Recognition of parametrial invasion, an important landmark when treating cervical cancer

Purpose: Histological assessment of parametrial invasion in uterine cervical cancer is often subjective due to the parametrium being a loosely defined structure without apparent definitive landmarks. This study defines a precise and consistent histological landmark for the parametrium. Methods: Based on study of cervico-parametrial junctions in 22 type III radical hysterectomy specimens from FIGO stage IB/IIA patients, three candidate histological landmarks were tested for ease in determination and reliability in 66 hysterectomy specimens with FIGO stage IIB tumors. The candidate landmarks were abrupt narrowing point of vascular branches, adipose/loose connective tissue of parametrium, and presence of a distinct smooth muscle layer in the outermost cervical wall. Results: All uteri had a distinct smooth muscle layer in outermost cervical wall. The layer was compact, circumferential, and continuous with the corpus above and vagina below. It clearly distinguished parametrium from cervical wall, especially when the Masson trichrome stain was used which differentiated fibrous tissue from smooth muscle. Smooth muscle bundles are also present in the parametrium, but course perpendicularly or diagonally to the cervical wall, clearly distinguishable from the circular smooth muscle in the outer wall. With clear histological criteria, concordance rates among three pathologists rose from 55% to 98%. Conclusion: Clear histological criteria together with the use of Masson trichrome stains to distinguish smooth muscle from fibrous tissue improved concordance rates in identifying parametrial invasion by tumor to near 100%.