Intentional Insertion of Air to Predict the Diagnostic Accuracy of Stereotactic Biopsy and a Uniform Grading System for Reporting

Background and Objectives: Stereotactic biopsies are a relatively safe and reliable way of tissue diagnosis and characterization of eloquent area lesions/neoplasm. However, predicting the accuracy of the site of biopsy with the desired/planned site is not always possible. We describe a technique to identify the precise location of the biopsy site in the post-operative computed tomography (CT) scan using the injection of a low volume of air into the biopsy cannula. Methods: Hundred consecutive biopsies were performed in 80 adults/20 children (59 males/41 females, median age 51 years) over 3 years, consisting of 75 frameless and 25 frame-based stereotactic biopsies. After the biopsy specimens had been collected, a small volume of air (median 1 cc) was injected into the site. Post-operative CT was done within 4 hours of the biopsy to see the site of the air bubble, and the same was correlated with the histopathological accuracy. Results: Intra-cranial air in the selected target was present in 95 patients (Grade 1 and 2), while the air was seen in the track (Grade 3) in 3% and at an unrelated site (Grade 4) in 2% of cases. Both Grade 4 biopsies were negative on histopathology (diagnostic yield = 98%). Two negative biopsies were reported, which were both predicted with the Grade 4 biopsy. The grading allowed uniform reporting across series and eliminated the chance of upgrading/downgrading the report due to wrong site sampling within the lesion/neoplasm. Conclusion: The air-injection manoeuvre proposed for use in stereotactic biopsies of intra-cranial mass lesions is a safe and reliable technique that allows the exact biopsy site to be located without any related complications.