A taxonomy for brainstem cavernous malformations: subtypes of pontine lesions. Part 1: basilar, peritrigeminal, and middle peduncular

Novel classification and microsurgical anatomy of the basilar artery: a cadaveric study

PURPOSE

The trunk of the BA remains underrepresented in microsurgical studies. This study aims to address this gap by providing a detailed review of the BA's microsurgical anatomy, proposing a novel segmental classification of the artery and the significance of each segment in various surgical pathologies and approaches.

METHODS

A total of 20 cadaveric adult brain specimens were meticulously examined under high magnification, following Institutional Review Board approval. The dissection focused on the BA and its branches, with morphometric data collected, including dimensions and anatomical variations.

RESULTS

This study included 20 specimens. A novel classification was proposed base on the blood flow direction, including three segments. The inferior segment extended from the junction of the VA to the origin of the most rostral collateral artery, averaging 3.55 mm in diameter and lengths between 9.0 and 17.1 mm, with 3 to 4 caudal perforators. The middle segment, which ranged from the inferior border of the anterior inferior cerebellar artery (AICA) to the origin of the superior cerebellar artery, measured 3.44 mm in diameter and 15.2 mm in length, featuring 5-6 middle perforating branches. The superior segment ended at the bifurcation of the BA, with an average diameter of 4.2 mm and a length of 3.6 mm. The overall BA length averaged 30.7 mm, with a range of 23.5-38.2 mm.

CONCLUSION

A comprehensive understanding of the origin, course, branches and segments of the BA is crucial for mitigating vascular complications during both open and endovascular surgical procedures.

Development and Validation of a Supplementary Grading Scale for Outcomes of Brainstem Cavernous Malformations

BACKGROUND

Surgical risk assessment is intriguing for clinical decision-making of brainstem cavernous malformation (BSCM) treatment. While the BSCM grading scale, encompassing size, developmental venous anomaly, crossing axial midpoint, age, and timing of intervention, is increasingly utilized, the clinical relevance of neurological fluctuation and recurrent hemorrhage has not been incorporated. This study aimed to propose a supplementary grading scale with enhanced predictive efficacy.

METHODS

Using a retrospective nationwide registry of consecutive patients with BSCMs undergoing surgery in China from March 2011 to May 2023, a new supplementary BSCM grading scale was developed from a derivative cohort of 260 patients and validated in an independent concurrent cohort of 67 patients. The primary outcome was unfavorable neurological function (modified Rankin Scale score >2) at the latest follow-up. The performance of the supplementary grading system was evaluated for discrimination, calibration, and clinical utility and further compared with its original counterpart.

RESULTS

Over a follow-up of at least 6 months after surgery, the unfavorable outcomes were 31% in the overall cohort (101/327 patients). A preoperative motor deficit (odds ratio, 3.13; P=0.001), recurrent hemorrhage (odds ratio, 3.05; P<0.001), timing of intervention (odds ratio, 7.08; P<0.001), and crossing the axial midpoint (odds ratio, 2.57; P=0.006) were associated with the unfavorable outcomes and composed the initial Huashan grading variables. A supplementary BSCM grading system was subsequently developed by incorporating the Huashan grading variables into the original BSCM grading scale. The predictive capability of the supplementary scale was consistently superior to the original counterpart in either the derivative cohort (area under the receiver operating characteristic curve, 0.74 [95% CI, 0.68-0.80] for the supplementary versus 0.68 [95% CI, 0.61-0.74] for the original) or the validation cohort (0.75 [95% CI, 0.62-0.87] versus 0.64 [95% CI, 0.48-0.81]).

CONCLUSIONS

This study highlights the neurological relevance of BSCM hemorrhage in surgical risk assessment. Via compositing preoperative motor function and recurrent hemorrhages, a supplementary grading scale may improve a dynamic risk assessment for clinical decisions in the management of BSCMs.

