Graepel, Stephen

BACKGROUND Hypertrophic olivary degeneration (HOD) is a rare form of transsynaptic degeneration caused by disruption of the dentato-rubro-olivary pathway (Guillain-Mollaret triangle). It is most described following surgical intervention or acute hemorrhagic injury affecting that pathway. However, longitudinal imaging documenting the natural progression of HOD in patients with brainstem cerebral cavernous malformations (CCMs) remains sparsely described at the individual patient level. OBSERVATIONS The authors present the case of a 70-year-old woman with a pontine CCM followed longitudinally over 4 years. Initial imaging demonstrated a right-sided pontine lesion with unilateral HOD in the absence of symptoms. Over time, the CCM enlarged and extended across the midline, coinciding with the development of bilateral HOD and delayed onset of gait imbalance and palatal myoclonus. No surgical intervention was performed. LESSONS In this case, the radiographic evolution from unilateral to bilateral involvement occurred concurrently with the delayed clinical manifestation of HOD. https://thejns.org/doi/10.3171/CASE26577

BACKGROUND AND OBJECTIVES: Contralateral transfalcine approaches are widely used for interhemispheric/mesial cortical pathologies, even those extending beyond 2 cm lateral from the midline. Nevertheless, the superior limit of contralateral exposure through this approach is not defined. This anatomic study aims to characterize the maximal superior and lateral limits of contralateral exposure using a contralateral transfalcine approach. METHODS: Interhemispheric approaches in the anterior, middle, and posterior-thirds of the interhemispheric fissure were performed in 10 cadaveric head specimens. Rectangular falcine incisions were made and carried maximally superiorly. The contralateral hemisphere was maximally laterally resected from the superior point of visualization down to the level of the corpus callosum. Distances between the most superior point of visualization of the contralateral hemisphere and the superficial point of its cortex and between the midline and the most lateral point of visualization at the level of the corpus callosum were measured and are reported as averages. RESULTS: At the anterior-third of the interhemispheric fissure, the superior point of visualization was 4.8 mm inferior to the cortex. The lateral distance of visualization at the genu of the corpus callosum was 22.9 mm. At the middle-third, the superior point of visualization was 9.7 mm inferior to the cortex. The lateral distance visualized at the body of the corpus callosum was 22.4 mm. At the posterior-third, the superior point visualization of the mesial contralateral hemisphere was 12.6 mm inferior to the cortex. The lateral distance visualized at the splenium of the corpus callosum was 21.3 mm. CONCLUSION: Using the contralateral transfalcine approach, the superior limit of contralateral exposure progressively decreases more posteriorly along the interhemispheric corridor—ranging from 4.8 mm inferior to the cortex in the anterior-third to 12.6 mm inferior to the cortex in the posterior-third. The contralateral optimal view of exposure increases deeper along the interhemispheric corridor.

BACKGROUND AND OBJECTIVES: Contemporary skull base surgeons must understand transcranial and endoscopic endonasal approaches to the petrous apex (PA). We provide an anatomic overview and comparison of main approaches to the PA through illustrative anatomic dissections. METHODS: On 10 sides of 5 specimens, transcranial approaches to the PA including the anterior petrosal, transcochlear, and retrosigmoid with suprameatal extension were performed. For endoscopic endonasal approaches, the transclival approach was performed in the midline of 5 specimens and its contralateral transmaxillary extension was performed on 10 sides. RESULTS: The anterior petrosal approach offers an anterolateral view of the PA bounded by petrous ridge posteromedially, internal auditory canal posterolaterally, greater superficial petrosal nerve anterolaterally, and lateral boundary of cranial nerve V, the Gasserian ganglion, and V3 anteromedially; it exposes the middle fossa and, once the PA is removed, the superomedial cerebellopontine angle. The transcochlear approach affords a lateral view of the PA defined medially and inferiorly by inferior petrosal sinus, posteriorly by posterior fossa dura, anteriorly by the petrous internal carotid artery, and superiorly by the superior petrosal sinus and middle fossa dura. Through a retrosigmoid approach, the PA is bounded by the superior petrosal sinus superiorly, the sagittal plane of cranial nerve VI medially, and the axial and sagittal plane of the internal auditory canal porus inferiorly and laterally, respectively. It affords a panoramic view of the posterior fossa and access to Meckel's cave after PA drilling. Endoscopic endonasal approaches target the anteromedial PA, and it is demarcated by a triangle consisting of cranial nerve VI posterolaterally, the paraclival segment of the internal carotid artery anteriorly, and the petroclival synchondrosis inferiorly and medially. The addition of the contralateral transmaxillary approach enhances lateral access up to the internal auditory canal. CONCLUSION: We provide a comprehensive overview of the main approaches to the PA through illustrative anatomic dissections and representative cases.

