The Mini-Craniotomy for cSDH Revisited: New Perspectives.

Background: Chronic subdural hematomas (cSDH) are increasingly prevalent worldwide with the increased aging population and anticoagulant use. Different surgical, medical, and endovascular treatments have had varying success rates. Primary neurosurgical interventions include burr hole drainage of the cSDH and mini-craniotomies/craniotomies with or without fenestration of the inner membrane. A key assessment of the success or failure of cSDH treatments has been symptomatic recurrence rates which have historically ranged from 5 to 30%. Pre-operative prediction of the inner subdural membrane by CT scan was used to guide our decision to perform mini-craniotomies. Release of the inner membrane facilitates the expansion of the brain and likely improves glymphatic flow. Methods: Consecutive mini-craniotomies (N = 34) for cSDH evacuation performed by a single neurosurgeon at a quaternary academic medical center/Level I trauma center from July 2018-September 2020 were retrospectively reviewed. Patient characteristics [age, gender, presenting GCS, GOS, initial CTs noting the inner subdural membrane, midline shift (MLS), cSDH width, inner membrane fenestration, cSDH recurrence, post-operative seizures, infections, length of stay] were extracted from the EMR. Results: Twenty nine patients had mini-craniotomies as primary treatment of the cSDH. Mean age = 68.9 ± 19.7 years (range 22-102), mean pre-operative GCS = 14.5 ± 1.1, mean MLS = 6.75 ± 4.2 mm, and mean maximum thickness of cSDH = 17.7 ± 6.0 mm. Twenty four were unilateral, five bilateral, 34 total craniotomies were performed. Thirty three had inner membrane signs on pre-operative head CTs and an inner subdural membrane was fenestrated in all cases except for the one craniotomy that didn't show these characteristic CT findings. Mean operating time = 79.5 ± 26.0 min. Radiographic and clinical improvement occurred in all patients. Mean improvement in MLS = 3.85 ± 2.69. There were no symptomatic recurrences, re-operations, surgical site infections, or deaths during the 6 months of follow-up. One patient was treated for post-operative seizures with AEDs for 6 months. Conclusion: Pre-operative CT scans demonstrating inner subdural membranes may guide one to target the treatment to allow release of this tension band. Mini-craniotomy with careful fenestration of the inner membrane is very effective for this. Brain re-expansion and re-establishment of normal brain interstitial flow may be important in long term outcomes with cSDH and may be related to the recent interests in brain glymphatics and dural lymphatics.

Alzheimer's disease: The role for neurosurgery.

Dementia, most commonly caused by Alzheimer's disease (AD), affects approximately 35 million people worldwide, with the incidence expected to increase as the population ages. After decades of investigation, AD is now understood to be a complex disease that affects behavior and cognition through several mechanisms: Disrupted neuronal communication, abnormal regional tissue metabolism, and impaired cellular repair. Existing therapies have demonstrated limited efficacy, which has spurred the search for specific disease markers and predictors as well as innovative therapeutic options. Deep brain stimulation (DBS) of the memory circuits is one such option, with early studies suggesting that modulation of neural activity in these networks may improve cognitive function. Encapsulated cell biodelivery (ECB) is a device that delivers nerve growth factor to the cholinergic basal forebrain to potentially improve cognitive decline in AD patients. This review discusses the pathogenesis of AD, novel neuroimaging and biochemical markers, and the emerging role for neurosurgical applications such as DBS and ECB.

Eyelid apraxia associated with deep brain stimulation of the periaqueductal gray area.

We report a patient with eyelid apraxia following deep brain stimulation of the periaqueductal gray area. Based on the position of our electrode, we argue that the phenomenon is linked to inhibition of the nearby central caudal nucleus of the oculomotor nucleus by high frequency stimulation.

Deep brain stimulator-induced diaphoresis in Parkinson's disease patients.

We report an unusual finding of bilateral facial and corporeal diaphoresis and sensation of heat during deep brain stimulation in two patients. Stimulation of the hypothalamospinal tract located medial to the subthalamic nucleus is likely to be responsible for this side effect.

Clinical functional anatomy of the pterygopalatine ganglion, cephalgia and related dysautonomias: A review.

The purpose of this article is to explain the anatomy of the pterygopalatine ganglion (PPG), its location in the pterygopalatine fossa (PPF) in the skull, and the relationship it has to the Vidian nerve terminal branches and the fifth cranial nerve. An overview of the neuro-anatomical/clinical correlations, a spectrum of pathologies affecting the seventh cranial nerve and some therapies both medical and surgical are noted. The focus is the pterygopalatine region with discussion of the proximal courses of the seventh and fifth cranial nerves and their pathological processes. The ganglion is used as an example of neuro-anatomical model for explaining cluster headaches (CH). Radiological correlation is included to clarify the location of the PPF and its clinical importance.

