Euclidean Relationship between the Superior Semicircular Canal and the Arcuate Eminence

Surgical morbidity of the extradural anterior petrosal approach: the Lariboisière experience

OBJECTIVE

Concerns about the approach-related morbidity of the extradural anterior petrosal approach (EAPA) have been raised, especially regarding temporal lobe and venous injuries, hearing impairment, facial nerve palsy, cerebrospinal fluid fistula, and seizures. There is lack in the literature of studies with detailed analysis of surgical complications. The authors have presented a large series of patients who were treated with EAPA, focusing on complications and their avoidance.

METHODS

The authors carried out a retrospective review of patients who underwent EAPA at their institution between 2012 and 2021. They collected preoperative clinical characteristics, operative reports, operative videos, findings on neuroimaging, histological diagnosis, postoperative course, and clinical status at last follow-up. For pathologies without petrous bone invasion, the amount of petrous apex drilling was calculated and classified as low (< 70% of the volume) or high (≥ 70%). Complications were dichotomized as approach related and resection related.

RESULTS

This study included 49 patients: 26 with meningiomas, 10 brainstem cavernomas, 4 chondrosarcomas, 4 chordomas, 2 schwannomas, 1 epidermoid cyst, 1 cholesterol granuloma, and 1 osteoblastoma. The most common approach-related complications were temporal lobe injury (6.1% of patients), seizures (6.1%), pseudomeningocele (6.1%), hearing impairment (4.1%), and dry eye (4.1%). Approach-related complications occurred most commonly in patients with a meningioma (p = 0.02) and Meckel's cave invasion (p = 0.02). Gross-total or near-total resection was correlated with a higher rate of tumor resection-related complications (p = 0.02) but not approach-related complications (p = 0.76). Inferior, lateral, and superior tumoral extension were not correlated with a higher rate of tumor resection-related complications. No correlation was found between high amount of petrous bone drilling and approach- or resection-related complications.

CONCLUSIONS

EAPA is a challenging approach that deals with critical neurovascular structures and demands specific skills to be safely performed. Contrary to general belief, its approach-related morbidity seems to be acceptable at dedicated skull base centers. Morbidity can be lowered with careful examination of the preoperative neuroradiological workup, appropriate patient selection, and attention to technical details.

Anatomical study between the correlation of the arcuate eminence and the superior semicircular canal

OBJECTIVE

To study the anatomical correlation between the arcuate eminence and the superior semicircular canal.

MATERIAL AND METHODS

A study of the height of the arcuate eminence was carried out in 295 temporal bones. In addition, 30 temporals with different heights of the arcuate eminence (10 flat, 10 prominent and 10 very prominent) were randomly selected and radiological tests were performed by computed tomography (Pöschl projection) and subsequent dissection by milling until the apex of the superior semicircular canal was found, establishing, with both methods, the anatomical relationship with the arcuate eminence.

RESULTS

The arcuate eminence was classified as: smooth, when there was no relief (1.7%); flat, measured less than 1 mm (20.3%), prominent, measured between 1 and 2 mm, in (62%), and very prominent, measured above 2 mm (12.6%). The tomographic study (CT) and its subsequent dissection by bone milling showed a direct relationship between the arcuate eminence and the semicircular canal only when it was flat, while the rest of the types corresponded to the presence of pneumatized peri-labyrinthine cells and/or cancellous bone without a direct anatomical relationship with the apex of the superior semicircular canal.

CONCLUSION

The correlation between the arcuate eminence and the superior semicircular canal is direct only when it is flat (1 mm), being related to peri-labyrinthine cells and/or cancellous bone when the arcuate eminence is prominent or very prominent.

Is the Height of the Arcuate Eminence Related to Body Mass Index?

OBJECTIVES

To determine the relationship, if any, between body mass index (BMI) and attenuation of the arcuate eminence (AE).

STUDY DESIGN

Case series with chart review.

SETTING

Tertiary neurotologic referral center.

SUBJECTS AND METHODS

Submillimeter distances were recorded from high-resolution temporal bone computed tomography (CT) scans of 50 patients (100 sides). The AE (defined as the superiormost location of the petrous bone over the otic capsule), the bony apex of the superior semicircular canal (SSC), and the geniculate ganglion (GG) were identified and 3-dimensional distances measured. The height of the AE relative to the bony apex of the superior semicircular canal was determined using Euclidean geometry using the fixed anatomical landmark of the GG as the origin. Correlations between AE and BMI were calculated using Pearson's, linear mixed effects, and sensitivity analysis models.

RESULTS

The mean (SD) BMI was 30 (8.1) kg/m², with 16 (30%) patients falling in the underweight/normal category (BMI <25 kg/m²), 10 (20%) overweight patients (25 kg/m²≤ BMI ≤ 30 kg/m²), and 24 (48%) patients considered obese (BMI >30 kg/m²). The mean (SD) AE heights for the left and right ears were 2.5 (1.11) and 2.6 (1.09), respectively. The results of the linear mixed-effects models indicated little evidence that BMI is associated with AE height when including all patients (partial R² = 0.040) and when using BMI categories (partial R² = 0.025).

CONCLUSION

Contrary to other structures within the lateral skull base, the relative prominence of the arcuate eminence does not correlate with BMI or any other demographic variables.