Keywords
bilateral facial palsy - fracture - temporal bone
Introduction
The temporal bone is a complex bone encapsulating many vital structures. Fracture
of the temporal bone, especially when it violates the otic capsule, tend to injure
facial nerve more than the fractures that spare the otic capsule. Most fractures of
the temporal bone are unilateral and otic capsule sparing. Bilateral temporal bone
fracture with facial nerve injury is a rarity. Involvement of both facial nerves augments
the diagnostic and therapeutic challenges involved.
Case Report
A 27-year-old man was referred with the inability to close both the eyes completely
from the neurosurgical department. It followed a road traffic accident 10 days prior,
resulting in closed head injury and intracranial bleeding, which was managed with
appropriate neurosurgical intervention. Physical examination revealed an expressionless
countenance and complete immobility of all facial muscles with House–Brackmann grading
of 6/6. On closure of the eyes, Bell's phenomenon was observed on both sides ([Fig. 1]). Otoscopy revealed bilateral hemotympanum, but showed no evidence of injury of
external auditory canal or cerebrospinal fluidotorrhea.
Fig. 1 Bell's phenomenon and masklike expression in bilateral facial nerve palsy.
Audiological evaluation confirmed bilateral conductive hearing loss and bilateral
flat type B curve in tympanometry. Electroneuronography (ENoG) showed reduction in
amplitude of the waveform on both sides on maximal stimulation. High-resolution computed
tomography scan of the temporal bone revealed symmetrical longitudinal fractures coursing
through the petrous part, sparing the otic capsules but extending cranially to the
squamous part. On the both sides, the fracture line crossed the region of the geniculate
ganglia of the seventh cranial nerve ([Fig. 2]). Additionally, hemorrhagic contusions were observed on both temporal and parietal
lobes, with focal subarachnoid hemorrhage over the right temporal lobe.
Fig. 2 Symmetrical bilateral temporal bone fractures involving the geniculate ganglion.
The patient underwent surgical intervention of both sides on the 12th day after onset.
On the right side, facial nerve transection was observed on the proximal part of the
horizontal segment adjoining the geniculate ganglion. A short segment of greater auricular
nerve was used for neural grafting. Limited access to the proximal end of the transsection
prevented the graft from being secured with sutures to the nerve. The grafted segment
was therefore wrapped around in temporalis facia and stabilized with fibrin glue.
On the left side, there was no discontinuity of the nerve, but nerve sheath was edematous
in the horizontal segment, which was duly decompressed. Follow-up 6 months after surgery
revealed House–Brackmann grading of 5/6 on the left side and 3/6 on the right side.
Discussion
Bilateral facial nerve palsy, defined as involvement of both hemifacies within 4 weeks
of onset, is a rare condition occurring in 0.4% of all cases of facial nerve palsy.[1] The commonest cause, Bell's palsy, is a diagnosis arrived by exclusion of traumatic,
metabolic, immunological, infective, and vascular causes.[2] Fractures of skull base occur in 4 to 30% of closed head injuries due to falls,
assault, or traffic accidents, with temporal bones involved in 22%.[3] These fractures are mostly unilateral, with bilateral fractures reported in less
than 20%. Of these, bilateral facial nerve palsy is limited to a mere 3%.[4]
Conventionally temporal bone fractures are described as longitudinal or transverse
based on its alignment to the axes of the temporal bone. However, descriptors such
as oblique fractures have been added to describe a fracture plane that crosses the
petrotympanic fissure.[5] Longitudinal fractures are most likely to involve the fallopian canal in the region
of the geniculum, whereas labyrinthine segment is the usual site of injury in transverse
fractures. Transection of the nerve is more common in transverse fractures.[6] These morphological descriptions of the fractures do not accurately correlate with
the clinical sequelae. Involvement of the otic capsule is a more accurate predictor
of the outcome. Facial nerve injury is twice as common when the otic capsule is violated.[7] High-resolution imaging of the temporal bone plays a crucial role in accurately
identifying the site of injury. However, assessing the severity of damage with certainty,
especially when a transection of the nerve is suspected, is often difficult radiologically.
Electrophysiological tests such as ENoG have the potential to assess the severity
of neuronal damage and degeneration with precision. When done serially in the window
period between 3 and 21 days after onset, it determines the threshold for surgical
intervention when 90% or more of neuronal degeneration is recorded. However, use of
ENoG is compromised in bilateral facial nerve palsy as ENoG can only determine the
degree of neuronal degeneration when the evoked amplitude of the traumatized side
is compared with that of the unaffected side in unilateral facial nerve palsy.
Therefore, in posttraumatic bilateral facial nerve paralysis, decision on the necessity
of surgical intervention and its timing is primarily based on the immediacy of onset
and completeness of palsy. Immediate complete palsy indicates loss of neural discontinuity,
whereas delayed onset or partial palsy suggests an intact nerve compromised by neural
edema and/or hematoma in the fallopian canal compressing the nerve. Often, an early
diagnosis of bilateral facial nerve palsy secondary to head injury is delayed as the
nerve function cannot be checked in an unresponsive comatose patient. A masklike facial
expression with lack of asymmetry of the face on volitional movement adds to the diagnostic
dilemma.[8] Surgical intervention also tend to get delayed due to unfavorable posttraumatic
neurologic status. However, inappropriate delay should not be the aver surgical intervention
as studies suggest reasonable recovery even in surgical intervention performed as
late as 160 days.[9]
[10]
Conclusion
Bilateral temporal bone fracture with bilateral facial nerve palsy is a rare entity.
Clinical diagnosis of this condition is often delayed in a neurologically compromised
patient. High-resolution imaging accurately identifies the site of facial nerve injury
but not the severity of the injury. ENoG, a useful tool for assessing neuronal degeneration
in unilateral facial nerve palsy, is not feasible in bilateral involvement of facial
nerve. Immediate surgical intervention is warranted when there is immediate, complete
posttraumatic facial nerve palsy.