The extended subtemporal transtentorial approach: the impact of trochlear nerve dissection and tentorial incision.

The subtemporal transtentorial approach provides excellent exposure of the incisural space. Incision of the tentorium improves access to the interpeduncular cistern, basilar artery, and rostral ventral pons. Description of the starting and termination points of the tentorial incision has varied greatly. We assessed the impact on surgical exposure of freeing the trochlear nerve (TN) from its dural canal (DC) in addition to dividing and retracting the tentorium. A subtemporal approach was performed on 10 hemispheres of cadaveric specimens. Following exposure of the middle tentorial incisura, the TN is dissected from its DC over a few millimeters. Two retraction sutures are placed along the tentorial edge, posterior to the TN entrance in its DC. The tentorial incision is started between the sutures. Dissection of TN from its DC continues for a short distance. The tentorial incision is extended straight up towards the superior petrosal sinus. Dissection of the TN DC continues anteriorly, up to its entry into the cavernous sinus. The tentorial incision can then be extended, just over the entrance to Meckel's cave, and the flap reflected far anterolateraly. Using this technique, the exposure of the interpeduncular cistern and its content increased by a mean of 8.2 mm (standard deviation [SD] 3.9 mm) in the anteroposterior axis and by 5.5mm (SD 1.9 mm) in the rostrocaudal axis. Tentorial incision following dissection of the TN from its DC optimizes reflection of the tentorium flap anterolateraly, maximizes the exposure, and improves lighting and visibility as well as maneuverability within the interpeduncular and rostral pre-pontine cisterns.

Advances in the biology of cerebral cavernous malformations.

OBJECT: To provide a review of current, high-impact scientific findings pertaining to the biology of cerebral cavernous malformations (CCMs). METHODS: A comprehensive literature review was conducted using PubMed to examine the current literature regarding the molecular biology and pathophysiology of CCMs. RESULTS: In this literature review, a comprehensive approach is taken to review the current scientific status of CCMs. This includes discussion of molecular biology and animal models, ultrastructure and angioarchitectural features and immunological methods and hypotheses. CONCLUSIONS: Studies examining the molecular biology of CCMs have shown that genes involved in angiogenesis, blood-brain barrier formation, cell size regulation, vascular permeability and apoptosis play critical roles in the ontogeny of this disease. In vivo work suggests the likelihood of a "two-hit mechanism" resulting in somatic mosaicism and biallelic loss of angiogenic genes. The etiological effects of angioarchitecture and immune response within these lesions further complicate the pathophysiology. Future treatment endeavors will necessitate exploitation of the multiple facets of CCM formation to maximize success at CCM prevention or obliteration.

Cerebral arteriovenous malformations. Part 1: cellular and molecular biology.

OBJECT: The scientific understanding of the nature of arteriovenous malformations (AVMs) in the brain is evolving. It is clear from current work that AVMs can undergo a variety of phenomena, including growth, remodeling, and/or regression-and the responsible processes are both molecular and physiological. A review of these complex processes is critical to directing future therapeutic approaches. The authors performed a comprehensive review of the literature to evaluate current information regarding the genetics, pathophysiology, and behavior of AVMs. METHODS: A comprehensive literature review was conducted using PubMed to reveal the molecular biology of AVMs as it relates to their complex growth and behavior patterns. RESULTS: Growth factors involved in AVMs include vascular endothelial growth factor, fibroblast growth factor, transforming growth factor beta, angiopoietins, fibronectin, laminin, integrin, and matrix metalloproteinases. Conclusions Understanding the complicated molecular milieu of developing AVMs is essential for defining their natural history. Growth factors, extracellular matrix proteins, and other molecular markers will be the key to unlocking novel targeted drug treatments for these brain malformations.

Cerebral arteriovenous malformations. Part 2: physiology.

