The ratio of facial nerve to facial canal as an indicator of entrapment in Bell's palsy: A study by CT and MRI.

OBJECTIVES: To find out if the ratio of facial nerve to facial canal diameter plays any role in the etiopathogenesis and grade of Bell's palsy. PATIENTS AND METHODS: Twenty-nine consecutive patients (16 females, 13 males) diagnosed with unilateral Bell's palsy were enrolled into the study. At admission, 5 patients were grade V, 11 were grade IV, 11 were grade III and 2 were grade II. The grade of Bell's palsy was documented by House-Brackmann facial nerve grading system at admission, 15th day, 1st month and 3th month. Temporal MRI and CT scans were obtained at the time of diagnosis. Diameter of facial nerve and facial canal at the middle of five different segments were measured equidistantly at the same workstation. Both sides of every patient (affected and unaffected) were measured by one radiologist who was not informed about the side of the paralysis. MRI and CT values of each segment were compared between affected and unaffected sides. In addition, FN/FC ratio of affected and non-affected sides was calculated and compared for each segment. We also analyzed if a relationship exists between above-mentioned measurements and the House-Brackmann grade. RESULTS: Considering MRI values; statistically significant thickening of facial nerve between affected and unaffected sides was found at labyrinthine (p = 0.012), tympanic (p = 0.023) and geniculate parts (p = 0.04). Considering CT values; statistically significant difference between affected and unaffected sides was not found at any segment. Comparison of FN/FC ratio of both sides revealed statistically significant increment of the affected side at labyrinthine segment (p = 0.015) and geniculate ganglion (p = 0.032). We determined positive correlation between diameter of FN and HB grade at labyrinthine segment (p = 0.03, R = 0.531). On the other hand, we determined negative correlation between diameter of FC and HB grade at labyrinthine segment (p < 0.001, R = -318). A positive correlation between HB grade and FN/FC ratio was found only at the labyrinthine segment (p = 0.003, R = 0.673). CONCLUSION: FN/FC ratio of labyrinthine segment and geniculate ganglion was found to be increased in patients with Bell's palsy. In addition, a positive correlation was determined between this ratio and grade of Bell's palsy particularly at labyrinthine segment. Basing the current study, if FN decompression is recommended in Bell's palsy patients with objective findings of bad prognosis, conservative surgery targeting the labyrinthine segment and geniculate ganglion alone might be safer.

The role of facial canal diameter in the pathogenesis and grade of Bell's palsy: a study by high resolution computed tomography / O papel do diâmetro do canal facial na patogenia e grau de paralisia de Bell: estudopor tomografia computadorizada de alta resolução

Abstract Introduction: The exact etiology of Bell's palsy still remains obscure. The only authenticated finding is inflammation and edema of the facial nerve leading to entrapment inside the facial canal. Objective: To identify if there is any relationship between the grade of Bell's palsy and diameter of the facial canal, and also to study any possible anatomic predisposition of facial canal for Bell's palsy including parts which have not been studied before. Methods: Medical records and temporal computed tomography scans of 34 patients with Bell's palsy were utilized in this retrospective clinical study. Diameters of both facial canals (affected and unaffected) of each patient were measured at labyrinthine segment, geniculate ganglion, tympanic segment, second genu, mastoid segment and stylomastoid foramen. The House-Brackmann (HB) scale of each patient at presentation and 3 months after the treatment was evaluated from their medical records. The paired samples t-test and Wilcoxon signed-rank test were used for comparison of width between the affected side and unaffected side. The Wilcoxon signed-rank test was also used for evaluation of relationship between the diameter of facial canal and the grade of the Bell's palsy. Significant differences were established at a level of p = 0.05 (IBM SPSS Statistics for Windows, Version 21.0.; Armonk, NY, IBM Corp). Results: Thirty-four patients - 16 females, 18 males; mean age ± Standard Deviation, 40.3 ± 21.3 - with Bell's palsy were included in the study. According to the HB facial nerve grading system; 8 patients were grade V, 6 were grade IV, 11 were grade III, 8 were grade II and 1 patient was grade I. The mean width at the labyrinthine segment of the facial canal in the affected temporal bone was significantly smaller than the equivalent in the unaffected temporal bone (p = 0.00). There was no significant difference between the affected and unaffected temporal bones at the geniculate ganglion (p = 0.87), tympanic segment (p = 0.66), second genu (p = 0.62), mastoid segment (p = 0.67) and stylomastoid foramen (p = 0.16). We did not find any relationship between the HB grade and the facial canal diameter at the level of labyrinthine segment (p = 0.41), tympanic segment (p = 0.12), mastoid segment (p = 0.14), geniculate ganglion (p = 0.13) and stylomastoid foramen (p = 0.44), while we found significant relationship at the level of second genu (p = 0.02). Conclusion: We found the diameter of labyrinthine segment of facial canal as an anatomic risk factor for Bell's palsy. We also found significant relationship between the HB grade and FC diameter at the level of second genu. Future studies (MRI-CT combined or 3D modeling) are needed to promote this possible relevance especially at second genu. Thus, in the future it may be possible to selectively decompress particular segments in high grade BP patients.

