Cranial nerve injury after Le Fort I osteotomy

Abstract

A Le Fort I osteotomy is widely used to correct dentofacial deformity because it is a safe and reliable surgical method. Although rare, various complications have been reported in relation to pterygomaxillary separation. Cranial nerve damage is one of the serious complications that can occur after Le Fort I osteotomy. In this report, a 19-year-old man with unilateral cleft lip and palate underwent surgery to correct maxillary hypoplasia, asymmetry and mandibular prognathism. After the Le Fort I maxillary osteotomy, the patient showed multiple cranial nerve damage; an impairment of outward movement of the eye (abducens nerve), decreased vision (optic nerve), and paraesthesia of the frontal and upper cheek area (ophthalmic and maxillary nerve). The damage to the cranial nerve was related to an unexpected sphenoid bone fracture and subsequent trauma in the cavernous sinus during the pterygomaxillary osteotomy.

Le Fort I osteotomy is widely used to correct various dentofacial deformities. Although safe, various complications have been reported after surgery. Serious complications are related to nerve damage. Cranial nerve damage, such as optic (CN II), oculomotor (CN III), abducens (CN VI) nerve injuries can occur after Le Fort I osteotomy. A literature review of the neurological complications related to Le Fort I osteotomy , and a recent report , showed that 7 cases of CN VI nerve palsy and 8 cases of blindness have been reported after Le Fort I osteotomy. The cranial nerve can be injured in a variety of ways but the most likely causes are unexpected pterygomaxillary separation, anatomical variation and excessive haemorrhage.

This paper reports a case of combined damage of the cranial nerves, CN II, VI, ophthalmic (CN V 1 ) and maxillary nerve (CN V 2 ), following a Le Fort I osteotomy in a patient with cleft lip and palate and investigates the possible causes.

Case report

A 19-year-old man with right complete unilateral cleft lip and palate was admitted to correct the hypoplastic maxilla and maxillofacial asymmetry with mandibular prognathism in November 2004. A cleft lip and palate repair and alveolar bone graft had been performed before he was 9 years of age. Before the orthognathic surgery, the patient was treated with pre-surgical orthodontics for dental decompensation.

The maxilla was exposed through a horseshoe shaped incision and the periosteum from the nasal floor and walls was elevated. Horizontal maxillary bone cuts were made with a saw and guided osteotomes. Pterygomaxillary disjunction for the left side was uneventful, but when separating the maxilla from the pterygoid plates on the right side, using the curved pterygoid chisel, excessive bleeding occurred. After application of packing gauze and Surgicel ® (Ethicon, NJ, USA) to the posterior maxilla, the haemorrhage was reduced and the bleeding was controlled after maxillary fixation. The maxilla was moved upward by 3 mm on the right side and downward by 2 mm on the left side and fixed with miniplates. Bilateral sagittal split ramus osteotomy for mandibular set-back (right side 10 mm, left side 3 mm) was carried out uneventfully. The anaesthesia was reversed smoothly and nasotracheal tube was maintained until the next day.

On the first postoperative day, it was noted that the patient could not move his right eye laterally ( Fig. 1 A). He complained of diplopia on right gaze and decreased vision in the right eye. Ophthalomological examination revealed decreased visual acuity, where OD (Oculus Dexter) was 0.2 and OS (Oculus Sinister) was 1.0.

Fig. 1
(A) Limited right eye ball movement 4 days after surgery. (B) Immediate postoperative CT images showing communuted fracture of right sphenoid bone and displacement of fractured fragment into cavernous sinus (arrow) and haematoma in sphenoid sinus (left). Weak contrast signal for the right internal carotid artery (right). (C) Improved right eye movement 5 months after surgery. (D) Postoperative CT at 2 months. Decreased size of bony fragment and resolution of haematoma in sphenoidal sinus (left). Postoperative MRI at 3 months shows no visible evidence of carotid-cavernous fistula. Arrow indicates partial occlusion of right internal carotid artery (right).

Slight ptosis of the right eye and paraesthesia of the right frontal and upper cheek area were also found. Pupillary constriction to light was normal on both sides. The postoperative CT scan showed three remarkable findings ( Fig. 1 B): fracture of the body of the right posterior sphenoid bone extending into the base of the skull; haematoma of the right sphenoidal sinus and cavernous sinus; a weak contrast signal for the right internal carotid artery in the cavernous sinus. Following the ophthalmological and neurological evaluation, it was concluded that the patient was showing complete paralysis of the abducens nerve (CN VI) and partial damage to the optic nerve (CN II), ophthalmic (CN V 1 ) and maxillary (CN V 2 ) branch of the trigeminal nerve related to an unexpected sphenoid bone fracture and displacement of bony fragments into the cavernous sinus. Conservative treatment and close observation was carried out because the patient had no other internal changes. Prednisolone was started and stepped down from 60 mg to 40 mg, 20 mg and 10 mg every 2 days during the course of 8 days.

Right vision improved from day 10 after the operation (OD 0.5, OS 1.0). Ptosis and partial paraesthesia of the frontal and upper buccal cheek area resolved after 2 months. Abducens nerve function started to improve from 2 months and recovery was nearly normal at 5 months ( Fig. 1 C). 2 months after surgery, a follow-up CT showed the bony fragment had decreased in size and resolution of the haematoma in the sphenoidal sinus ( Fig. 1 D, left). Follow-up MRI at 3 months showed that there was no evidence of carotid-cavernous sinus fistula formation but still showed a decreased signal for the internal carotid artery and expansion of the cavernous sinus volume ( Fig. 1 D, right). 6 months postoperatively, the vision in the right eye had recovered to nearly normal (OD 1.0, OS 1.25). The lateral rectus movement of the right eye was greatly improved, and diplopia had disappeared by the final follow-up at 12 months.

Discussion

Cranial nerve damage after Le Fort I osteotomy is rare, but reported in the literature. Isolated CN II palsy , CN III palsy and CN VI injury following maxillary osteotomy are reported. Combined cranial nerve damage, such as CN II and III , CN III and VI1 or CN II and VI has been reported.

The patient in this report could not move his right eye on the lateral side and was diagnosed with complete CN-VI palsy. As the low vision in the right eye was associated with postoperative paraesthesia on the forehead and upper cheek, partial paralysis of CN II and V 1 , V 2 was suspected. CN III nerve damage seemed to be minor and transient because the slight ptosis of the right eye resolved soon after the trauma without influencing the pupillary constriction muscle or other medial, superior or inferior rectus muscle activity.

Cranial nerve damage after the Le Fort I osteotomy is related to direct or indirect injury. Bony segments resulting from unanticipated fractures may directly injure the nerve adjacent to the fracture site. Several authors suggest that displacement of a bony fragment of the sphenoid bone is the cause of the cranial nerve damage . CN III, IV, V 1 , V 2 and VI, run through the cavernous sinus ( Fig. 2 ). CN VI crosses the cavernous sinus close to the wall of the sphenoid sinus, enters the superior orbital fissure and innervates the lateral rectus muscle. It is thus the most likely nerve to be injured if a comminuted fracture of the sphenoid bone occurs. In the cavernous sinus, CN V 1 , V 2 are located in the lateral proximity of the CN VI. Indirect injuries to the cranial nerves, such as contusion or force applied during the osteotomy might result in the ischaemia of a nutrient artery for the cranial nerves. Fracture of the skull base can cause cavernous sinus thrombosis or carotid-cavernous sinus fistula, which leads to permanent cranial nerve damage .

Feb 7, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Cranial nerve injury after Le Fort I osteotomy
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