OBJECT: The scientific understanding of the nature of arteriovenous malformations (AVMs) in the brain is evolving. It is clear from current work that AVMs can undergo a variety of phenomena, including growth, remodeling, and/or regression-and the responsible processes are both molecular and physiological. A review of these complex processes is critical to directing future therapeutic approaches. The authors performed a comprehensive review of the literature to evaluate current information regarding the genetics, pathophysiology, and behavior of AVMs. METHODS: A comprehensive literature review was conducted using PubMed to reveal the angioarchitecture and cerebral hemodynamics of AVMS as they relate to lesion development. RESULTS: Feeding artery pressures, brain AVM compartmentalization, venous drainage, flow phenomena, and vascular steal are discussed. CONCLUSIONS: The dynamic nature of brain AVMs is at least in part attributable to hemodynamic and flow-related phenomena. These forces acting on an evolving structure are critical to understanding the challenges in endovascular and surgical therapy. As knowledge in this field continues to progress, the natural history and predicted behavior of these AVMs will become more clearly elucidated.

Stereotactic coordinates associated with facial musculature contraction during high-frequency stimulation of the subthalamic nucleus.

OBJECT: High-frequency stimulation of the subthalamic nucleus (STN) in patients with parkinsonian symptoms is often used to ameliorate debilitating motor symptoms associated with this condition. However, individual variability in the shape and orientation of this relatively small nucleus results in multiple side effects related to the spread of electrical current to surrounding structures. Specifically, contraction of the muscles of facial expression is noted in a small percentage of patients, although the precise mechanism remains poorly understood. METHODS: Facial muscle contraction was triggered by high-frequency stimulation of 49 contacts in 18 patients undergoing deep brain stimulation of the STN. The mean coordinates of these individual contacts relative to the anterior commissure-posterior commissure midpoint (also called the midcommissural point) were calculated to determine the location or structure(s) most often associated with facial contraction during physiological macrostimulation. RESULTS: The x, y, and z coordinates associated with contraction of the facial musculature were found to be 11.52, 1.29, and 1.15 mm lateral, posterior, and inferior to the midcommissural point, respectively. This location, along the lateral-anterior-superior border of the STN, may allow for the spread of electrical current to the fields of Forel, zona incerta, and/or descending corticospinal/corticobulbar tracts. Because stimulation of corticobulbar tracts produces similar findings, these results are best explained by the spread of electrical current to nearby internal capsule axons coursing lateral to the STN. CONCLUSIONS: Thus, if intraoperative deep brain stimulation lead testing results in facial musculature contraction, placement of the electrode in a more medial, posterior position may reduce the amount of current spread to corticobulbar fibers and resolve this side effect.

Endonasal versus supraorbital keyhole removal of craniopharyngiomas and tuberculum sellae meningiomas.

OBJECTIVE: Endonasal and supraorbital "eyebrow" craniotomies are increasingly being used to remove craniopharyngiomas and tuberculum sellae meningiomas. Herein, we assess the relative advantages, disadvantages, and selection criteria of these 2 keyhole approaches. METHODS: All consecutive patients who had endonasal or supraorbital removal of a craniopharyngioma or tuberculum sellae meningioma were analyzed. RESULTS: Of 43 patients, 22 had a craniopharyngioma (18 endonasal, 4 supraorbital), and 21 had a meningioma (12 endonasal, 7 supraorbital, 2 both routes); 33% had prior surgery. Craniopharyngiomas were primarily retrochiasmal in location in 78% of endonasal cases versus 25% of supraorbital cases (P = 0.08). Meningiomas were larger when approached by the supraorbital route versus the endonasal route (33 +/- 10 versus 25 +/- 8 mm, respectively; P = 0.008). Endoscopy was used in 84% of endonasal approaches and in 31% of supraorbital approaches (P = 0.001). Of patients having first-time surgery for a craniopharyngioma (n = 14) or meningioma (n = 15), total/near total removal was achieved in 83% and 80% of patients by the endonasal route and in 50% and 80% of patients by the supraorbital route, respectively. Vision improved in 87% and 70% of patients who had surgery by an endonasal versus supraorbital route, respectively (P = 0.3). Visual deterioration occurred in 2 patients with meningiomas, 1 by endonasal (7%), and 1 by supraorbital (11%) removal. The endonasal approach was associated with a higher rate of postoperative cerebrospinal fluid leaks (16 versus 0%; P = 0.3), 4 of 5 of which occurred in patients with meningioma. CONCLUSION: The endonasal route is preferred for removal of most retrochiasmal craniopharyngiomas, whereas the supraorbital route is recommended for meningiomas larger than 30 to 35 mm or with growth beyond the supraclinoid carotid arteries. For smaller midline tumors, either approach can be used, depending on surgeon experience and tumor anatomy. Compared with traditional craniotomies, the major limitation of both approaches is a narrow surgical corridor. The endonasal approach has the added challenges of restricted lateral suprasellar access, a greater need for endoscopy, and a more demanding cranial base repair.

