Topographic Anatomy of the Medial Labyrinthine Wall: Implications for the Transcanal Endoscopic Approach to the Internal Auditory Canal.

Hypothesis To characterize transcanal endoscopic landmarks of the medial labyrinthine wall and correlate these with anatomical features of the fundus of the internal auditory canal (IAC). Background The transcanal transpromontorial approach (TTA) enables minimally invasive access to the IAC. The establishment of a landmark-based dissection technique for the approach is crucial to avoid injury to the facial nerve. Methods Twenty temporal bones were dissected endoscopically through the TTA. Furthermore, high-resolution computed tomography (CT) scans from ten adult normal temporal bones were analyzed and three-dimensionally reconstructed. Results A stepwise dissection technique for the TTA was demonstrated depending on a newly described landmark used in the identification of the facial nerve. The proposed landmark, which was named the intervestibulocochlear crest (IVCC), is an integrated part of the otic capsule. It can be differentiated after the excision of the lateral labyrinthine wall as a laterally based bony pyramid between the cochlea and the vestibule. Its medially directed apex blends with the central part of the falcifrom crest and points to the distal part of the meatal facial nerve. The IVCC is best detected on axial CT images at the level of the tympanic facial nerve. The union between the IVCC and the falciform crest appears radiologically as a short stem or mini-martini glass. Conclusion The proposed IVCC is a novel landmark with a consistent relationship to the IAC fundus and the facial nerve. It may be utilized in conjunction with the falciform crest to identify the facial nerve during minimally invasive transcanal surgeries. METHODS Twenty temporal bones were dissected endoscopically through the TTA. Furthermore, high-resolution computed tomography (CT) scans from ten adult normal temporal bones were analyzed and three-dimensionally reconstructed. RESULTS A stepwise dissection technique for the TTA was demonstrated depending on a newly described landmark used in the identification of the facial nerve. The proposed landmark, which was named the intervestibulocochlear crest (IVCC), is an integrated part of the otic capsule. It can be differentiated after the excision of the lateral labyrinthine wall as a laterally based bony pyramid between the cochlea and the vestibule. Its medially directed apex blends with the central part of the falcifrom crest and points to the distal part of the meatal facial nerve. The IVCC is best detected on axial CT images at the level of the tympanic facial nerve. The union between the IVCC and the falciform crest appears radiologically as a short stem or mini-martini glass. CONCLUSION The proposed IVCC is a novel landmark with a consistent relationship to the IAC fundus and the facial nerve. It may be utilized in conjunction with the falciform crest to identify the facial nerve during minimally invasive transcanal surgeries

Anatomic Variations of the Sphenoid Sinus and Their Impact on Trans-sphenoid Pituitary Surgery

Introduction: The trans-sphenoid access to the pituitary gland is becoming the most common approach for pituitary adenomas. Preoperative evaluation of the anatomy of the sphenoid sinus by computed tomography (CT) scan and magnetic resonance imaging (MRI) is a routine procedure and can direct the surgical decision. Purpose: This work determines the incidence of the different anatomical variations of the sphenoid sinus as detected by MRI and CT scan and their impact on the approach. Methods: The CT scan and MRI of 296 patients operated for pituitary adenomas via a trans-sphenoid approach were retrospectively reviewed regarding the different anatomical variations of the sphenoid sinus: degree of pneumatization, sellar configuration, septation pattern, and the intercarotid distance. Results: There were 6 cases with conchal pneumatization, 62 patients with presellar, 162 patients with sellar, and 66 patients with postsellar pneumatization. There was sellar bulge in 232 patients, whereas this bulge was absent in 64 patients. There was no intersphenoid sinus septum in 32 patients, a single intersphenoid septum in 212 patients, and an accessory septum in 32 patients. Intraoperatively, the sellar bulge was marked in 189 cases and was mild in 43 cases. Discussion: The pattern of pneumatization of the sphenoid sinus significantly affects the safe access to the sella. A highly pneumatized sphenoid sinus may distort the anatomic configuration, so in these cases it is extremely important to be aware of the midline when opening the sella to avoid accidental injury to the carotid and optic nerves. The sellar bulge is considered one of the most important surgical landmarks, facilitating the access to the sella. The surgical position of the patient is also a crucial point to avoid superior or posterior misdirection with resultant complications. It is wise to use extreme caution while removing the terminal septum. Conclusion: Different anatomical configurations of the sphenoid sinus can seriously affect the access to the sella via the nose. The surgeon should be aware of these findings preoperatively to reach the sella safely and effectively

Magnesium sulphate optimises surgical field without attenuation of the stapaedius reflex in paediatric cochlear implant surgery

Background and Aims: The anaesthesia technique for paediatric cochlear implantation should be modified to achieve an optimised surgical field and allow neuromonitoring. Total intravenous anaesthesia (TIVA) provides good surgical condition without affecting intraoperative electrical stapaedial reflex threshold (ESRT). Though magnesium sulphate (MgSO4) is a cheap, readily available drug for controlled hypotension, it can decrease the amplitude of motor-evoked potentials. This study aimed to evaluate the effect of MgSO4 infusion on quality of surgical field, intraoperative ESRT, and anaesthetic requirements in paediatric cochlear implant surgery performed under TIVA. Methods: In this randomised controlled trial, 66 children (1-6 years) undergoing cochlear implant under TIVA were randomly assigned to control group or MgSO4 group. The primary outcome was quality of surgical field, and the secondary outcomes were mean arterial blood pressure (MAP), heart rate (HR), ESRT, and the intraoperative anaesthetic requirements. The incidence of adverse events was recorded as well. Results: The quality of surgical field was better in group M than group C, P < 0.02. The number of children who achieved optimum surgical conditions (scores ≤2) was significantly better in the group M (n = 23/33, 70%) compared with group C (n = 13/33, 39%), P < 0.001. MAP, HR, and anaesthetic requirements were significantly lower in group M, P < 0.05. There were no differences between both groups regarding ESRT response. Conclusion: Magnesium sulphate IV infusion optimised surgical field and decreased anaesthetic requirements without attenuating the ESRT in paediatric cochlear implant surgery performed under TIVA