Both vertical and transverse sections are used in the histologic interpretation of alopecia biopsy specimens. Although a combination of the two may be optimal, the pathologist is frequently only provided with a single specimen. Even though the trend in recent years has been toward transverse sections in this setting, we are not aware of any published data directly comparing the two methods.

One hundred two consecutive archived hair biopsy accessions that demonstrated comparable vertical and transverse sections were examined twice, each time in a random order. The pathologist's interpretation based only on the vertical sections and an interpretation based only on the transverse sections were compared with the original biopsy report, which had been based on the combination of vertical and transverse sections.

In 76 cases, all 3 diagnoses were concordant (ie, the diagnosis made with vertical sections alone, the diagnosis made with transverse sections alone, and the original diagnosis were all in agreement). In 2 cases, neither the diagnosis made with vertical sections alone nor the diagnosis made with transverse sections alone were in full agreement with the original diagnosis. In 20 cases, only the diagnosis made with vertical sections was concordant with the original diagnosis. In 4 cases, only the diagnosis made with transverse sections alone was concordant with the original diagnosis.

Our practice is heavily weighted toward scarring alopecia, and the results of our study may not be applicable to practices weighted toward other forms of alopecia. Because the cases had been signed out over a period of several years, the nomenclature for some entities changed. For the purposes of our study, we counted the diagnoses of follicular degeneration syndrome and idiopathic pseudopelade to be subtypes of (and concordant with) a diagnosis of central centrifugal cicatricial alopecia. In some cases, a definitive diagnosis was not possible at the time of the original diagnosis, but rather the pathologist had provided a histologic description and a differential diagnosis. For purposes of this study, an interpretation was considered to be concordant with the original descriptive diagnosis if all of the important histologic features were identified that had been described in the original report. Sampling error could have contributed to discordant diagnoses, but would be expected to affect both vertical and transverse samples in a random manner.

The combination of vertical and transverse sections is superior to either alone. Although transverse sections have revolutionized the evaluation of alopecia, in this study, the diagnosis made with vertical sections alone had a higher concordance rate with the combination than did transverse sections alone. As there are advantages and disadvantages inherent in either method, when only a single biopsy specimen is submitted, it may be sectioned either vertically or transversely, at the discretion of the pathologist. With either method, serial step sections should be obtained to reduce the risk of missing important histologic findings.