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One hundred temporal bones obtained from forensic autopsies were dissected to expose injured structures. Longitudinal fractures were present in 82%, transverse fractures in 11%, and mixed fractures in 7% of the cases. Facial canal injuries were present in almost half of the bones with longitudinal fractures (36/82), although cuts of the facial nerve stem were rarely encountered. Damages to the facial canal associated with longitudinal fractures were most frequently seen in the region of the geniculum. However, transverse fractures with facial canal involvement (7/11) most frequently occurred in the labyrinthine portion, causing a complete cut of the facial nerve. Injuries to the jugular bulb were also common (21/100) and associated with all types of temporal bone fractures. Observed damages to the auditory ossicles included disconnection of their joints or fractures of the malleus or stapes. Fractures of the incus were not observed. Injuries to the carotid canal were common (52/100), although an injury to the arterial wall was observed in only one specimen. The frequency and nature of damage in temporal bone fractures strictly reflect the type of fracture, especially in terms of facial nerve disorders: the most serious damage is observed with fractures that involve the otic capsule.
Temporal bone fractures can adversely affect the quality of life when the vestibulocochlear organ or facial nerve is damaged. Temporal bone fractures are common. Thirty percent of head injuries involve a fracture of the cranial base, and 18% also affect the temporal bone.1 The common causes of temporal bone fractures are road accidents, falls, beatings, and gunshot wounds.2,3,4,5,6
The characteristic direction of the fracture line was used to classify temporal bone fractures as longitudinal, transverse, mixed, and oblique.4,7,8,9,10,11,12,13,14,15 In longitudinal fractures, the fracture line courses parallel to the long axis of the pyramid, through the external auditory canal and tegmen tympani, passes the labyrinthine capsule, and reaches the middle cranial fossa.1,2,3,4,6,7,8,10,11 In transverse fractures, the line of fracture is perpendicular to the long axis of the pyramid or petrous bone,1,4,6,7,9 and its course is variable.
In terms of the labyrinth, two main groups of transverse fractures can be distinguished: internal fractures (anteromedial) and external fractures (posterolateral).16,17 Internal fractures run along the internal auditory canal, traverse the cochlea and geniculate ganglion, and reach the anterior edge of the pyramid. External fractures run through the entire internal ear (the cochlea and vestibule) along the facial canal to the geniculate ganglion. The middle ear, tympanic membrane, and external auditory canal are lateral to the fracture line and typically intact. Structures of the middle and internal ear can be involved with mixed fractures of the temporal bone.18,19 Mixed fractures compose less than 10% of all temporal bone fractures. Longitudinal fractures are regarded as the most common (70 to 90%) followed by transverse fractures (10 to 30%).1,3,12,18,19,20 Sometimes longitudinal fractures occur bilaterally.21 Oblique fractures run across descriptive anatomical planes and are a variant of mixed fractures.4
Damage to the facial nerve is a relatively common complication of temporal bone fractures, resulting in paralysis or paresis (10 to 50%).1,2,3,12,15,16,17,22,23,24,25,26 The pathological damage to the facial nerve can vary. In transverse fractures, the continuity of the facial nerve tends to be lost, while it is rare in longitudinal fractures. Paralysis of the facial nerve associated with longitudinal fractures can also have other causes: a piece of bone impinging on the nerve, pressure exerted on the nerve by a dislocated bone fragment, an intraneural hematoma or nerve contusion.1,22,25 There are other possible serious consequences of temporal bone fractures: a fistula associated with cerebrospinal fluid leakage and the possibility of meningitis,1,2,3,5,27 a traumatic perilymph fistula,28,29 cholesteatoma,16 hearing loss,30,31,32 balance disturbances,16,33,34 and carotid injury.35,36 Data on temporal bone fractures obtained from postmortem observations are sparse. Clinical reports yield only partial information about the temporal bone obtained from computed tomography (CT) and intraoperative observations. We therefore conducted a cadaveric study to characterize temporal bone fractures as fully as possible.
One hundred cadaveric temporal bones obtained from the forensic autopsies of victims of head trauma were examined. Specimens were collected consecutively, without additional criteria of qualification with the exception of data availability (age, mechanism of trauma, management). The age of victims varied between 15 and 87 years (mean 38 years). Damage to the temporal bones was estimated under an operating microscope and standard set of otosurgical instruments. The course of the fracture line was used to classify the injuries as longitudinal, transverse, or mixed.
