gms | German Medical Science

Objective: Magnetic resonance imaging (MRI) has greatly improved pre-surgical imaging in vestibular schwannomas (VS). Still to date two questions are difficult to answer: 1. the exact intrameatal tumour extension, and 2. the tumour relation to nerves in the cerebellopontine angle. By enhanced CISS (constructive interference in steady state) technique, this situation might be improved.

Methods: In 2010 and 2011, routine pre-operative MRI was supplemented by enhanced CISS MRI without any additional contrast application in 30 patients (9 female, 21 male, mean age 52 years). Enhanced CISS and enhanced T1 sequences were compared for tumour extension along the nerve axis in the transversal plane and perpendicular to this in the sagittal plane. Intrameatal tumour extension was classified by 5 grades (grade °1 25% involvement, °2 50%, °3 75%, °4 100% up to the fundus, °5 cochlea infiltration). Ipsi- and contra-lateral visibility of VII^th and VIII^th cranial nerves was compared. Data were correlated with pre-operative auditory function and intra-operative findings.

Results: Transverse tumour diameter in standard enhanced T1 measured 19 mm compared to 23.4 mm in enhanced CISS sequence, while sagittal tumour extension measured 15.6 mm compared to 16.7 mm in enhanced CISS sequence. Grade 4 intrameatal tumour extension up to the fundus was correctly predicted by enhanced CISS sequence in 28 cases, while T1 failed to identify this in 3 cases. Position of the facial nerve could be identified on 16 enhanced CISS images and of the cochlear nerve on 9 CISS sequences, while this was never possible on conventional enhanced T1 images.

Conclusions: Enhanced T1 sequences underestimate the tumour borders and thereby the tumour extension in transverse and sagittal planes compared to enhanced CISS sequence. The correct judgement of tumour extension in the CP angle and in the meatus by enhanced CISS technique could be proven at surgery of the VS. Moreover, the identification of nerves versus vessels in the CPA is more easily achieved by enhanced CISS sequence compared to non-enhanced CISS and was positively verified at surgical exploration. The correct pre-operative evaluation of the likely tumour extension is important also for patient counselling. In view of these advantages enhanced CISS sequence is suggested as a new standard imaging method for pre-surgical planning in VS.