Morphometric Analysis of Internal Acoustic Meatus

 

Prashaanthi. N¹, Karpagam Krishnamoorthy²

¹I year BDS, Saveetha Dental College, Chennai, India

²Senior Lecturer, Department of Anatomy, Saveetha Dental College, Chennai, India

 

ABSTRACT:

Aim and objective : To study the morphometric analysis of internal acoustic meatus . Background: The internal acoustic meatus (iam) is a short bony canal that lies between the posterior surface of the petrous pyramid and the bony labyrinth within the dense petrous part of the temporal bone. The cn vii ( facial nerve ), cn vii ( vestibulotrochlear nerve ) and labyrinth vessels pass through the internal acoustic meatus. The internal acoustic meatus is important as a region in which acoustic neuromas occur.

 

 

 

INTRODUCTION :

The internal acoustic canal (IAC), also known as the internal auditory canal or meatus (IAM), is a bony canal within the petrous portion of the temporal bone that transmits nerves and vessels from within the posterior cranial fossa to the auditory and vestibular apparatus. The VII and VIII cranial nerves namely facial nerve and vestibulotrochlear nerve and labyrinth vessels pass  through the internal acoustic meatus. This canal has been clinically important as a region in which acoustic neuromas occur. [1]

 

Quantitative and morphometric assessment of the internal auditory canal (IAC) are essential to establish the anatomical bases for microsurgery of the cerebell-opontine angle and acoustic neuroma, which may produce bone changes and is an important intracranial pathology.[2]

 

The required diameter for the neurovascular bundle running through the internal auditory canal is about 2 mm. Therefore, a stenosis of 2 mm or less is regarded as significant.

 

Possible reasons for acquired uni- or bilateral IAC enlargement are tumors originating in the IAC such as uni- or bilateral acoustic neuroma or, much less commonly, advanced facial neuroma. [3]

 

MATERIAL AND METHODS:

31 human cut skulls obtained from Indian cadavers were studied. Using vernier callipers the following 2 measurements with an accuracy of 0.1 mm was measured.

 

Height of the middle portion of IAM: vertical diameter of IAM at the middle portion of the meatus. Width of the middle portion of IAM: horizontal diameter of IAM at the middle portion of themeatus.           

 

All the measurements were done by the same person. The data was analysed by SPSS software and the attained data was extracted in statistical tables.

 

 

 

RESULT:

Morphometric analysis of internal acoustic meatus
S.No	Height of the middle portion of IAM (Right )	Width of the middle portion of IAM ( Right)	Height of the middle portion of IAM ( Left)	Width of the middle portion of IAM ( Left )
1	4	6	4	6
2	5	4	5	4
3	4	7	4	7
4	3	5	3	7
5	4	5	4	6
6	4	6	3	6
7	3	6	3	7
8	3	6	3	7
9	4	7	4	7
10	4	8	3	10
11	4	9	4	8
12	3	7	3	8
13	4	6	4	7
14	4	6	5	8
15	5	7	4	6
16	3	10	3	9
17	4	8	5	9
18	3	6	3	8
19	3	8	2	7
20	4	6	3	6
21	4	1	4	10
22	4	6	4	6
23	4	8	4	8
24	3	7	3	7
25	4	6	4	6
26	3	5	3	6
27	5	7	4	5
28	4	6	3	6
29	5	7	5	7
30	3	5	3	5
31	4	6	5	6
Range	3-5	1-10	2-5	4-10
Mean	3.8	6.4	3.6	6.9

 

DISCUSSION:

The structure and anthropometry of internal acoustic meatus has been studied. Moeller (2000) in his book “Normal findings in radiology” reckoned the width and length of IAM 5mm (2-12mm) and 8mm (4-25mm), respectively. Sakashita and Sando in their paper in 1995, described the anthropometry of IAM in addition to its 3D structure. They found the height and width of the middle portion of IAM 4.8mm (3.2-6.5mm) and 4.9mm (3.1-7mm)[1] compared to our study.

 

In our study the range of the height of the internal acoustic meatus is 3-5 mm ( right) and the width of the internal acoustic meatus is 1-10 mm ( right ) . The range of the height of the internal acoustic meatus is 2-5 mm (left ) and the width of the internal acoustic meatus is 4-10mm ( left ). The mean value of the height of the right internal acoustic meatus is 3.8mm and the width of the right internal acoustic meatus is 6.4mm. The mean value of the height of the left internal acoustic meatus is 3.6mm and the width of the left internal acoustic meatus is 6.9mm

 

CONCLUSION:

This study provides basis for evaluation of the internal acoustic meatus for pre surgical operations and also for the congenital anomalies of the internal acoustic meatus. The meatus transmits the facial nerve and the vestibulocochlear nerve along with the labyrinthine vessels. These structures are vital and thorough knowledge of the anthropometry of the meatus plays a main role in any surgical procedure. This study also helps to know any congenital anomalies or variations in the structure of the internal acoustic meatus if seen and accordingly surgical procedures can be planned.

 

REFERENCES:

1.     Reza Masteri Farahani, Mehrdad Nooranipour and Kamran Vafaei Nikakhtar.  Anthropometry of Internal Acoustic Meatus, Int. J. Morphol., 25(4): 861 - 865, 2007.

2.     Sergio Ricardo Marques, Sergio Ajzen, Giuseppe D Ippolito, Luis Alonso, Sadao Isotani, Henrique Lederman, Morphometric Analysis of the Internal Auditory Canal byComputed Tomography Imaging, Iran J Radiol. 2012;9(2) :71-8. DOI: 10.5812 /iranjradiol. 7849.

3.     H. Stimmer, H. P. Niedermeyer, V. Kehl, E. J. Rummeny, Nontumorous Enlargement of the Internal Auditory Canal: A Risk Factor for Sensorineural Hearing Loss? A High Resolution CT-Study , Stimmer H et al. Nontumorous Enlargement of Fortschr Röntgenstr 2015 ; 187: 450–458.

 

 

Accepted on 01.07.2016           © RJPT All right reserved

Research J. Pharm. and Tech 2016; 9(10):1575-1576.