The Usefulness of Reconstructed 3D Images in Surgical Planning for Cochlear Implantation in a Malformed Ear with an Abnormal Course of the Facial Nerve

Surgical considerations during cochlear implantation: the utility of temporal bone computed tomography

OBJECTIVE

This paper describes the construction of portals for electrode placement during cochlear implantation and emphasises the utility of pre-operative temporal bone three-dimensional computed tomography.

METHODS

Temporal bone three-dimensional computed tomography was used to plan portal creation for electrode insertion.

RESULTS

Pre-operative temporal bone three-dimensional computed tomography can be used to determine the orientation of temporal bone structures, which is important for mastoidectomy, posterior tympanotomy and cochleostomy, and when using the round window approach.

CONCLUSION

It is essential to create appropriate portals (from the mastoid cortex to the cochlea) in a step-by-step manner, to ensure the safe insertion of electrodes into the scala tympani. Pre-operative three-dimensional temporal bone computed tomography is invaluable in this respect.

Human Inner-ear Malformation Types Captured in 3D

OBJECTIVES

Capture the human inner-ear malformation types in 3D by segmenting the inner-ear structures from clinical CT (computed tomography) and MR (magnetic resonance) image datasets. Volumetric analysis was done to find the variations in the volume of cochlear part alone from complete inner-ear followed by 3D printing from the 3D segmented models.

MATERIALS AND METHODS

Using 3D slicer freeware, the complete inner-ear structures were segmented from anonymized CT and MR image by setting a tight grey-scale threshold to avoid capturing unwanted structures followed by volumetric analysis of the cochlear part alone. 3D printing was done using Form labs desktop 3D printer.

RESULTS

We identified 2x normal anatomy (NA) cochlea, 1x enlarged vestibular aqueduct syndrome (EVAS), 3x incomplete partition (IP) type-I, 4x IP type-II, 3x IP type-III, 5x common cavity (CC) and 5x cochlear hypoplasia (CH). 3D segmented models along with the 3D printed models showed huge variation in size, shape and the anatomy among the image data-sets analyzed. Volumetric analysis showed that on average, volume of CC was above 150mm3, volume of CH fell below 80mm3, Volume of NA, EVAS and IP-I were all around 85-105mm3 whereas the volume of IP-II was around 50mm3.

CONCLUSION

Visualizing human inner-ear malformation types in 3D both as computer models and as 3D printed models is a whole-new experience as demonstrated in this study. The volumetric analysis showed a huge variation among the volume of cochlear part alone among the malformation types.

Variations in the Size and Shape of Human Cochlear Malformation Types

The objective of this study is to determine the variations in size and shape of the most widely recognized cochlear malformation types using three-dimensional (3D) visualization. Using 3D slicer freeware, the complete inner-ear structures were segmented from 46 anonymized high-resolution computed tomography (HRCT) image datasets. Cochlear height, internal auditory canal height, and width were measured from the axial plane. Cochlear basal turn diameter was measured from the oblique coronal plane. Number of cochlear turns was measured from the 3D images and the corresponding cochlear duct length (CDL) was estimated using the CDL equations given in Alexiades et al. [Otol Neurotol 36 (2015) 904-907]. Out of 46 preoperative HRCT image datasets of human temporal bone, cochlear anatomy types including normal anatomy (4), enlarged vestibular aqueduct syndrome (3), cochlear aplasia (2), incomplete partition Types I (8), II (Mondini's deformity) (3), and III (X-linked) (4), cochlear hypoplasia (CH) (17), and common cavity (CC) (5) were identified. Majority of CH cases had cochlear height shorter than 4 mm whereas the CC cases measured cochlear height above 6 mm. For all the other malformation types, cochlear height was between 4 and 6 mm. In terms of "A" value, majority of CH cases showed shorter "A" value of <7.5 mm, which is in the lower end in comparison to the rest of the malformation types reported in this study. 3D-visualization shows the size and shape variations of all the structures of inner ear and also improves the clinicians' ability to visualize cochlear anatomy and nearby structures much easier than from the 2D image slices. Anat Rec, 302:1792-1799, 2019. © 2019 The Author. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association for Anatomy.

[The modern state and prospects of development of endoscopic otosurgery]

In this review presents data on efficiency endoscopic operations at some ear diseases. Now endoscopic operations are widely applied at primary and residual (or recuring) middle ear cholesteatomas, tympanic membrane perforation, otosclerosis and cochlear implantation. Proceeding from resolving power of endoscopic technology, endoscopic operation can be applied as an independent method, or as an endoscopic assisted, to be combined with otomicrosurgery operation. Efficiency of endoscopic operation in many respects is defined by a possibility of panoramic visualization of anatomical structures of middle and inner ear, and also carrying out high-quality elimination of focus lesion from areas, being remote when performing otomicrosurgery operation.

