Acoustic schwannomas: awareness of radiologic error will reduce unnecessary treatment.
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.


METHODS
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.


METHODS
Tertiary referral teaching hospital and DGH.


METHODS
Four radiologists (including 2 dedicated neuroradiologists) measuring positive MRI scans of 26 patients with an acoustic neuroma.


METHODS
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 inter-radiologist 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.


CONCLUSIONS
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.
Marshall
Andrew H
AH
Department of Otolaryngology, Queen's Medical Center NHS Trust, University Hospital, Nottingham, UK.
Owen
Victoria M F
VM
Nikolopoulos
Thomas P
TP
O'Donoghue
Gerard M
GM
D006801:Humans; D008279:Magnetic Resonance Imaging; D009464:Neuroma, Acoustic / Q000175:diagnosis*; D015588:Observer Variation; D015203:Reproducibility of Results; D016037:Single-Blind Method; D019564:Unnecessary Procedures