Resumo Introdução: A etiologia exata da paralisia de Bell ainda permanece obscura. Os únicos achados confirmados são a inflamação e o edema do nervo facial (NF) que levam ao aprisionamento no canal facial. Objetivo: Identificar se há alguma relação entre o grau de paralisia de Bell e o diâmetro do canal facial e também estudar qualquer possível predisposição anatômica do canal facial para a paralisia de Bell incluindo as partes que ainda não foram estudadas. Método: Os prontuários médicos e exames de tomografia computadorizada de 34 pacientes com paralisia de Bell foram avaliados neste estudo clínico retrospectivo. Os diâmetros de ambos os canais faciais (acometidos e não acometidos) de cada paciente foram medidos no segmento labiríntico, gânglio geniculado, segmento timpânico, segundo joelho, segmento mastoideo e forame estilomastoideo. As escalas de House-Brackmann (HB) de cada paciente na apresentação inicial e três meses após o tratamento foram avaliadas a partir de seus prontuários. O teste t de amostras pareadas e o teste dos postos sinalizados de Wilcoxon foram usados para comparação de largura entre o lado acometido e o lado não acometido. O teste de postos sinalizados de Wilcoxon também foi usado para avaliação da relação entre o diâmetro do canal facial e o grau de paralisia de Bell. Diferenças significativas foram estabelecidas em um nível de p = 0,05 (IBM SPSS Statistics for Windows, versão 21.0; Armonk, NY, IBM Corp). Resultados: Foram incluídos 34 pacientes - 16 mulheres, 18 homens; idade média ± desvio padrão (DP), 40,3 ± 21,3 com paralisia de Bell. De acordo com o sistema de classificação do nervo facial de HB, oito pacientes eram de grau V, seis de grau IV, 11 de grau III, oito de grau II e um de grau I. A largura média no segmento labiríntico do canal facial no osso temporal acometido foi significativamente menor do que o equivalente no osso temporal não acometido (p = 0,00). Não houve diferença significativa entre os ossos temporais acometidos e não acometidos no gânglio geniculado (p = 0,87), segmento timpânico (p = 0,66), segundo joelho (p = 0,62), segmento mastoide (p = 0,67) e forame estilomastoideo (p = 0,16). Não houve relação entre o grau de HB e o diâmetro do canal facial no nível do segmento labiríntico (p = 0,41), segmento timpânico (p = 0,12), segmento mastoideo (p = 0,14), gânglio geniculado (p = 0,13) e forame estilomastoideo (p = 0,44), mas houve uma relação significativa no nível do segundo joelho (p = 0,02). Conclusão: O diâmetro do segmento labiríntico do canal facial foi um fator de risco anatômico para a paralisia de Bell. Também houve relação significativa entre o grau de HB e o diâmetro do CF no nível do segundo joelho. Estudos futuros (RM-TC combinadas ou modelagem 3D) são necessários para promover essa possível relevância especialmente no segundo joelho. Assim, no futuro, pode ser possível descomprimir segmentos específicos em pacientes com alto grau de PB.

The role of facial canal diameter in the pathogenesis and grade of Bell's palsy: a study by high resolution computed tomography.

INTRODUCTION: The exact etiology of Bell's palsy still remains obscure. The only authenticated finding is inflammation and edema of the facial nerve leading to entrapment inside the facial canal. OBJECTIVE: To identify if there is any relationship between the grade of Bell's palsy and diameter of the facial canal, and also to study any possible anatomic predisposition of facial canal for Bell's palsy including parts which have not been studied before. METHODS: Medical records and temporal computed tomography scans of 34 patients with Bell's palsy were utilized in this retrospective clinical study. Diameters of both facial canals (affected and unaffected) of each patient were measured at labyrinthine segment, geniculate ganglion, tympanic segment, second genu, mastoid segment and stylomastoid foramen. The House-Brackmann (HB) scale of each patient at presentation and 3 months after the treatment was evaluated from their medical records. The paired samples t-test and Wilcoxon signed-rank test were used for comparison of width between the affected side and unaffected side. The Wilcoxon signed-rank test was also used for evaluation of relationship between the diameter of facial canal and the grade of the Bell's palsy. Significant differences were established at a level of p=0.05 (IBM SPSS Statistics for Windows, Version 21.0.; Armonk, NY, IBM Corp). RESULTS: Thirty-four patients - 16 females, 18 males; mean age±Standard Deviation, 40.3±21.3 - with Bell's palsy were included in the study. According to the HB facial nerve grading system; 8 patients were grade V, 6 were grade IV, 11 were grade III, 8 were grade II and 1 patient was grade I. The mean width at the labyrinthine segment of the facial canal in the affected temporal bone was significantly smaller than the equivalent in the unaffected temporal bone (p=0.00). There was no significant difference between the affected and unaffected temporal bones at the geniculate ganglion (p=0.87), tympanic segment (p=0.66), second genu (p=0.62), mastoid segment (p=0.67) and stylomastoid foramen (p=0.16). We did not find any relationship between the HB grade and the facial canal diameter at the level of labyrinthine segment (p=0.41), tympanic segment (p=0.12), mastoid segment (p=0.14), geniculate ganglion (p=0.13) and stylomastoid foramen (p=0.44), while we found significant relationship at the level of second genu (p=0.02). CONCLUSION: We found the diameter of labyrinthine segment of facial canal as an anatomic risk factor for Bell's palsy. We also found significant relationship between the HB grade and FC diameter at the level of second genu. Future studies (MRI-CT combined or 3D modeling) are needed to promote this possible relevance especially at second genu. Thus, in the future it may be possible to selectively decompress particular segments in high grade BP patients.