Intraparenchymal Chordoma in the Brain Stem: A Review of Surgical Management and Case Highlight

We present a rare case of an intraparenchymal chordoma in the brain stem of a 69-year-old male with a history of multiple chordoma recurrences. Chordomas are uncommon tumors that originate from notochordal remnants, with intraparenchymal presentations in the brain stem being particularly rare. A 69-year-old male with a history of clival chordoma three years after primary endoscopic resection and adjuvant proton-beam radiotherapy and a recurrence one year postoperatively for which he underwent a second surgery, presented with severe headaches, weakness, diaphoresis, and difficulty ambulating. Head CT in the ER revealed a 2.7 x 3.5 cm hyperdense lesion in the pons, indicating acute hemorrhage. Magnetic resonance imaging (MRI) suggested a hemorrhagic radiation-induced cavernoma. A right retrosigmoid craniotomy was performed, and the lesion was resected without major complications. Final pathology reported an intraparenchymal hemorrhagic chordoma. To our knowledge, this is the first case of intra-axial chordoma, particularly in the brain stem. It highlights the importance of considering intraparenchymal chordoma on the differential when evaluating for recurrence versus other treatment-induced pathologies and changes. This may prompt the neurosurgeon to reconsider treatment options and weigh the risks of watchful waiting versus biopsy or even aggressive surgical management.

A novel method of neurophysiological brainstem mapping in neurosurgery

BACKGROUND

Brainstem mapping with electrical stimulation allows functional identification of neural structures during resection of deep lesions. Single pulses or train of pulses are delivered to map cranial nerves and corticospinal tracts, respectively.

NEW METHOD

We introduce a hybrid stimulation technique for mapping the brainstem. The stimulus consists of an electrical single pulse followed by a short train of 3-5 pulses at 500 Hz, at an interval of 60-75 ms. The responses to this stimulation pattern are recorded from appropriate cranial and limb muscles.

RESULTS

Both the single pulse and the short train elicit electromyographic responses when motor fibers or motor nuclei of the cranial nerves are stimulated. Responses to the train but not to the preceding single pulse indicate activation of the descending motor tracts, in the mesencephalon and the pons. Conversely, in the medulla, limb responses to stimulation of the corticospinal tracts are elicited by a single pulse. Identification of the extra and intra-axial courses of the trigeminal motor and sensory fibers is possible by recording responses from the masseter and the tongue muscles.

COMPARISON WITH EXISTING METHOD(S)

To date, either a pulse or a train is delivered during brainstem mapping, switching from one to the other modality according to the expected target structure. This procedure can be time-consuming and may even lead to false negative responses to the stimulation, eventually leading to inaccurate neurosurgical procedures.

CONCLUSIONS

The novel hybrid pulse-train technique enhances the advantage of brainstem mapping procedure, minimizing pitfalls and improving patient safety.

Mandibular Fossa Approach to Petroclival and Anterior Pontine Lesions

Objective  To describe the anatomy related to a novel approach to the petroclival region through the mandibular fossa for the treatment of petroclival and anterior pontine lesions. Design  Five dry skulls were examined for surgical approach. Three adult cadaveric heads underwent bilateral dissection. One cadaveric head was evaluated with computed tomography after dissection. Setting  This study was performed in an academic medical center. Participants  Neurosurgical anatomy researchers performed this study using dry skulls and cadaveric heads. Main Outcome Measurements  This was a proof-of-concept anatomical study. Results  The mandibular fossa approach uses a vertical preauricular incision above the facial nerve branches. Removal of the temporomandibular joint exposes the mandibular fossa. The anterior boundary is the mandibular nerve at the foramen ovale, and the posterior boundary is the jugular foramen. The chorda tympani, eustachian tube, and tensor tympani muscle are sectioned. The carotid artery is transposed out of the petrous canal, and a petrosectomy is performed from Meckel's cave to the foramen magnum and anterior occipital condyle. Dural opening exposes the anterior pons, vertebrobasilar junction, bilateral vertebral arteries, and the ipsilateral anterior and posterior inferior cerebellar arteries. At completion, the temporomandibular joint is reconstructed with a prosthetic joint utilizing a second incision along the mandible. Conclusions  The mandibular fossa approach is a new trajectory to the petroclival region and the anterior pons. It combines the more anterior angle of endoscopic approaches along with the enhanced control of open approaches. Further study is necessary before this approach is used clinically.

Recurrent haemorrhagic pontine cavernoma resection via a retrosigmoid microsurgical approach

BACKGROUND

Brainstem cavernomas occasionally require surgical treatment. Appropriate patient selection and thorough understanding of the anatomy and technical nuances involved in microsurgical resection is a pre-requisite in undertaking these challenging cases.

