Research Article: The potential protective effects of temporal bone pneumatization: A shock absorber in temporal bone fracture

Date Published: May 31, 2019

Publisher: Public Library of Science

Author(s): Tae Kyu Kang, Ryun Ha, Jae Hwan Oh, Woongsang Sunwoo, Suresh Agarwal.

http://doi.org/10.1371/journal.pone.0217682

Abstract

We hypothesize that when temporal bone fractures occur, the pneumatic cells in the temporal bone are able to absorb most of the impact force during a traumatic event. This study aims to correlate the degree of pneumatization of the temporal bone with the severity of temporal bone fracture (TBF).

Charts and computed tomography scans representing 54 TBFs, diagnosed from 2012 to 2017 at a single tertiary hospital, were retrospectively reviewed. Temporal bone pneumatization (TBP) in the petrous apex and mastoid region was evaluated using previously published classification systems. TBP classifications and fracture types were correlated with TBF complications such as sensorineural hearing loss (SNHL), facial nerve palsy (FNP), and vestibular dysfunction.

Patients with increased pneumatization of the temporal bone had significantly fewer and less severe SNHL. SNHL more strongly correlated with the degree of pneumatization in the mastoid (P = 0.005) than that in the petrous apex (P = 0.024). On the other hand, the degree of TBP correlated poorly with FNP and vestibular dysfunction. However, the mastoid hypopneumatization demonstrated significant correlation with otic-capsule violations (P = 0.002). Fractures with otic-capsule violation were 4 times more likely to have vestibular dysfunction (P = 0.043) and 3 times more likely to have SNHL (P = 0.006). FNP was not associated with otic-capsule violating fractures but was 3.5 times more common in comminuted fractures (P = 0.025).

The degree of temporal bone pneumatization was negatively correlated to the incidence of otic-capsule violation and the severity of hearing impairment in patients with temporal bone fracture. This study substantiated the potential protective effect of temporal bone pneumatization in TBFs.

Partial Text

In humans, temporal bone pneumatization (TBP) begins during prenatal development [1]. Pneumatization refers to both the process by which the epithelium expands into developing bone and the resulting interconnected air cells within the temporal bone [2]. Only humans and primates have pneumatized spaces such as the mastoid air-cell system in temporal bones [3]. Studies suggested that the extent of pneumatization has decreased over the course of human evolution and usually limited to the mastoid, the petrous apex, and the perilabyrinthine regions in human temporal bones [4]. However, little is known about the evolutionary value and/or functional significance of these pneumatized spaces. While the function of TBP remains unknown, numerous previous studies reported the correlations between the degree of TBP and various pathologies including atelectasis, otitis media, and cholesteatoma [5–9]. Generally, poor pneumatization in temporal bone is closely associated with increased incidence and poor prognosis of these pathologic conditions. To explain this relationship, people have long debated the function of TBP and a number of theories have been proposed: 1) pressure buffer, 2) gas reserve, and 3) shock absorption spaces.

This retrospective study was approved by the institutional review board of the Clinical Research Institute at Gachon University Gil Medical Center (No. GFIRB2019-065). All methods employed in this study were in accordance with the approved guidelines and the Declaration of Helsinki. Data were collected from an electronic medical records database and analyzed anonymously. All clinical data were retrospectively reviewed by two otologists.

A total of 49 patients were included in this study. The mean age was 47.9 years (22–74), and most patients were male (n = 41, 83.7%). Falls were the most common mechanism of injury, present in 53.1% (n = 26) of cases. It is notable that motor vehicle accidents (MVAs) accounted for 36.7% (n = 18) of cases. Among 18 cases of MVA, 7 were motorcycle riders, 10 were pedestrians, and only 1 patient was a car passenger. Blunt assaults and heavy object falling were responsible for 4.1% (n = 2) and 6.1% (n = 3) of cases respectively.

To our knowledge, this is the first study to report a direct correlation between the degree of TBP and the severity of clinical sequelae associated with TBF in a large group of adult patients. The patients are predominantly male (83.7%), and injury by falls (53.1%) is the most common. Our findings indicate that the degree of TBP showed a significant association with functional deficits from injury to structures within temporal bone. OCV fractures were present only in temporal bones with reduced pneumatization. In OCV fractures, persistent SNHL, including 40% with mild to moderate (26–60 dB) and 60% with severe to profound (>60 dB), and vestibular dysfunction (60%) were more frequently found. The greater the degree of pneumatization tended to have the less the possibility of SNHL and the less the degree of SNHL. However, facial nerve injury after TBF was less likely to have correlation with the degree of TBP. This is likely the result of a long, complex, and tortuous intraosseous course of the facial nerve, given the potential for injury in any part of the pathway from high energy trauma. Our results supported the hypothesis that TBP acts as a shock absorber to protect surrounding vital structures in trauma.

In this study, the correlation between the degree of pneumatization and clinical sequalae from temporal bone fracture was investigated. The degree of pneumatization in the temporal bone was negatively correlated to the incidence of OCV fracture and the severity of hearing impairment in patients with temporal bone fracture. This study substantiated the potential protective effect of temporal bone pneumatization in TBFs.

 

Source:

http://doi.org/10.1371/journal.pone.0217682

 

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