Does the incidence of unexpected malignancy in 'benign' rectal neoplasms undergoing trans-anal endoscopic...

Mucosectomy by trans-anal endoscopic microsurgery (TEMS) allows safe and effective excision of benign rectal lesions. Preoperative endoscopic, clinical and ultrasonographic assessment aims to select benign lesions whilst avoiding inappropriate mucosectomy in lesions with malignancy. This study examines the relationship between lesion morphology and accurate benign preoperative classification of rectal lesions undergoing TEMS.

Primary lesions preoperatively assessed as benign were identified from a prospective TEMS database. Operative specimen morphology was independently classified by two blinded investigators, using photographs, into flat-sessile, exophytic or mixed morphology. The accuracy of the preoperative assessment by rectal ultrasonography was compared with the results of histological examination of the excised specimen (χ(2) and Fisher's exact tests).

Of 167 lesions with adequate data, the morphological classification showed 60 flat-sessile, 56 mixed morphology and 51 exophytic tumours, of which 5, 7 and 9, respectively, contained unexpected malignancy (P=0.48). Accurate preoperative assessment of a lesion as benign occurred in 89% of flat-sessile and mixed morphology (n=55 and 49, respectively) and in 70% of exophytic lesions (n=36) (P=0.01). Only the exophytic group contained patients in whom preoperative endoscopic and ultrasonographic staging could not be confidently made (uTx). Histology demonstrated six of the seven uTx cases to be benign.

In this study exophytic polyps were less likely to be accurately classified as benign using preoperative ultrasonography/endoscopy when compared with flat-sessile or mixed morphology polyps.