Surgical approaches for the lateral mesencephalic sulcus

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OBJECTIVE

The brainstem is a compact, delicate structure. The surgeon must have good anatomical knowledge of the safe entry points to safely resect intrinsic lesions. Lesions located at the lateral midbrain surface are better approached through the lateral mesencephalic sulcus (LMS). The goal of this study was to compare the surgical exposure to the LMS provided by the subtemporal (ST) approach and the paramedian and extreme-lateral variants of the supracerebellar infratentorial (SCIT) approach.

METHODS

These 3 approaches were used in 10 cadaveric heads. The authors performed measurements of predetermined points by using a neuronavigation system. Areas of microsurgical exposure and angles of the approaches were determined. Statistical analysis was performed to identify significant differences in the respective exposures.

RESULTS

The surgical exposure was similar for the different approaches—369.8 ± 70.1 mm2 for the ST; 341.2 ± 71.2 mm2 for the SCIT paramedian variant; and 312.0 ± 79.3 mm2 for the SCIT extreme-lateral variant (p = 0.13). However, the vertical angular exposure was 16.3° ± 3.6° for the ST, 19.4° ± 3.4° for the SCIT paramedian variant, and 25.1° ± 3.3° for the SCIT extreme-lateral variant craniotomy (p < 0.001). The horizontal angular exposure was 45.2° ± 6.3° for the ST, 35.6° ± 2.9° for the SCIT paramedian variant, and 45.5° ± 6.6° for the SCIT extreme-lateral variant opening, presenting no difference between the ST and extreme-lateral variant (p = 0.92), but both were superior to the paramedian variant (p < 0.001). Data are expressed as the mean ± SD.

CONCLUSIONS

The extreme-lateral SCIT approach had the smaller area of surgical exposure; however, these differences were not statistically significant. The extreme-lateral SCIT approach presented a wider vertical and horizontal angle to the LMS compared to the other craniotomies. Also, it provides a 90° trajectory to the sulcus that facilitates the intraoperative microsurgical technique.

ABBREVIATIONS LMS = lateral mesencephalic sulcus; PCA = posterior cerebral artery; SCA = superior cerebellar artery; SCIT = supracerebellar infratentorial; ST = subtemporal.

Article Information

Correspondence Eberval Gadelha Figueiredo: University of São Paulo School of Medicine, São Paulo, Brazil. ebgadelha@yahoo.com.

INCLUDE WHEN CITING Published online April 12, 2019; DOI: 10.3171/2019.1.JNS182036.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

Headings

Figures

  • View in gallery

    ST approach. A: Cadaveric head laterally positioned with the sagittal suture parallel to the floor and with contralateral lateral flexion. A vertical incision is placed in front of the tragus. B: Dural exposure after left temporal craniotomy. C: Dura opened in a U-shaped fashion and inferiorly retracted, exposing the temporal lobe. D: Lateral view of the anterior tentorial hiatus and an oblique view of the lateral mesencephalic zone. At the right side we can identify the internal carotid artery (ICA) and posterior communicating artery (PCoA); at the center the PCA’s P1 and P2A segments and the oculomotor nerve (CN III); caudally the medial posterior choroidal artery is seen. E: The area of exposure provided by this approach includes the lateral midbrain surface, LMS, and oblique views of the lateral mesencephalic zone. The PCA segments P2A and P2P are visualized. F: The surgical exposure becomes significantly larger after the tentorial edge opening, providing exposure of the pontomesencephalic junction, ipsilateral trochlear nerve (CN IV), and SCA. The LMS is represented with a green dashed line. Figure is available in color online only.

  • View in gallery

    Paramedian SCIT approach. A: Semisitting position. A vertical linear incision equally distant from the retrosigmoid and median incision. B: Exposure of miofascial layer and occipital artery. C: A burr hole is drilled just cranial to the transverse sinus. D: Rectangular suboccipital craniotomy. E: Dura opened in a U-shaped fashion and superiorly retracted to fully expose the transverse sinus and widen the visual field of the supracerebellar cistern. F: Surgical exposure with an oblique view of the cerebellomesencephalic fissure, and the quadrigeminal and ambient cisterns. V. = vein. Figure is available in color online only.

  • View in gallery

    Extreme-lateral SCIT approach. A: Semisitting position. A retroauricular straight skin incision is represented. B: A modified retrosigmoid craniotomy is tailored to extend just above the transverse sinus. C: Dissection is carried out at the superior surface of the cerebellum. D: Exposure of a few bridging veins. These veins can be coagulated near the cortex surface. E: After dissecting the arachnoid, exposure of the cerebellomesencephalic fissure and oblique view of the quadrigeminal cistern. F: The trochlear nerve (CN IV) is seen crossing the cistern, along the SCA and distal branches of the PCA. Perpendicular view to the LMS. Transv. = transverse. Figure is available in color online only.

  • View in gallery

    Posterolateral view of the brainstem. The gray shaded area corresponds to the area exposure of the extreme-lateral SCIT approach, the pink shaded area corresponds to the paramedian SCIT approach, and the blue shaded area to the ST approach. The LMS is represented with a green dashed line. Figure is available in color online only.

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