OBJECTIVE Lesions of the cerebellopontine angle (CPA) and petroclival region represent a challenging surgical target due to the complex anatomy of the involved neurovascular structures. In this scenario, cranial nerve (CN) VI is particularly exposed to potential injuries due to its deep-seated location and absence of a bony foramen that serves as a reference of its most distal cisternal point, especially when it is encased or displaced by large lesions. This study aimed to provide reliable operative guidance for preventing injuries to CN VI during the retrosigmoid approach to address CPA and petrotentorial lesions. METHODS Four formalin-fixed, latex-injected anatomical specimens were dissected to highlight and investigate the relevant anatomy of the CPA and petroclival region during the retrosigmoid approach. Additionally, 50 sides of noninjected formalin-fixed specimens were dissected for morphometric evaluation. Correlations between the petrotentorial junction (PTJ), porus acusticus (PA), and trigeminal impression (TI) with the entry point of CN VI into Dorello’s canal were evaluated. An illustrative clinical case and a 3D anatomical model generated through the photogrammetry scanning technique were described. RESULTS In the sagittal plane, CN VI entrance into Dorello’s canal was found in a trajectory parallel to the PTJ, passing through the inferior aspect of the PA and 21.5 ± 1.3 mm anteriorly. In the coronal plane, the entry point of CN VI into Dorello’s canal was estimated at 6.2 ± 1.2 mm from the anterior edge of the TI in a trajectory perpendicular to the PTJ in 47 (81%) specimens. CONCLUSIONS The obtained results demonstrated two surgical strategies to locate Dorello’s canal within the retrosigmoid route: 1) approximately 20 mm anterior along the inferior edge of the PA parallel to the PTJ; and 2) approximately 6 mm inferior to the anterior edge of the TI, perpendicular to the PTJ. The defined operative strategies provide reliable anatomical guidance to locate the entrance of CN VI into Dorello’s canal within the retrosigmoid route, potentially reducing the risk of abducens nerve palsy and improving patient outcomes.

OBJECTIVE Hundreds of thousands of Americans undergo decompression for lumbar spinal stenosis annually. The mild (minimally invasive lumbar decompression) procedure was developed as a potentially less invasive alternative to open decompression; however, much of the evidence has been gathered from industry-sponsored studies. The present study sought to compare real-world clinical outcomes between the mild procedure and open decompression for lumbar spinal stenosis. METHODS All patients who underwent the mild procedure at a single-institution, multisite, tertiary care center from 2005 to October 2024 were included. One-to-one propensity score matching was used to identify patients who underwent open decompression at the same institution, with age, sex, smoking, and comorbidities as covariates. Primary outcomes were change in pain on the numeric rating scale (NRS), surgical reoperation, and perioperative complications. For pain, the minimal clinically important difference (MCID) was defined as a 30% improvement in NRS score. RESULTS A total of 175 patients who underwent the mild procedure (mean age 76.3 ± 8.7 years; 44.6% female) were matched to 175 patients treated with open decompression (mean age 75.4 ± 8.7 years; 44.0% female). Among patients with at least 60 days of follow-up, those treated with open decompression were more likely to achieve the MCID for pain (43.1% vs 22.2%, p < 0.001). Patients treated with mild were more likely to require reoperation (46.2% vs 29.3%, p = 0.008). Those who underwent the mild procedure experienced lower rates of durotomies (0% vs 2.9%, p = 0.024) but had higher rates of neurological deficits (6.3% vs 0.6%, p = 0.003). CONCLUSIONS For patients with symptomatic lumbar stenosis, those who underwent open decompression were more likely to achieve pain improvement and less likely to require reoperation compared with those who underwent the mild procedure.

OBJECTIVE The implementation of robotics and spinal anesthesia (SA) in spine surgery is rapidly expanding, offering significant benefits for an increasingly complex and aging patient population with degenerative spinal disease. Here, the authors present the largest cohort to date evaluating the combined use of these two techniques in minimally invasive (MIS) transforaminal lumbar interbody fusion (TLIF). METHODS The authors retrospectively analyzed surgical outcomes of a series of patients who underwent robot-assisted (RA)–MIS TLIF under SA and general anesthesia (GA) at their institution from 2018 to 2024. Primary outcomes included operative times and postoperative pain intensity. Secondary outcomes included estimated blood loss, intraoperative complications, postoperative functional status, length of stay (LOS), and discharge status. To address potential confounders, a 1:1 propensity score–matching and regression analysis was implemented. Statistical analyses were conducted using Python. RESULTS A total of 209 patients underwent RA-MIS TLIF, with 31 (14.83%) receiving SA and 178 (85.17%) GA. After propensity score matching, the SA cohort demonstrated significantly shorter median total operating room (OR) time, total procedure time, time from entering the OR to skin incision, and time from closure to leaving the OR (all p < 0.01). Additionally, postoperative pain scores were significantly lower (p < 0.01), and LOS was significantly shorter (p < 0.01) in the SA cohort. Regression analysis, adjusting for potential confounders, further supported these findings. CONCLUSIONS RA-MIS TLIF fusion under SA is a safe and effective approach that significantly reduces operative time, postoperative pain, and hospital LOS in patients undergoing surgery for degenerative lumbar spine disease.

