Objective: To measure the intra- and interobserver error in size estimation of acoustic schwannomas
from magnetic resonance imaging (MRI) scans by experienced radiologists to determine
whether small amounts of tumor growth that may affect management (2 mm) could be reliably
measured in clinical practice.
Design: Duplicated, blinded size estimation of acoustic neuromas (according to American Academy
of Otolaryngology-Head and Neck Surgery guidelines, 1995) from MRI scans of patients
with acoustic neuromas.
Setting: Tertiary referral teaching hospital and DGH.
Participants: Four radiologists (including 2 dedicated neuroradiologists) measuring positive MRI
scans of 26 patients with an acoustic neuroma.
Main Outcome Measure: Intraradiologist and inter-radiologist repeatability coefficients in millimeters
for the maximal tumor diameter in the anteroposterior (AP) axis, medial-longitudinal
(ML) axis, and the square-root of the product of these two measurements. Repeatability
coefficients give the 95% range within which the differences in repeated measurements
lie.
Results: The intraradiologist repeatability for AP and ML measurements ranged from 1.51 to
6.03 mm and 2.01 to 3.83 mm, respectively. The repeatability of the square-root of
the product ranged from 1.43 to 4.94 mm. The interradiologist repeatability was 6.48
mm and 7.46 mm for the AP and ML measurements, respectively, giving a repeatability
of 3.65 mm for the square-root of the product.
Conclusion: The study indicates that, in routine clinical practice, differences in tumor size
of the order of 2 mm cannot be reliably measured, even by the same radiologist. Thus,
reported growth of acoustic tumors should be interpreted with caution, especially
if this is the criterion for recommending treatment.
