Radiological requirements for surgical planning in cochlear implant candidates

Mohamad Hasan Alam-Eldeen, Usama Mohamed Rashad, Al Hussein Awad Ali, Mohamad Hasan Alam-Eldeen, Usama Mohamed Rashad, Al Hussein Awad Ali

Abstract

Objective: This study is concerned with clarification of radiological findings that should be addressed and reported in patients listed for cochlear implant (CI) operation. These findings may force a surgeon to consider modifications of the surgical approach by a CI surgeon.

Materials and methods: The study was performed from January 2015 to January 2016. It included 50 patients with severe-to-profound sensorineural hearing loss who fulfilled the criteria for CI. Patients underwent CI surgery in the Department of Otolaryngology. All patients underwent preoperative computed tomography (CT) and magnetic resonance imaging (MRI) assessment in the Department of Diagnostic Radiology. Combined examination of the CT and MRI by the radiologist and the surgeon was advocated.

Results: Many anatomical variants were observed regarding the pattern of mastoid pneumatization, position of middle cranial fossa dura, sigmoid sinus position jugular bulb position, and the size and position of the mastoid segment of facial nerve canal. Labyrinthitis ossificans was seen in 3 patients (6%), otospongiosis in 1 patient (2%), and dilated vestibular aqueduct and endolymphatic sac in 9 patients (18%).

Conclusion: Cochlear implantation is a major treatment modality in patients with severe-to-profound sensorineural hearing loss. Radiological evaluation is integral in surgery planning.

Keywords: Cochlear implantation; computed tomography; magnetic resonance imaging; surgical considerations.

Conflict of interest statement

There are no conflicts of interest.

Figures

Figure 1 (A-F)
Figure 1 (A-F)
Different patterns of mastoid pneumatization. (A) Normal pneumatization. (B) Hyperpneumatization. (C) Hypoplastic diploic mastoid, note deep anterior position of sigmoid sinus. (D) Diploic mastoid. (E) Partially pneumatic (white arrow) partially diploic (black arrow) mastoid. (F) Mixed, pneumatic (white arrow), diploic (black arrow) and sclerotic (dashed black arrow) mastoid
Figure 2 (A and B)
Figure 2 (A and B)
Dura position. (A) Normal dura position lying at the same level of attic roof. (B) Low lying dura which is at a lower level than attic roof
Figure 3
Figure 3
Korner's septum
Figure 4 (A-H)
Figure 4 (A-H)
Sequential axial CT images showing the course of mastoid emissary vein
Figure 5 (A-C)
Figure 5 (A-C)
Sigmoid sinus variations. (A) Normal position of sigmoid sinus. (B) Lateral position of sigmoid sinus. (C) Anterolateral position of sigmoid sinus. Note diploic hypoplastic mastoid in (B) and (C)
Figure 6 (A-F)
Figure 6 (A-F)
Jugular bulb variations. (A) Normal jugular bulb; (B) high riding bulb; (C) giant bulb; (D) high riding giant bulb; (E and F) axial and coronal scans of dehiscent jugular bulb
Figure 7 (A-F)
Figure 7 (A-F)
Sequential axial images from superior to inferior showing normal position of the mastoid segment of facial N. and facial recess which lie posterior to the round window niche suggesting adequate visualization and open accessibility of the round window during surgery. Facial N. (short arrow), chorda tympani nerve (dashed arrow), round window niche (long arrow)
Figure 8 (A-F)
Figure 8 (A-F)
Sequential axial images from superior to inferior showing abnormal anterior position of the mastoid segment of facial N. and facial recess in relation to the round window niche which is expected to hinder the visualization of the round window with difficult accessibility during surgery. Facial N. (short arrow), chorda tympani nerve (dashed arrow), round window niche (long arrow)
Figure 9 (A and B)
Figure 9 (A and B)
Axis of the basal turn of cochlea (dashed arrow) in relation to axis of ICA canal (solid arrow). (A) The axis of cochlea basal turn is parallel to that of ICA canal with expected open accessibility of round window during surgery. (B) Posterior rotation of axis of cochlea basal turn in relation to that of ICA canal with expected difficult accessibility of round window during surgery
Figure 10 (A-F)
Figure 10 (A-F)
Normal cochlea and labyrinthitis ossificans. Normal cochlea on (A) axial CT, (B) oblique coronal MPR CT, (C) axial MRI. Labyrinthitis ossificans on (D-F)
Figure 11 (A-D)
Figure 11 (A-D)
Normal cochlea and otospongiosis. Normal cochlea on (A) axial CT, (B) oblique coronal MPR CT. Otospongiosis on (C and D)
Figure 12 (A-D)
Figure 12 (A-D)
Normal and dilated vestibular aqueduct. (A and B) CT shows (A) normal vestibular aqueduct, (B) dilated vestibular aqueduct. (C and D) MRI shows (C) normal vestibular aqueduct, (D) dilated vestibular aqueduct and endolymphatic sac
Figure 13 (A and B)
Figure 13 (A and B)
Normal cochlear nerve on MRI. (A) Axial MRI on left IAC showing the plane at which sagittal oblique images were obtained. (B) sagittal oblique at mid IAC showing the cochlear nerve anteroinferiorly (short white arrow), facial nerve anterosuperiorly (dashed white arrow), superior and inferior vestibular nerves posteriorly (long white arrows)

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