Morphological evaluation of the common crus of the semicircular canals of patients with BPPV

Paolo Gargiulo (1,2), Agnes Czenek (2), Hannes Petersen (3,4)

1) Heilbrigðis og upplýsingatæknideild, Landspítalinn 2) Heilbrigðisverkfræðisvið, tækni og verkfræðideild, Háskólinn í Reykjavík3) Háls-, nef- og eyrnadeild Landspitalans, Skurðsvið. 4) Líffærafræði, Læknadeild Háskóla islands.

Introduction BPPV is the most common cause of vertigo. Although there are system causes the presentation is unilateral. Therefore it is interesting to investigate if there are morphological changes causing this lateralization. For the calcium crystals of the utriculus to enter the posterior semicircular canal, they have to traverse the common crus. Differences between right and left might explain the unilaterally of the disease.The study aim is to search morphological differences between healthy and diseased inner ears developing measurements tools which allow to calculate the total length and the diameter of the common crus as well as it’s angulation using CT imaging and image processing techniques.

Methods4 voluntary patients suffering from BPPV are enrolled into the study. Special CT scanning protocol is employed to scan the region of interest between temporal and zygomatic bone with image matrix of 768 × 768 pixels, slice thickness of 0.670 mm, tube voltage of 140 KV, and pixel size of 0.247 mm, resulting in a total of about 250–300 CT slices. The images are then imported into MIMICS (platform for medical image processing) for segmentation and computation. The inner ears are segmented in the following partitions: cochlea, vestibule, lateral semicircular canal, anterior semicircular canal, posterior semicircular canal and common crus (Figure 1). The lengths of every segmented element is calculated on the healthy and on the BPPV side (Table 1) as well the lengths on the common crus: Anterior vestibualr, posterior vestibular and length (Figure 2 and Table 2).Finally the inner ear angulations as seen in Figure 3 is calculated in the same way (Table 3)

Preliminary ResultsAccurate 3D model of the human inner ear is possible with the advanced protocol used in this study. The preliminary results show that the size (mm3) of common crus is greater and coresponds to the side of BPPV in all patients. .

Figure 1: segmentation of human inner ear

Figure 2: Common crus lenghts

Figure 3: Schematic representation for the angulations measurements

PatientsAnterior

semicircular canal

(BPPV)

Anterior semicircular

canal (Healthy)

Posterior semicircular canal (BPPV)

Posterior semicircular

canal(Healthy)

Lateral semicircular

canal (BPPV)

Lateral semicircul

ar canal(Healthy)

Comon crus

(BPPV)

Comon crus

(Healthy)

1 7,71 10,20 9,93 9,98 6,59 9,40 5,41 4,972 20,81 12,74 26,50 15,69 23,38 12,37 9,48 6,503 12,86 14,68 19,08 15,99 12,75 14,81 4,96 4,954 9,96 8,34 15,82 13,10 14,20 8,41 4,88 3,97

PatientsAnterior

vestibular (BPPV)

Anterior vestibular(Healthy)

Posterior vestibular

(BPPV)

Posterior vestibular(Healthy)

Lenght (BPPV)

Lenght (Healthy)

1 2,20 1,86 2,27 1,78 2,25 2,282 2,04 2,30 2,40 2,34 2,78 2,843 2,07 1,84 1,52 1,78 2,15 2,014 2,46 2,19 1,97 2,34 2,32 2,53

BPPV Healthy

Patient 1 133,18 129,71Patient 2 120,79 126,23

Patient 3 115,96 118,32Patient 4 115,86 116,11

Table 1: lenght measurments of semicircular canals and common crus for healthy and BPPV inner ears

Table 2: lenght measurments of common crus for healthy and BPPV inner ears

Table 3: Angulations measurements of common crus for healthy and

BPPV inner ears