Keywords
maxillary nerve block - extraoral approach - neurolytic agent - complication - abducens
nerve palsy
Introduction
Blockade of branches of the trigeminal nerve distal to the Gasserian ganglion is a
well-established procedure in the management of trigeminal neuralgia (TGN). Maxillary
nerve (V2 division) block with alcohol is commonly performed when the maxillary distribution
is predominantly affected. This technique has an acceptable safety profile, and hence
performed as an outpatient procedure. The reported complications of maxillary nerve
blockade are less than 1%, and those described in the literature are dysesthesia,
hypoesthesia, vertigo, and facial swelling. Distant complications, such as ipsilateral
ocular disturbances, are extremely rare and have been described as blurred vision,
amaurosis, mydriasis, miosis, enophthalmos, ophthalmoplegia, and diplopia.[1] These cases have been described in dental practice with intraoral blockade of the
inferior and superior alveolar nerves and have never been described as a potential
sequela in relation to the TGN. Here, we present such a patient who suffered diplopia
and sixth cranial nerve palsy following an extraoral maxillary nerve blockade.
Case Report
A 45-year-old man, a known case of TGN, presented to our pain clinic with complaints
of sharp, lancinating pain over the left side of his face and jaw, corresponding to
the distribution of the maxillary division of the left trigeminal nerve since past
5 years. There was no history of facial injury, dental surgeries, or intraoral infections.
Physical and neurologic examination was unremarkable. Magnetic resonance imaging (MRI)
revealed no evidence of neural compression by a vascular loop. His neuralgia was refractory
to medical management with carbamazepine and pregabalin. Hence, maxillary nerve blockade
was planned at the patient's request on an outpatient basis. His previous medical
history and physical examination were unremarkable. Written informed consent was obtained.
Inside the minor operating room (OR), the standard monitors were attached. Following
sterile preparation and draping of the left side of the face, a 9.0-cm 22G needle
was introduced perpendicularly at the midpoint of the inferior border of the left
zygomatic arch, to hit the lateral pterygoid plate. The needle was then withdrawn
slightly and redirected anteriorly and superiorly. The needle was then carefully advanced
up to 1 cm while stimulating the nerve at 1mA for 0.1 second, until nerve stimulation
was confirmed. After confirmation of negative aspiration, 2 mL of 2% lignocaine was
injected, followed by 1 mL of absolute alcohol. The procedure was uneventful, and
the patient had immediate and profound relief of pain.
A few seconds after the nerve block, the patient complained of discomfort in the ipsilateral
eye and of double vision. On examination, the patient was unable to abduct the left
eye, suggesting a palsy of the left abducens (CN VI) nerve. The eyelid had a slight
droop (ptosis). All other eye movements were normal. There was no noticeable blanching
of skin or numbness of upper face. Subsequent evaluation by a neurologist and an ophthalmologist
was unremarkable, and the patient was reassured and managed conservatively. His symptoms
resolved slowly over a period of 2 months, and the patient reported that his diplopia
had ceased and that his vision had become normal.
Discussion
Similar cases of lateral rectus palsy have been described in dental literature, with
both superior and inferior alveolar nerve blocks.[2]
[3] However, to the best of our knowledge, this complication has not been reported with
extraoral blockade of the maxillary branch of the trigeminal nerve. In this case,
a couple of anatomical reasons may be offered. First, accidental puncture and injection
of anesthetic agents into the middle meningeal artery remains the most likely explanation.
The middle meningeal artery is a branch of the maxillary artery and enters the skull
via the foramen spinosum. It gives off several branches within the middle cranial
fossa, and branches back to the lacrimal and ophthalmic arteries. There is a possibility
of retrograde flow of the anesthetic to the eye when the solution is injected under
pressure, with a reduction in arterial pressure gradient during diastole.[1] Second, accidental intravenous injection of anesthetics may cause flow toward the
cavernous sinus via the pterygoid plexus and emissary veins. The abducens nerve runs
through the cavernous sinus, and the oculomotor, trochlear, and ophthalmic and maxillary
divisions of the trigeminal nerve lie within its lateral wall, which explains the
occurrence of ophthalmological complications.[4] Owing to its location within the cavernous sinus, the abducens nerve may be most
susceptible to the effects of intravascularly deposited anesthetic agents.
Though ophthalmical complications after maxillary nerve blockade are extremely rare,
they are distressing events. Previous articles suggested aspiration prior to deposition
of anesthetic solutions. However, this case shows that such complications are possible
despite all precautions being taken. If the patient reports diplopia, injection should
be stopped immediately and patient examination to be followed. Eye movements, blindness,
facial muscle movement, and blanching of skin should be assessed. The patient should
be reassured that this is a transient event that should resolve as the action of the
anesthetic agent ceases. The patient should be escorted home and advised against driving
until normal sight returns. Ophthalmological and neurological consultations may be
advisable if complications last longer than anticipated. In this case, the complications
lasted for 2 months possibly due to use of absolute alcohol as the neurolytic agent.
To conclude, we reported a case of reversible abducens nerve palsy associated with
extraoral maxillary blockade of the trigeminal nerve. This complication occurred despite
precautions such as aspiration and confirmation of needle tip with stimulation. Knowledge
of such unanticipated complication and its potential cause may help the physician
in planning for an appropriate management protocol.
