Role of Multislice Computed Tomography with 3D Imaging in Diagnosis of Temporal Bone Lesions 111
Citation: Role of Multislice Computed Tomography with 3D Imaging in Diagnosis of Temporal Bone Lesions. American Research Journal of Radiology and Nuclear Medicine; 1(1): 13-23.
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Introduction: MSCT is presently the most accurate technique to study the temporal bone anatomy or pathology.
Objective: To evaluate the utility of MSCT imaging with 3D reconstruction in assessment of temporal bone lesions Patients & Methods: This study included 100 patients (46 males & 54 females) their age ranged from 1:73 years. They had variable problems; hearing loss, vertigo, tinnitus, suspected otitis media, congenital malformation, trauma, inflammatory or neoplastic lesions. MSCT with 3D reconstruction was done for all patients. 3D reconstruction done using MIP & VR techniques.
Results: Our study included 11 patients with external ear pathology (5 patients with otitis externa, 4 patients with osteochondroma & 2 patients with external ear deformity). 40 patients with middle ear pathology (25 with otitis media & 15 with cholesteatoma), inner ear pathology in 5 patients (2 congenital, 3 post cochlear implant) and 18 patients had other variable pathology; 8 patients with trauma however only 4 patients had fractures, 2 patients with jugular dehiscence, 2 patients with jugular bulb ectasia, 1patient with petrous apex cyst, 2 patients with mastoid fibrous dysplasia, 2 patients with Dermoid cyst and the last patient with meningioma enplaque showing squamous bone thickening.
Conclusion: MSCT 3D reconstructed images played an important role in assessment of the anatomical details of small middle ear and inner ear structures pathological changes; however it needs much familiarity with the 2D anatomy and caution in post processing to avoid false results and artifacts. Further studies for specific pathology will be more beneficial than evaluation of variant pathology.
Keywords: Multi-slice CT (MSCT), 3D, temporal bone
The temporal bone is a complex structure with five developmentally different regions and multiple variable pathological lesions. Multislice computed tomography (MSCT) is presently the most accurate technique to study the temporal bone anatomy or pathology as it offers excellent delineation of the ear. It can show bony walls of the external and middle ear, the bony labyrinth, the bony facial nerve canal, the bony internal auditory canal.1
Recent developments in CT software technology have made it possible to rapidly generate the three-dimensional (3D) and multiplanar reformatted (MPR) images from conventional (2D) cross-sectional computed tomographic (CT) data.2 The additional information provided by 3D reconstructed images allows a better understanding of temporal bone complex anatomy containing multiple small structures and improves the ability to evaluate related disease, in addition it helps much to optimize adequate surgical planning.3
The aim of this study directed to: Evaluate the utility of Multislice CT imaging with 3D reconstruction in assessment of various temporal bone lesions
PATIENTS AND METHODS
Our prospective study included 100 patients (46 males and 54 females), their age ranges from 1 to 73 years who had temporal bone problems like hearing loss, vertigo, tinnitus, suspected otitis media, congenital malformation, post traumatic fracture, inflammatory or neoplastic lesions. The study was done at security forces hospital, Makkah, where the patients were referred from ENT clinics to the radiology department, from January 2015 till December 2016, with no age or sex predilection. The study was approved from the ethical committee and a written consent was taken from each patient included in the study. MSCT examination carried in using SOMATOM Definition AS (64 detector) Multislice CT machine, Siemens/Germany (2012). All patients were subjected to history taking and full clinical examination. MSCT scan with 3D reconstruction images were done for all patients. 3D reconstruction was done using MIP and VR techniques.
Examination procedure explained to the patient or to the relatives of the young patient or child in order to obtain his/her cooperation. Removal of any metallic objects at head and neck to avoid image artifact. Patient placed in a symmetrical supine position (head first using head rest), with flexion or extension of the neck to limit irradiation of the lens to a minimum.
Image Acquisition and Scanning Parameters
The studies were performed with the following parameters: 0.75 mm collimation, 1mm section thickness, 120 kVp, 240 mAs, pitch of 0.6, rotation time 0.75 sec, 15 cm field of view, filter bone, and a 512 x 512 matrix. The initial data sets were then reconstructed at 0.6 mm slice thickness. The axial scan was done with the patient in supine position and the gantry tilted 0 while the scanning plan was parallel to the orbito-meatal line. Images were started inferiorly below the lower margin of external auditory meatus. Nonionic water soluble contrast media (Visipaque 320 mgI/ml) was used in 5 patients with suspected soft tissue lesions and intra-cranial extension.