The studied materials were diverse. They consisted of extremely severe head trauma (including skull defragmentation) and general trauma associated with moderate skull damage. In the latter, the head injury was only one of several injuries and was not the direct cause of death. Thus, the data were analyzed according to the cause of death. In Group I, head trauma was a direct cause of death (62 bones). In Group II, head trauma was one of several injuries encountered during autopsy (38 bones).
In the examined materials, 82 fractures qualified as longitudinal, 11 as transverse, and 7 as mixed. All temporal bone structures could be involved in the fracture line and totally or partially damaged (Table 1). As a rule, longitudinal fractures did not involve the labyrinth, and transverse fractures left the external meatus intact. There were no significant differences in the pattern of the fracture line in the two groups. Therefore, the results for the two groups are presented jointly (Tables 1 and and2).2). The only statistically significant difference between the two groups was the frequency of facial canal fractures (Table 3), which were most frequent in Group I. Theses results are presented separately for both groups (Table 4). Also, see Figures Figures1,1, ,2,2, and and33.
The following structures were involved in longitudinal fractures (Table 1): the osseous portion of the Eustachian tube, external acoustic meatus, tympanic membrane, sigmoid groove, jugular fossa, and the facial and carotid canals. Dislocations of auditory ossicles and their fractures were also common (Table 2). According to the definition, internal ear structures were not involved with longitudinal fractures. In most longitudinal fractures, the tympanic membrane was ruptured, particularly when the external auditory meatus was involved.
Transverse fractures were associated with injuries to the internal, and, sometimes, also to the middle ear structures. Damage to the tympanic membrane or external auditory meatus was not observed, consistent with the definition of this fracture (Table 1). The fracture line was most often located in the anterior part of the labyrinth. Less frequently it ran through its posterior region (semicircular canals). In almost all cases (8/11), transverse fractures were associated with injury to the jugular fossa due to its vicinity to the labyrinth. If the fracture line ran through the oval window, the base of the stapes was also destroyed (Table 2).
Mixed fractures involving the structures of the middle, inner, and external ears reflected the combined features of longitudinal and transverse fractures. Damage to the auditory ossicles produced dislocated joints, fractures, or both (Table 2). Interestingly, fractures of the incus were not observed. The fracture line in the malleus ran through its neck and seldom through its head. Fractures of the stapes involved both its branches or its plate. Fractures of the facial canal were common and localized in the various topographical segments of the canal.
Most fracture lines did not run in a perpendicular plane; rather they tended to run more or less obliquely. This finding is consistent with other researchers’ observations that oblique fractures are the most common.4,8 In our opinion, however, the course of a fracture plane described as oblique does not contradict the classification of fractures as longitudinal, transversal, or mixed types, as introduced by Ulrich.7 First, this classification is based on the three main parts of the ear, not on the geometry of the fracture plane, and has considerable clinical merit. As defined, longitudinal fractures avoid the labyrinthine structures, while transverse ones include them; mixed fractures run through both regions of the ear.1,16,17
Fractures of the sigmoid groove, jugular fossa, or both were common injuries (2/5 of all studied fractures). Their frequency was highest in transverse fractures (Table 1). In all cases sigmoid groove or jugular fossa fractures were accompanied by interruption of the walls of the adjacent veins. This finding is consistent with clinical observations that fractures of the temporal bone may manifest with massive venous hemorrhage.3,6,10,11,16 However, fractures of the carotid canal, which were also often observed (half of all studied bones) were rarely associated with injury to the arterial wall (1 case, transverse fracture). This finding is consistent with some clinical observations, but CT, magnetic resonance imaging, and angiographic data suggest that small angiographic abnormalities due to carotid canal fracture are common.35,36
The tympanic membrane was injured in longitudinal and mixed fractures. When the fracture line did not include the external acoustic meatus, the membrane was intact, as occurred in 28 of 82 longitudinal fractures (34%) and in 4 of 7 mixed fractures. Clinically, it is observed as a hemotympanum phenomenon. Our findings comply with Tos's data that the frequency of this phenomenon is about 40%.6 In these cases, the fracture passed through the mastoid process and often through the sigmoid sinus.
The facial canal was injured in almost all mixed fractures (6/7), in almost half of the longitudinal ones (36/82), and in more than half of the transversal fractures (7/11) (Table 2). Therefore, in our material, the facial canal was injured in 49 of 100 fractures, although 20 fractures were associated with sectioning of the facial nerve (20% of fractures, 40% of fractures with facial canal involvement).