CASE DESCRIPTION

We present a video case of a patient with a recurrent haemorrhagic pontine cavernoma. A step-by-step commentary of surgical footage is provided along with clinical, anatomical and technical learning points pertinent to the safe surgical management of these lesions.

Long-term functional outcomes and complications of microsurgical resection of brainstem cavernous malformations: a systematic review and meta-analysis

Brainstem cavernous malformations (CMs) encompass up to 20% of all intracranial CMs and are considered more aggressive than cerebral CMs because of their high annual bleeding rates. Microsurgical resection remains the primary treatment modality for CMs, but long-term functional outcomes and complications are heterogenous in the literature. The authors performed a systematic review on brainstem CMs in 4 databases: PubMed, EMBASE, Cochrane library, and Google Scholar. We included studies that reported on the long-term functional outcomes and complications of brainstem CMs microsurgical resection. A meta-analysis was performed and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The search yielded 4781 results, of which 19 studies met our inclusion criteria. Microsurgery was performed on 940 patients (mean age 35 years, 46.9% females). Most of the brainstem CMs were located in the pons (n = 475). The pooled proportions of improved, stable, and worsened functional outcomes after microsurgical resection of brainstem CMs were 56.7% (95% CI 48.4-64.6), 28.6% (95% CI 22.4-35.7), and 12.6% (95% CI 9.6-16.2), respectively. CMs located in the medulla were significantly (p = 0.003) associated with a higher proportion of improved outcome compared with those in the pons and midbrain. Complete resection was achieved in 93.3% (95% CI 89.8-95.7). The immediate postoperative complication rate was 37.2% (95% CI 29.3-45.9), with new-onset cranial nerve deficit being the most common complication. The permanent morbidity rate was 17.3% (95% CI 10.5-27.1), with a low mortality rate of 1% from the compiled study population during a mean follow-up of 58 months. Our analysis indicates that microsurgical resection of brainstem CMs can result in favorable long-term functional outcomes with transient complications in the majority of patients. Complete microsurgical resection of the CM is associated with a lower incidence of CM hemorrhage and the morbidity related to it.

Five-year symptomatic hemorrhage risk of untreated brainstem cavernous malformations in a prospective cohort

Hemorrhage of brainstem cavernous malformation (CM) would cause various symptoms and severe disability. The study aimed to elaborate on the 5-year actuarial cumulative hazard of symptomatic hemorrhage. Patients diagnosed in our institute between 2009 and 2013 were prospectively registered. All clinical data were obtained, follow-up was performed, and risk factors were evaluated. Four hundred sixty-eight patients (217 female, 46.4%) were included in the study with a median follow-up duration of 79.0 months. A total of 137 prospective hemorrhages occurred in 107 patients (22.9%) during 1854.0 patient-years. Multivariate Cox analysis found age ≥ 55 years (hazard ratio (HR) 2.166, p = 0.002), DVA (HR 1.576, p = 0.026), superficial-seated location (HR 1.530, p = 0.047), and hemorrhage on admission (HR 2.419, p = 0.026) as independent risk factors for hemorrhage. The 5-year cumulative hazard of hemorrhage was 30.8% for the overall cohort, 47.8% for 60 patients with age ≥ 55 years, 43.7% for 146 patients with DVA, 37.9% for 272 patients with superficial-seated lesions, and 37.2% for 341 patients with hemorrhage on admission. As a stratified analysis, within subcohort of 341 patients with a hemorrhagic presentation, age ≥ 55 years (HR 3.005, p < 0.001), DVA (HR 1.801, p = 0.010), and superficial-seated location (HR 2.276, p = 0.001) remained independently significant. The 5-year cumulative hazard of hemorrhage was 52.0% for 119 patients with both DVA and hemorrhagic presentation. The 5-year cumulative hemorrhagic risk was 30.8% and was higher in subgroups if harboring risk factors that helped to predict potential hemorrhagic candidates and were useful for treatment decision-making.Clinical Trial Registration-URL: http://www.chictr.org.cn Unique identifier: ChiCTR-POC-17011575.