In this video, the authors present the microsurgical treatment of a superior petrosal dural arteriovenous fistula (dAVF) associated with a symptomatic hemorrhagic brainstem cavernous malformation in a 38-year-old male. The patient underwent a retrosigmoid craniotomy for cavernoma evacuation and fistula disconnection. Intraoperative indocyanine green angiography revealed cortical venous reflux not evident on catheter angiography, prompting reclassification to a higher-grade fistula. Postoperatively, the patient returned to neurological baseline, and follow-up imaging confirmed complete fistula obliteration, cavernoma resection, and new appearance of a developmental venous anomaly (DVA). This case highlights the dynamic nature of dAVF venous drainage and illustrates the rare co-occurrence of dAVF, DVA, and brainstem cavernoma. The video can be found here: https://stream.cadmore.media/r10.3171/2025.7.FOCVID2553

ABSTRACT Objective Sacrifice of pterygopalatine fossa (PPF) neurovascular structures during endoscopic endonasal transpterygoid approach (EETPA) may impact a patient's comorbidity. We present anatomical and surgical techniques for maximizing PPF transposition while preserving its neurovascular structures through orbito‐pterygo‐sphenoidal (OPS) ligament release and descending palatine canal (DPC) decompression. Methods The EETPA was performed on six specimens. Two measurements were obtained to assess PPF transposition: (1) Inferior transposition (distance between the superior margins of the base of the pterygoid process and PPF); (2) lateral transposition (distance from Eustachian tube lateral margin to PPF medial margin). Results After incising the OPS ligament, a mean gain of PPF inferior transposition of 7 mm (4–11 mm, p = 0.03) was observed, with a total inferior transposition of 12 mm (6–15 mm). Subsequently, the posterior half of the inferior turbinate was removed and the DPC was decompressed, with a mean gain of PPF lateral transposition of 12 mm (range 8–15 mm, p = 0.01). Conclusion The OPS ligament release offers a significant advantage for the PPF inferior transposition, allowing access to the inferolateral recess of the sphenoid sinus, cavernous sinus, and paramedian middle cranial fossa, while the DPC decompression provides a significant advantage for the PPF lateral transposition, granting access to the Eustachian tube and ITF. Level of Evidence N/A.

BACKGROUND AND OBJECTIVES: This study aimed to evaluate predictors of hypertrophic olivary degeneration (HOD) in patients with brainstem cerebral cavernous malformations (CCMs) and to examine its association with functional outcomes. METHODS: A cohort of 120 patients with brainstem CCM was analyzed using prospectively collected registry data and retrospective chart reviews. Demographic, clinical, radiological, and surgical data were evaluated. Predictors of HOD and poor functional outcomes were identified through univariate and multivariate analyses. RESULTS: The cohort included 54 females (45.0%), with a mean age at diagnosis of 43.8 years (SD = 16.5). Symptomatic hemorrhage was present in 70.8% of patients at diagnosis, and 28.3% underwent surgical intervention. Radiographic HOD was observed in 20% of patients (n = 24), with 87% of cases involving lesions within the Guillain–Mollaret triangle (GMT). Larger lesion size (odds ratio [OR] = 1.09, 95% CI: 1.01-1.19, P = .027), pontine location (OR = 19.81, P = .006), and GMT involvement (OR = 25.24, P < .001) were significantly associated with HOD. Repeated symptomatic hemorrhage and surgery, including the extent of resection, did not predict the development of HOD. Patients with HOD had worse functional outcomes at last follow-up ( P = .012), with GMT involvement remaining the sole independent predictor of mRS ≥3 (OR = 3.44, P = .040). CONCLUSION: HOD reflects trans-synaptic degeneration within the GMT and is strongly associated with lesion location and size. It serves as a radiological marker of cumulative damage to the brainstem. Preoperative imaging and risk stratification focusing on GMT involvement are critical for guiding management and counseling patients with brainstem CCM.