Intraoperative cytology (squash smear) in neurosurgical practice – pitfalls in diagnosis experience based on 3057 samples from a single institution

TLDR

The smear technique is challenging for neuropathologists, and this study reports the largest Indian series of intraoperative cytology, noting tuberculosis as the most common infection. The study retrospectively evaluated 3,057 CNS lesions from 1988‑2005 to assess the usefulness, accuracy, and diagnostic pitfalls of squash smear cytology in neurosurgical practice. Squash smears were stained with 1 % alcoholic toluidine blue and compared to histological diagnoses to determine diagnostic accuracy. Diagnostic accuracy of squash smears ranged from 83 % to 86 % (mean 85 %), with the highest correlation for schwannoma (96.6 %) and pituitary adenoma (92.2 %); infections accounted for 380 cases, and the technique proved reliable and rapid, especially when combined with clinical and neuroimaging information.

Abstract

The smear technique is challenging for a neuropathologist where rapid and accurate diagnosis is to be given on small biopsies. The present study, a large retrospective analysis of squash smears in neurosurgical practice, was conducted to assess the usefulness, accuracy and the diagnostic pitfalls of smear diagnosis.The authors analysed 3057 central nervous system (CNS) lesions sent for intraoperative cytology (IC) during the years 1988-2005. The stain used was 1% alcoholic toluidine blue. The smear diagnosis was compared with the histological diagnosis to evaluate the diagnostic accuracy.Diagnostic accuracy irrespective of lesion and site ranged from 83.0% to 86.0% per year (mean=85%). The highest rate of correlation among common brain tumours was noted in schwannoma (96.6%) and pituitary adenoma (92.2%), followed by meningiomas (88.9%), astrocytomas (88.4%), chordomas (86.4%) and neurocytomas (86.9%). Infections as a whole contributed 380 cases. The most common infection was tuberculosis.This is the largest series reported from India to the best of our knowledge. Squash smear technique is a very reliable and rapid method of intraoperative diagnosis. Knowledge of clinical and neuroimaging details helps the experienced neuropathologist to improve the diagnostic accuracy.