Patulous Internal Auditory Canals: A Normal Variant
Correspondence Address :
Upasana Ranga, MD
Assistant professor
Department of Radiodiagnosis and Imaging
Saveetha Medical College and Hospital, Thandalam
Kanchipuram, Tamilnadu – 602105, India.
Phone: 91-44-26811173 (O), 91-9176549556 (Mob)
Fax: 91-44-26811999
E-mail: upasranga@yahoo.co.in
We report here, a case of bilateral, dilated, internal auditory canals, a normal anatomical variant which clinically and radiologically has to be differentiated from other pathological causes of dilated internal auditory canals.
Internal auditory canals, Patulous, Variant
Introduction
A 40-year-old male came with complaints of headache. The computed tomography (CT) scan of the brain showed no significant intra-cranial abnormality, except for bilateral, dilated, internal auditory canals (IAC). Dedicated sections of the temporal bone revealed the same findings (Table/Fig 1). The inner ear structures were normal, with intact crista falciformis. The cortical outlines of both the IACs were smooth, with no bony erosions. Examination by an otolaryngologist showed no abnormality. Magnetic resonance imaging (MRI) was advised to rule out the underlying pathology. MRI showed dilatation of the bilateral IACs, especially in their mid portions (Table/Fig 2). No obvious mass lesion was noted within the IAC or in the cerebellopontine angles. Bilateral seventh and eight cranial nerves were normal. MRI screening of the brain and spine showed no abnormality.
Patulous IAC is an anatomic variant of the auditory canals, which is characterized by dilated IACs (especially in the mid portion),with normal inner ear structures (1). Though it is mostly bilateral, unilateral involvement has also been described. This condition has to be differentiated from the pathological causes of dilated IAC, the commonest being acoustic neuroma, which is seen in neurofibromatosis II, in association with cortical erosion. The dilatation of the IACs may be caused by increased local pressure, which is seen in patients with chronic hydrocephalus and dural ectasia (in neurofibromatosis) (2). Dilated IACs can also be seen in syndromes such as Goldenhar syndrome, Apert syndrome and Patau syndrome in association with a defective fundus and crista falciformis (3). The presence of a smooth cortical outline and a normal fundus with intact crista falciformis is therefore necessary to differentiate the normal variant from the pathological causes of dilated IACs (4).
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