A short trapezoidal speculum for suprasellar and infrasellar exposure in endonasal transsphenoidal surgery.

OBJECTIVE: A key limitation of the transsphenoidal approach for suprasellar and infrasellar lesions is restricted exposure. Microscope and endoscope-assisted procedures have traditionally used an oval-shaped speculum, the distal end of which restricts superior and inferior visualization. To improve visualization and use of the endoscope, shorter specula, with a trapezoidal distal end, were designed. METHODS: The new specula have a working length of 60 mm. The proximal 20-mm segment is oval-shaped to conform to the nostril; the middle 20-mm segment has vertically oriented blades; and the distal 20-mm segment transitions to a trapezoidal orientation, with the distal blades angled 15 degrees upward and outward on the suprasellar speculum, or 15 degrees downward and outward on the infrasellar speculum. Both specula have a 5-degree distal outward flare. The upward-angled trapezoidal 60-mm speculum was compared with 70- and 80-mm oval specula in a transsphenoidal clay model. A pen light was projected from the nasal speculum end to a target 100 mm away using a blade opening width of 16 mm. Line drawings were made to quantify the impact of speculum length on the horizontal angle of exposure. The clinical utility of the trapezoidal specula was also assessed. RESULTS: In the model, the 60-mm upward-angled trapezoidal speculum yielded a surface area illumination of 759 mm, as compared with 579 and 432 mm with the 70-and 80-mm oval specula, an increase in exposure of 31 and 76%, respectively. In the line drawings, the 60-mm speculum provided a horizontal angle of exposure of 30 degrees, as compared with 26 and 23 degrees for the 70- and 80-mm specula, an increase of 17 and 33%, respectively. In patients, provided sufficient mucosa and bone are removed from the posterior nasal cavity, the trapezoidal specula provide an expanded working volume that facilitates endoscopy. CONCLUSION: Short upward- or downward-angled trapezoidal endonasal specula increase parasellar surface area exposure and the horizontal angle of exposure. Initial clinical experience suggests that reducing the speculum length and eliminating the distal curved blades result in greater instrument maneuverability and enhanced visibility for removing parasellar tumors.

Choroid plexus hyperplasia: surgical treatment and immunohistochemical results. Case report.

Diffuse villous hyperplasia of the choroid plexus is a rare but potential source of nonobstructive hydrocephalus. In addition to discussing the authors' staged surgical approach and medical management decisions in a patient with this rare and challenging condition, immunohistochemical studies of the choroid plexus epithelium are presented to examine the pathophysiological factors involved in abnormal cerebrospinal fluid (CSF) production in this disease. The patient, a 15-month-old girl born at 36 weeks' gestation, underwent a bilateral craniotomy with resection of the choroid plexus to treat her villous hyperplasia. Immunohistochemical studies of the resected choroid plexus were conducted for the purpose of examining the carbonic anhydrase II (CAII) enzyme and the aquaporin 1 (AQP1) membrane protein. Results were compared with immunohistochemical studies conducted in a small series of autopsy specimens of normal human choroid plexuses. There was no change in the immunoreactivity of CAII in the patient with villous hyperplasia compared with normal controls, whereas AQP1 immunoreactivity was significantly weaker in the patient compared with normal controls. Postoperatively, the patient's CSF overproduction resolved and her neurological symptoms improved over time. Shunting techniques and presently available pharmaceutical treatments alone do not provide adequate treatment of high-output CSF conditions. Surgical removal of the affected choroid plexus is a feasible and effective treatment. Results of the immunohistochemical studies reported here support the suggestion that the CAII enzyme is retained in villous hyperplasia of the choroid plexus. However, there appears to be decreased expression and perhaps downregulation of AQP1 in villous hyperplasia compared with normal choroid plexus. Future studies may elucidate the significance of these observations.

Contralateral conjugate eye deviation during deep brain stimulation of the subthalamic nucleus.

