Pneumatization of the temporal bone, its petromastoid part and related vasculature in a South African population from early childhood to early adulthood: an anatomical and radiological study.

Abstract

Introduction: The pneumatization of the temporal bone is important in various clinical settings. These include serving as a prognostic factor in middle ear surgeries and acting as a shock absorber in patients sustaining lateral skull trauma. The size and growth rate of its air cell system have been associated with middle-ear pathology. The degree of temporal bone pneumatization is highly relevant when planning temporal bone-related surgeries and has been hypothesized to influence anatomical variations of temporal bone-related vessels. This study aimed to investigate the size of temporal bone pneumatization (air cell volume) with age, the association between temporal bone pneumatization and the morphologies of some temporal bone-related vessels, as well as their morphometrical relationship with ear regions, and to propose a simple and concise classification of the degree of temporal bone pneumatization using reference structures and landmarks. Materials and Methods: A retrospective review of 496 temporal bone computed tomography (CT) images of 248 head and neck/brain CTs of patients from public hospitals in KwaZulu-Natal, South Africa, was conducted. The sample consisted of 133 males and 115 females, 0 to 35 years old (median age 13.0 years) of three population groups (202 South African Black, 28 South African Indian, and 18 South African White). The age range of 0 to 35 years was further divided as follows: 0-2 (infant); 3-5 (young child); 6-9 (middle child); 10-14 (early adolescent); 15-18 (middle adolescent); 19-25 (young adult stage I); 26-35 (young adult stage II). High-resolution CT images with fine slices of ≤ 0.625 mm were analyzed using IntelliSpace Portal (ISP) Version 11.1 viewer software. The volume of temporal bone pneumatization was achieved using three dimensional (3D) volumetric rendering technique. At the same time, the morphologies of the sigmoid sinus, jugular bulb, and internal carotid artery and their morphometrical relationships with ear regions were analyzed using the measuring tools on the ISP. Additionally, an inter-observer assessment was conducted among otologists to classify the degree of temporal bone pneumatization utilizing temporal bone CT images at two levels (landmarks): the malleoincudal junction and the lateral semicircular canal using sigmoid sinus as a reference. Results: Size (volume) of temporal bone pneumatization with age: The volume of temporal bone pneumatization increased significantly (p<0.001) with age up to the adult stage I (19-25 years), followed by a significant decline in young adult stage II (26-35 years). Females showed a significant early increase compared to males. Regarding population groups, Black South Africans (SA) showed a higher increase in volume with age than the SA Whites and Indian population groups. xiv Influence of pneumatization on temporal bone-related vessels: Four degrees of pneumatization (hypo, moderate, good, and hyper) were analyzed. Hyper-pneumatization was observed to be more common. Vascular variants such as high jugular bulb, jugular bulb dehiscence, and internal carotid artery dehiscence were observed and significantly associated (p<0.01) with hyper-pneumatization. Also, as pneumatization increases, sigmoid sinus and jugular bulb distances to ear regions were observed to increase significantly (p<0.01, p<0.05). The sigmoid sinus and its variant shapes were also observed but were not significantly associated with the degrees of pneumatization (right- p= 0.070; left- p= 0.645). Classification of degree of pneumatization: In the survey conducted among cohort otologists, the percentage of participants that correctly rated temporal bone CT images taken at the level of lateral semicircular canal according to their respective degrees of pneumatization was significantly higher (p < 0.05) regardless of their year of experience compared to those that correctly rated corresponding images taken at the level of malleoincudal junction. A 76% positivity in their agreement with the use of sigmoid sinus in evaluating mastoid pneumatization was observed. Discussion and Conclusion: This study concludes that the pneumatization of a healthy temporal bone is expected to show a significant linear increase from infant up until at least the early adult stage I (19-25 years) in the South African population. The high incidence of high JB, JB dehiscence, and internal carotid artery dehiscence, and the increase in distances of sigmoid sinus and JB to ear regions reported in this study population due to increased pneumatization validates temporal bone pneumatization as a factor that influences jugular bulb variants and internal carotid artery dehiscence as well as the distances of sigmoid sinus and jugular bulb to ear regions. The study also concludes that using the lateral semicircular canal as a landmark on axial CT, and evaluating air cells around the sigmoid sinus was suitable in classifying the degree of temporal bone pneumatization into hypo-, moderate, good, and hyper-pneumatization. This study proposes this classification system as an easier and quicker method for clinical applications.