Image Processing and Reconstruction
In our study, post processing and reconstructions methods included 2D MPR for routine reconstruction while MIP and VR techniques were used for 3D reconstruction.
Multiplanar Image Reconstruction (MPR)
Had done in 3 different planes, axial, coronal and sagittal planes. Axial images reconstructed parallel to the lateral semicircular canal. Coronal plane images perpendicular on TMJ while sagittal images done with the longitudinal axis parallel to the longitudinal petrous axis giving sagittal oblique images that clarify the small tiny structure of the middle and inner ear.
Three-Dimensional (3D) Image Reconstruction
By using maximum intensity projection (MIP) and volume rendering (VR) methods we were able to create 3D images especially of the small structure of the middle and inner ear.
Maximum Intensity Projection (MIP)
This technique displays the pixels of greatest intensity along a predefined axis of the image. During the processing of the image data there were two types of MIP, the ordinary MIP and thin MIP.
Ordinary (Thick) MIP, by selecting thick MIP the details of the small structure like ossicels and inner ear structure is not clear, however by selecting Thin MIP, utilization of the images related to area of interest results in delineation of small structures and their details. Also we can separate small structure like ossicels or cochlea from the other bones by cutting and removing the surrounding bones guided by other 2D MPR images.
Volume Rendering (VR)
The technique interpolates the entire data set rather than editing a single scan to generate 3D images directly from scanned volume data. In our study concerning the temporal bone, we have chosen the musculoskeletal bone window. After zooming and removing other parts of the skull bones, we achieved selected 3D images of the temporal bone specially its petrous part, however the details of the small structures were unclear.
Thin Volume Rendering (VR)
Method provided us with 3D volumetric image. The images were so demonstrative and the anatomic details of small structures were clear. Also using the different window options of VR, we found that the transparent window is very good in delineation of the middle ear ossicels and inner ear structures.
This study included 100 patientshad problems related to the temporal bone like hearingloss, vertigo, tinnitus, suspected otitis media, congenital malformation, post traumatic fracture, inflammatory or neoplastic lesions. They were 46 male and 54 female with age range from 1 to 73 years (mean age about 47). Although there was a wide range of age, it has no significance as the study was not directed to a specific temporal bone pathology or sex or age predilection.
In our study; the most common symptom was hearing loss followed by discharge and tinnitus (table1). However, there were two patients with different complaint not related to the temporal bone; one had proptosis and diminution of vision and the other had epilepsy. Both patients after doing CT we found pathology related to the temporal bone (meningioma en-plaque and petrous apex cyst consequently)
The commonest provisional clinical diagnosis of the patients was the hearing loss (31 patients had SNHL and 30 patients had CHL) followed by otitis media and the least diagnosis was external ear deformity in two patients (table 1). MSCT had been done for all patients included with the findings broadly classified according to the region of the pathology that correlated to the clinical symptoms in almost of the cases (table 2).
Regarding the MSCT findings, external ear pathology detected in 11 patients (11%), middle ear pathology in 40 patients (40%), 31 patients (31%), with inner ear symptoms but positive findings only in 5 patients (5%) and 18 patients (18%) with variable pathological lesions. On the other hand, 31 patients (31%) had normal CT findings although they had symptoms related to temporal bone, 26 had SNHL and the remaining 4 patients had history of trauma related to temporal bone however no fracture was detected.
For the external ear, there were 5 patients (5 out of 11 patients, 45.4%) with otitis externa, 4 patients (4 out of 11 patients, 36.4%) with osteochondroma and 2 patients (2 out of 11 patients, 18.2%) with external ear deformity that being atresia of the external auditory canal and small accessory auricle with normal external auditory canal. (Table 2) In cases of middle ear pathology were 25 (25 out of 40 patients, 62.5%) with otitis For the external ear, there were 5 patients (5 out of 11 patients, 45.4%) with otitis externa, 4 patients (4 out of 11 patients, 36.4%) with osteochondroma and 2 patients (2 out of 11 patients, 18.2%) with external ear deformity that being atresia of the external auditory canal and small accessory auricle with normal external auditory canal. (Table 2) In cases of middle ear pathology were 25 (25 out of 40 patients, 62.5%) with otitis.
As regard the external ear, Dubach and Häusler4 statedthat simple otitis externa is a common disease of the external auditory canal and characterized by diffuse thickening and edema of its wall. The previous mentioned findings matches with our current study as 11% of the patients included had external ear pathology, 45.45% of them had simple otitis externa with the most common findings was diffuse thickening and edema of mucosal lining of the external auditory canal however no evidence of extension to TMJ or associated bone erosion or destruction as a differentiating point for external ear cholesteatoma.