OBJECT: Deep brain stimulation of the subthalamic nucleus (STN) in patients with Parkinson disease is often very effective for treatment of debilitating motor symptoms. Nevertheless, the small size of the STN and its proximity to axonal projections results in multiple side effects during high-frequency stimulation. Contralateral eye deviation is produced in a small percentage of patients, but the precise mechanism of this side effect is at present poorly understood. METHODS: Contralateral eye deviation was produced by high-frequency stimulation of 22 contact sites in nine patients undergoing deep brain stimulation of the STN. The precise locations of these contacts were calculated and compiled in order to locate the stimulated structure responsible for eye deviation. RESULTS: The mean x, y, and z coordinates associated with contralateral eye deviation were found to be 11.57, 2.03, and 3.83 mm lateral, posterior, and inferior to the anterior commissure-posterior commissure midpoint, respectively. The point described by these coordinates is located within the lateral anterosuperior border of the STN. CONCLUSIONS: Given that stimulation of frontal eye field cortical regions produces similar contralateral conjugate eye deviation, these results are best explained by electrical current spread to nearby frontal eye field axons coursing lateral to the STN within the internal capsule. Thus, placement of the implanted electrode in a more medial, posterior, and inferior position may bring resolution of these symptoms by reducing the amount of current spread to internal capsule ax-

Avoidance of carotid artery injuries in transsphenoidal surgery with the Doppler probe and micro-hook blades.

OBJECTIVE: Internal carotid artery (ICA) injury during sellar dural opening is a potentially catastrophic complication of transsphenoidal surgery. We describe two ICA injuries that occurred early in our endonasal transsphenoidal experience. We then describe our subsequent protocol to prevent this complication in which we use the Doppler probe for carotid localization and micro-hook blades for lateral dural opening. METHODS: All patients undergoing endonasal tumor removal were analyzed since beginning this approach in 1998. Of 631 procedures (585 patients), three patients sustained an ICA injury. RESULTS: In the first 114 procedures (105 patients) in which the Doppler probe was not used and hook blades were used infrequently, two (1.8%) ICA injuries occurred. In both cases, a right nostril approach was used and the left ICA was punctured on dural opening with a straight scalpel; both patients recovered without neurological sequelae. In the subsequent 517 procedures in which the Doppler probe and hook blades were used in all cases, one (0.19%) probable ICA injury occurred during an attempted removal of a cavernous sinus schwannoma, although there was no angiographic evidence of vascular injury. There were no ICA or other intracranial vascular injuries in the last 510 procedures for tumors not solely confined to the cavernous sinus. CONCLUSION: Cavernous carotid localization with the Doppler probe before dural opening and angled hook blades for lateral dural opening can help minimize the risk of ICA injury and are recommended for all transsphenoidal operations. Because of the wider contralateral exposure provided by the endonasal approach, the ICA contralateral to the nostril of approach is at higher risk of injury on dural opening.

Suboptimal sphenoid and sellar exposure: a consistent finding in patients treated with repeat transsphenoidal surgery for residual endocrine-inactive macroadenomas.

OBJECTIVE: In a series of patients with residual endocrine-inactive macroadenomas who underwent repeat surgery, we assess possible reasons for prior subtotal removal, reoperative success, complication rates, and patient impressions. METHODS: All patients were identified who had a prior subtotal removal of an endocrine-inactive macroadenoma and were reoperated on for residual sellar tumor via an endonasal approach. RESULTS: Over 6 years, of 188 consecutive patients with endocrine-inactive adenomas, 30 (16%) had repeat surgery (age, 15-77 yr; median interval between surgeries, 25 mo; median follow-up, 20 mo). Maximal tumor diameter averaged 2.4 +/- 0.9 cm. At reoperation, a suboptimal bony exposure was seen in all 30 patients: at the sphenoid keel, the sella, or both in 97, 93, and 90% of patients, respectively. Cavernous sinus invasion was seen in 16 (53%) patients and a fibrous/rubbery consistency in 12 (40%). Gross total tumor removal was achieved in 17 (57%) patients, including 12 of 14 (86%) with noninvasive tumors and 5 of 16 (31%) with invasive tumors, (P < 0.01). All six fibrous/rubbery but noninvasive tumors were totally removed. Of 16 patients with preoperative visual loss, 15 (94%) improved. Complications included one each of cerebrospinal fluid leak, delayed sinusitis, and new hypothyroidism. In 17 patients with prior sublabial surgery who completed questionnaires, the second (endonasal) surgery was associated with an easier recovery, less pain, and better nasal airflow in 82, 88, and 93%, respectively (P < 0.0001). CONCLUSION: In patients with residual sellar endocrine-inactive adenomas, a suboptimal opening at the sphenoid keel or sella at the first surgery and a high proportion of fibrous/rubbery tumors likely contributed to prior subtotal removal of otherwise accessible tumor. With a wider exposure, most noninvasive tumors can be totally removed, whereas invasive tumors can be effectively debulked. An endonasal reoperation is well tolerated with a low complication rate.