Data available in the literature indicate that the mean frequency of facial nerve dysfunction associated with pyramid fractures is about 16%. However, this percentage depends on the type of fracture. In longitudinal fractures, facial nerve paralysis is observed in 10 to 18% of cases (about 25% associated with the loss of facial nerve continuity) and in 38 to 50% of transverse fractures (100% with a cut nerve stem).1,3,6,17,22,23,24,25,26
In the 82 longitudinal fractures observed in our material, the facial canal was injured in 36 cases (44%), and continuity of the facial nerve was lost in 6 of these 36 cases (7.3%). The facial canal was involved in 63% of the transverse fractures, all of which were associated with a severed nerve stem. Longitudinal fractures in Group II (multiorgan damage, head trauma not the main cause of death) were associated with injury to the facial canal in 6 of 31 cases (19%), and a complete cut of the facial nerve was observed in 1 of 6 cases (17%). In transverse and mixed fractures, the differences between Groups I and II failed to reach statistical significance.
In our longitudinal fractures, the facial canal was injured only in the genu region or its mastoid portion. Based on the literature, the fracture line in relation to the facial canal in longitudinal fractures is located as follows: 4% in the labyrinthine segment, 64% in the tympanic segment, 25% in the genu region, and 7% in the mastoid segment. Meanwhile, in transverse fractures, the fracture line runs through the facial canal in the meatal segment in 10% of cases, in the labyrinthine segment in 80%, and in the genu region in 10%.22 Our data support other authors’ observations that most facial canal injuries (80 to 93%) involve the genu region.1,15,17,21,22,23,24,25
According to the literature, fractures of the facial canal localized in the labyrinth or tympanic segment always interrupt continuity of the nerve, which is consistent with our findings (Table 3). In contrast to clinical reports, we observed no involvement of the tympanic region of the facial canal with longitudinal fractures.15,21,22,25 Injuries to the mastoid region were relatively uncommon (7% of cases with facial canal damage), consistent with other authors’ data.1,22,23,25 According to many authors, transverse fractures are associated with the highest frequency of facial canal injuries. In contrast, in our study there was no significant difference in the frequency of these injuries associated with either longitudinal or transverse fractures. This finding probably reflects the high number of injuries in the genu region associated with longitudinal fractures, which may not have clinical manifestations. This observation seems to be particularly useful from a clinical perspective, justifying full exploration of the facial canal (up to the genu region) in decompression procedures.
Fractures of the sigmoid groove and/or jugular fossa, quite often injuries, always interrupt the walls of these vessels. Fractures of the carotid canal, although also frequent, seldom lead to the break of arterial wall. Thus, almost all serious ear hemorrhage is of venous origin. The facial canal in the genu region is the most common location for injury. In transverse fractures, the nerve trunk is interrupted; in longitudinal and mixed fractures, the continuity of the facial nerve trunk may be preserved.
Dr. Wysocki presents a well-done, careful, and systematic microanatomical study on 100 consecutive temporal bone fractures associated with fatal head injury. Autopsy studies with these kind of numbers are becoming increasingly rare, particularly in the United States, yet a tremendous amount of information can come from them. This study is a good example.
He found that 82% of fractures were longitudinal, 11% transverse, and 7% mixed, which is not unexpected. He found a surprising incidence of facial canal disruption (37%) associated with longitudinal fractures, but nerve disruption occurred in only 7% versus 63% of cases of transverse fracture. He also noted a surprising incidence of ossicular disruption, fracture, or both, as well as jugular bulb injury. Both of these latter findings seem significantly higher than clinical experience would suggest and may reflect the severity of temporal bone fractures associated with fatal head injury, as opposed to basilar skull fractures associated with lesser degrees of survivable closed head injury.
The incidence of carotid canal fracture (52%) is very interesting given Dr. Wysocki's finding of carotid artery injury in only 1 case. Clinical experience suggests that angiographic abnormalities will be present in 42% of cases studied for the presence of a basal skull fracture involving the carotid canal,1 and as many as 18% of patients with carotid canal fractures may develop clinically symptomatic vascular complications.2 The likely explanation for this discrepancy is that basal skull fractures through the carotid canal probably lead to intimal dissection as the most common injury, subsequently resulting in thrombosis or embolization rather than transmural disruption. I suspect that Dr. Wysocki's autopsy studies are less sensitive to detecting intimal injury as opposed to transmural disruption through the adventitia. From a clinical standpoint, we need to maintain heightened vigilance for vascular sequelae when carotid canal fractures are identified. Whether or not routine further screening (angiography, computed tomography angiography, magnetic resonance angiography) is a cost-effective approach remains the subject of ongoing debate.1,3