CAN HISTOPATHOLOGISTS RELIABLY DIAGNOSE MOLAR PREGNANCY

Aims-To assess the degree of difficulty in diagnosing partial mole by analysing intraobserver and interobserver agreement among a group of p athologists for these diagnoses. Methods-Fifty mixed cases of partial mole, complete mole, and non-molar pregnancy were submitted to seven h istopathologists, two of whom are expert gynaecological pathologists; the other five were district general hospital consultants, one of whom works in Australia. These participants gave each slide a firm diagnos is of either partial mole, complete mole, or non-molar pregnancy. Some 12 months later, the slides were recoded and again submitted for a se cond diagnostic round to assess intraobserver as well as interobserver agreement. Standard histological criteria for each diagnostic categor y were circulated with the slides. Results-Kappa statistics showed tha t complete mole could be reliably distinguished from non-molar pregnan cy, but neither non-molar pregnancy nor complete mole could be easily differentiated from partial mole. In only 35 out of 50 cases was there agreement between five or more of the seven participants. Agreement b etween the expert gynaecological pathologists was no better than for o thers in the group. Interestingly, the intraobserver agreement for eac h pathologist was good to excellent. Conclusions-These results imply t hat the reported histological criteria are either not being applied co nsistently or that they are lacking in practical use. An atypical grow th pattern of trophoblast, rather than the polar accentuation seen in normal first trimester pregnancies, seems to be the important diagnost ic histological feature for partial mole. Ploidy studies might also he lp with problem cases.