Measurement of aspiration pressure in cannula brain tumour biopsy and its correlation with ultrasonographic elastography.

Background: Stereotactic brain biopsy is to perform the manual aspiration tissue biopsy using a cannula on a syringe under stereotactic guidance to provide histological confirmation. Excessive vacuum aspiration increases the risk of haemorrhage. Manual aspiration relies on the surgeon's experience while the minimum vacuum pressure is unknown.

Objectives: 1. To assess the aspiration vacuum pressure range in cannula brain tumour biopsy; 2. To understand the correlation of ultrasound elastography data with the aspiration pressure.

Methods: This prospective study has recruited 10 patients for stereotactic brain tumour biopsy. With the use of ultrasound elastography, strain ratio of the lesion was assessed in real time before biopsy. Vacuum aspiration pressures were recorded using a T-connector pressure sensor during the stereotactic biopsy.

Results: A total of 11 biopsies were taken from 10 patients, including a bilateral biopsy for a patient with bifrontal lesions. The diagnostic yield was 100% in all the 10 patients with no symptomatic haemorrhage (but 2 subclinical haemorrhages in CT scan) nor infection. The vacuum pressures ranged from 40.34 to 65.61 kPa and the strain-ratio ranged from 0.405 to 2.74. Strain ratio of the lesion at the lower range required a lower range of aspiration pressure, whereas lesions of Strain ratio over 0.45 required a higher range of aspiration pressure.

Conclusion: A vacuum pressure of 40 to 66 kPas is safe and adequate for biopsy of various types of tumours with heterogenous elastographic characters. Ultrasonographic elastography may be a real-time guide for the minimum vacuum pressure required for biopsy.