Surgical treatment of ventral mesencephalic cavernoma

Endoscopic Endonasal Transclival Approach to the Ventral Brainstem: Anatomic Study of the Safe Entry Zones Combining Fiber Dissection Technique with 7 Tesla Magnetic Resonance Guided Neuronavigation

BACKGROUND

Treatment of intrinsic lesions of the ventral brainstem is a surgical challenge that requires complex skull base antero- and posterolateral approaches. More recently, endoscopic endonasal transclival approach (EETA) has been reported in the treatment of selected ventral brainstem lesions.

OBJECTIVE

In this study we explored the endoscopic ventral brainstem anatomy with the aim to describe the degree of exposure of the ventral safe entry zones. In addition, we used a newly developed method combining traditional white matter dissection with high-resolution 7T magnetic resonance imaging (MRI) of the same specimen coregistered using a neuronavigation system.

METHODS

Eight fresh-frozen latex-injected cadaver heads underwent EETA. Additional 8 formalin-fixed brainstems were dissected using Klingler technique guided by ultra-high resolution MRI.

RESULTS

The EETA allows a wide exposure of different safe entry zones located on the ventral brainstem: the exposure of perioculomotor zone requires pituitary transposition and can be hindered by superior cerebellar artery. The peritrigeminal zone was barely visible and its exposure required an extradural anterior petrosectomy. The anterolateral sulcus of the medulla was visible in most of specimens, although its close relationship with the corticospinal tract makes it suboptimal as an entry point for intrinsic lesions. In all cases, the use of 7T-MRI allowed the identification of tiny fiber bundles, improving the quality of the dissection.

CONCLUSION

Exposure of the ventral brainstem with EETA requires mastering surgical maneuvers, including pituitary transposition and extradural petrosectomy. The correlation of fiber dissection with 7T-MRI neuronavigation significantly improves the understanding of the brainstem anatomy.

The oculomotor-tentorial triangle. Part 1: microsurgical anatomy and techniques to enhance exposure

OBJECTIVE

Access to the ventrolateral pontomesencephalic area may be required for resecting cavernous malformations, performing revascularization of the upper posterior circulation, and treating vascular lesions such as aneurysms. However, such access is challenging because of nearby eloquent structures. Commonly used corridors to this surgical area include the optico-carotid, supracarotid, and carotid-oculomotor triangles. However, the window lateral to the oculomotor nerve can also be used and has not been studied. The authors describe the anatomical window formed between the oculomotor nerve and the medial tentorial edge (the oculomotor-tentorial triangle [OTT]) to the ventrolateral pontomesencephalic area, and assess techniques to expand it.

METHODS

Four cadaveric heads (8 sides) underwent orbitozygomatic craniotomy. The OTT was exposed via a pretemporal approach. The contents of the OTT were determined and their anatomical features were recorded. Also, dimensions of the brainstem surface exposed lateral and inferior to the oculomotor nerve were measured. Measurements were repeated after completing a transcavernous approach (TcA), and after resection of temporal lobe uncus (UnR).

RESULTS

The s1 segment and proximal s2 segment of the superior cerebellar artery (SCA) and P2A segment of the posterior cerebral artery (PCA) were the main contents of the OTT, with average exposed lengths of 6.4 ± 1.3 mm and 5.5 ± 1.6 mm for the SCA and PCA, respectively. The exposed length of the SCA increased to 9.6 ± 2.7 mm after TcA (p = 0.002), and reached 11.6 ± 2.4 mm following UnR (p = 0.004). The exposed PCA length increased to 6.2 ± 1.6 mm after TcA (p = 0.04), and reached 10.4 ± 1.8 mm following UnR (p < 0.001). The brainstem surface was exposed 7.1 ± 0.5 mm inferior and 5.6 ± 0.9 mm lateral to the oculomotor nerve initially. The exposure inferior to the oculomotor nerve increased to 9.3 ± 1.7 mm after TcA (p = 0.003), and to 9.9 ± 2.5 mm after UnR (p = 0.21). The exposure lateral to the oculomotor nerve increased to 8.0 ± 1.7 mm after TcA (p = 0.001), and to 10.4 ± 2.4 mm after UnR (p = 0.002).

CONCLUSIONS

The OTT is an anatomical window that provides generous access to the upper ventrolateral pontomesencephalic area, s1- and s2-SCA, and P2A-PCA. This window may be efficiently used to address various pathologies in the region and is considerably expandable by TcA and/or UnR.

Microroll retractor for surgical resection of brainstem cavernomas

BACKGROUND

Safe and complete surgical resection of brainstem cavernoma is difficult without injury surrounding normal structures because the lesions are deep and intra-axial. In this article, the authors describe the "microroll retractor" technique for brainstem cavernoma surgery.

METHODS

The microroll retractor is made of expanded polytetrafluoroethylene sheet. The sheet is cut in several sizes of square piece and transformed into a tubular shape. We insert this roll retractor via minimal brain incision and keep surgical corridor without usual spatulas during lesionectomy.

RESULTS

This technique was adopted for 7 patients with brainstem cavernomas. In all patients, we achieved total excision; improvement was recorded in 6 patients, and no change was recorded in 1 patient.

CONCLUSIONS

The microroll retractor is extremely simple but provides enough surgical corridors for safe total resection of brainstem cavernomas.

Supratentorial cavernous malformations in eloquent and deep locations: surgical approaches and outcomes. Clinical article

OBJECT

Resection of cavernous malformations (CMs) located in functionally eloquent areas of the supratentorial compartment is controversial. Hemorrhage from untreated lesions can result in devastating neurological injury, but surgery has potentially serious risks. We hypothesized that an organized system of approaches can guide operative planning and lead to acceptable neurological outcomes in surgical patients.

METHODS

The authors reviewed the presentation, surgery, and outcomes of 79 consecutive patients who underwent microresection of supratentorial CMs in eloquent and deep brain regions (basal ganglia [in 27 patients], sensorimotor cortex [in 23], language cortex [in 3], thalamus [in 6], visual cortex [in 10], and corpus callosum [in 10]). A total of 13 different microsurgical approaches were organized into 4 groups: superficial, lateral transsylvian, medial interhemispheric, and posterior approaches.

RESULTS

The majority of patients (93.7%) were symptomatic. Hemorrhage with resulting focal neurological deficit was the most common presentation in 53 patients (67%). Complete resection, as determined by postoperative MR imaging, was achieved in 76 patients (96.2%). Overall, the functional neurological status of patients improved after microsurgical dissection at the time of discharge from the hospital and at follow-up. At 6 months, 64 patients (81.0%) were improved relative to their preoperative condition and 14 patients (17.7%) were unchanged. Good outcomes (modified Rankin Scale score ≤ 2, living independently) were achieved in 77 patients (97.4%). Multivariate analysis of demographic and surgical factors revealed that preoperative functional status was the only predictor of postoperative modified Rankin Scale score (OR 4.6, p = 0.001). Six patients (7.6%) had transient worsening of neurological examination after surgery, and 1 patient (1.3%) was permanently worse. There was no surgical mortality.

CONCLUSIONS

The authors present a system of 13 microsurgical approaches to 6 location targets with 4 general trajectories to facilitate safe access to supratentorial CMs in eloquent brain regions. Favorable neurological outcomes following microsurgical resection justify an aggressive surgical attitude toward these lesions.