The feasibility of endoscopic transcanal approach for insertion of various cochlear electrodes: a pilot study

To determine the feasibility of inserting various types of electrode arrays using an endoscopic transcanal approach into the cochlea via the round window membrane (RWM). All the procedures were performed by the first author and started with a cortical mastoidectomy. A six o'clock vertical incision was made in the meatal skin, and a posterior tympano-meatal flap was elevated transmeatally to expose the middle ear cavity using a rigid 0° endoscope (diameter 3 mm, length 14 cm). The chorda tympani nerve (CTN) and body of the incus were exposed. The RWM was incised, and the electrodes were passed through the tunnel from the mastoid to the epitympanum, medial to the CTN and lateral to the incus into the round window (RW) in seven procedures. In the other six cases, an open groove had been drilled, starting superiorly and laterally to the CTN and ending in the mastoid region. After electrodes insertion, the groove was filled with bone dust and covered with a large piece of fascia prior to repositioning of the tympano-meatal flap. Complete electrode insertion (7 Nucleus Contour Advance, 5 Concerto and 1 HiRes90K) via the RW was achieved in all 13 cases. Endoscopic CI was more feasible for insertion of concerto electrode followed by HiRes90K and Nucleus. An assistance of another surgeon was required for removal of stylet in the "off-the-stylet technique" utilized for implantation of nucleus electrode. Endoscopic transcanal implantation of different cochlear electrodes through the RW is feasible in both children and adults and can be used as first surgical option or as a complementary to the traditional posterior tympanotomy approach.

Surgery of the ear and the lateral skull base: pitfalls and complications

Surgery of the ear and the lateral skull base is a fascinating, yet challenging field in otorhinolaryngology. A thorough knowledge of the associated complications and pitfalls is indispensable for the surgeon, not only to provide the best possible care to his patients, but also to further improve his surgical skills. Following a summary about general aspects in pre-, intra-and postoperative care of patients with disorders of the ear/lateral skull base, this article covers the most common pitfalls and complications in stapes surgery, cochlear implantation and surgery of vestibular schwannomas and jugulotympanal paragangliomas. Based on these exemplary procedures, basic "dos and don'ts" of skull base surgery are explained, which the reader can easily transfer to other disorders. Special emphasis is laid on functional aspects, such as hearing, balance and facial nerve function. Furthermore, the topics of infection, bleeding, skull base defects, quality of life and indication for revision surgery are discussed. An open communication about complications and pitfalls in ear/lateral skull base surgery among surgeons is a prerequisite for the further advancement of this fascinating field in ENT surgery. This article is meant to be a contribution to this process.

Using coronary computerized tomographic images to predict the bulging second genu of the facial nerve in mastoidectomy

The aim of the present study is to determine whether coronary CT images of the temporal bone are useful to predict a bulging second genu of the facial nerve (SGFN) in mastoidectomy by measuring and comparing the heights of the SGFN above the prominence of the lateral semicircular canal (PLSC) in medial-to-lateral dimension on coronary CT images and in mastoidectomy. The relationship between the SGFN and the PLSC in medial-to-lateral dimension, which may have big variability, can be evaluated on the coronary CT images of the temporal bone. The heights of the SGFN above the PLSC in medial-to-lateral dimension were measured on coronary CT images and in mastoidectomy in 184 patients. If the SGFN is above the PLSC in medial-to-lateral dimension, we called the SGFN a bulging SGFN. The data measured on CT images and in surgery were described in histograms and compared. The sensitivity and the specificity in the diagnosis of a bulging SGFN on CT images were calculated by comparison with surgical measurement. Cohen's kappa coefficient was calculated. The heights of the SGFN above the PLSC measured in medial-to-lateral dimension varied from -2.9 to 2.9 mm on coronary CT images and varied from -3.0 to 3.0 mm in surgery. The data measured in surgery showed that the SGFN was above the PLSC in medial-to-lateral dimension in 27.7% (51/184) patients, at least 1 mm above the PLSC in 15.8% (29/184) patients and at least 2 mm above the PLSC in 6.0% (13/184) patients. The sensitivity and the specificity for CT diagnosis of a bulging SGFN were 100% (51/51) and 91.0% (121/133), respectively. Bulging SGFN can be predicted by measuring the height of the SGFN above the PLSC on coronary CT images of the temporal bone.

Surgical and radiologic anatomy of a cochleostomy produced via posterior tympanotomy for cochlear implantation based on three-dimensional reconstructed temporal bone CT images

PURPOSE

In this study, we evaluated the surgical and radiologic anatomy of a cochleostomy produced via posterior tympanotomy for cochlear implantation (CI).

MATERIALS AND METHODS

Twenty computed tomography (CT) images of the temporal bone from patients aged between 20 and 60 years were selected. The inclusion criterion was a radiologically normal temporal bone CT scan. Three-dimensional (3D) reconstructed images were obtained using high-resolution axial temporal bone CT scans. Eight points were used to evaluate the surgical anatomy of the posterior tympanotomy and cochleostomy. The length of lines between the points and the angles between the lines were measured.

RESULTS

The mean length of line AB (superior-inferior length of the posterior tympanotomy for CI) was 6.48 ± 0.26 mm, while line AC (width of the chorda tympani and facial nerves) was 3.60 ± 0.2 mm. The mean angle of ABC (angle at which the chorda tympani nerve branched from the facial nerve) was 18.40° ± 1.05°. The mean length of line AD (distance from the facial ridge to the point of cochleostomy) was 9.58 ± 0.47 mm.

CONCLUSIONS

3D imaging of the facial recess and round window can be used to identify the facial recess before surgery. This may help to avoid injury to the chorda tympani nerve during posterior tympanotomy, and make it easier to insert the electrode array during CI by creating a large enough posterior tympanotomy to avoid injury to the facial nerve, which can cause immediate or delayed facial palsy.