Observer variation in the assessment of the histopathologic diagnosis of acute appendicitis

The objectives of this study were to determine observer variation in the assessment of the histopathologic diagnosis of acute appendicitis.

Two consultant pathologists independently evaluated 415 appendectomy specimens (set I). After a consensus conference at which the observers unified the criteria of the diagnosis of acute appendicitis, another 396 appendectomy specimens (set II) were evaluated. To calculate the intra-observer variation, one observer evaluated set II once more. Finally, using the consensus diagnosis as the final diagnosis, the diagnostic accuracy of the surgeon, the primary pathology report, and the two observer evaluations was calculated.

In set I no difference was found in the level of agreement on the diagnosis of acute appendicitis versus other diagnoses, and a kappa value of 0.85 was obtained. In set II a kappa value of 0.88 was obtained, which was not significantly different from the kappa value in set I. However, the consensus conference did increase the level of agreement on the diagnosis of acute appendicitis. The intra-observer variation was calculated, and a kappa value of 0.88 was obtained. The cases in which the observers disagreed on a positive diagnosis were cases of mild appendicitis. The question remains how many specimens would have shown these changes if all tissue had been developed for microscopy. The observers' diagnoses were the most reliable, and there was a significant decrease in the diagnostic accuracy compared with both the primary pathology report and the surgeon's opinion, the last one being the least accurate.

These observations stress how important it is for the pathologist to discuss the diagnostic criteria of the diagnosis of acute appendicitis and for the surgeon to go back to the patient's record and look up the histopathologic diagnosis.