of SSA/P was sessile with an averaged size of 0.73 cm. Histologically, typical SSA/P had elongated crypts with prominent serration and distorted crypts architecture. The detection rates of crypts dilatation and branching in SSA/P and HP were 100% (25/25) and 24% (12/50, P < 0.01), 72% (18/25) and 4% (2/50, P < 0.01), respectively. Morphological features observed only in SSA/P included L-shaped crypts (48%, 12/25), pseudo infiltration of mucosa muscle (16%, 4/25), atypical nuclei (32%, 8/25), and increased mucus secretion (24%, 6/25).

CONCLUSIONSSSA/P microscopically shows prominent serration and abnormal architectures of crypts. Complete tissue sectioning and correct embedding are helpful for the diagnosis. SSA/P without cytological dysplasia should be distinguished from HP, especially those with only a few distorted crypts.