Clinical History
A 7-month-old boy presented with orbital complaints with inability to close his left eye since birth. Birth history and family history was normal. MRI was advised and he was referred to the department of radiology.
Imaging Findings
Non-contrast MRI study was performed on 1.5T Philips machine. Routine T1-weighted and T2-weighted sequences were obtained in axial, coronal and sagittal planes. Routine sequences revealed normal brain parenchyma including posterior fossa structures. High resolution 3D CISS sequence was obtained to look for radiological anatomy of facial nerves. 3D CISS axial sequence showed absence of left facial nerve (Fig. 1). Cochlear nerve, superior and inferior vestibular nerves were normal (Fig. 2). 3D CISS sagittal sequence obtained at internal auditory canal showed three nerves with absent facial nerve which is normally seen in the anterosuperior segment.
Facial nerve on the right side was normal in calibre. Thus correlating with the clinical profile of the child, diagnosis of unilateral facial nerve aplasia was made.
Discussion
Facial nerve palsy causes are isolated non-syndromic or syndromic as seen in Moebius syndrome, Poland syndrome, Goldenhar syndrome [1], CHARGE syndrome. First isolated case of facial nerve aplasia was diagnosed as an incidental finding in a surgery which was reported by Jervis et al. [2] Facial nerve segments and canal are best visualised on MRI and CT scan, MRI with 3D CISS nerve sequence is used to detect abnormalities in cisternal and intracanalicular segment of facial nerve. 3D CISS axial, sagittal and coronal images are required for diagnosis of facial nerve abnormalities. On sagittal images intracanalicular sections show four dots of nerves with facial nerve in anterosuperior part, cochlear nerve in anteroinferior part, superior vestibular nerve in posterosuperior part and inferior vestibular nerve in posteroinferior part. Absence or thinning of dot in anterosuperior part is diagnostic of facial nerve abnormality.
Congenital facial nerve aplasia has a poor prognosis with residual function seen in few facial muscles.
Conservative treatment does not help to overcome symptoms. Surgical treatment consists of free vascularised muscle grafting. [2]
This case shows crucial importance of MRI, particularly 3D CISS sequence, in the diagnosis of congenital facial nerve palsy pertaining to anatomy, syndromic and non-syndromic causes.
It is important to differentiate syndromic and non-syndromic causes for clinical management and prognosis.
Differential Diagnosis List
Non-syndromic congenital unilateral facial nerve aplasia
Moebius syndrome
Post traumatic
Final Diagnosis
Non-syndromic congenital unilateral facial nerve aplasia
