The central nervous system (CNS) is less prone to infection owing to protection from the brain-blood barrier. However, craniotomy destroys this protection and increases the risk of infection in the brain of patients who have undergone craniotomy. CNS infection after craniotomy significantly increases the patient\'s mortality rate and disability. Controlling the occurrence of intracranial infection is very important for post-craniotomy patients. CNS infection after craniotomy is caused by several factors such as preoperative, intraoperative, and post-operative factors. Craniotomy may lead to postsurgical intracranial infection, which is mainly associated with surgery duration, infratentorial (posterior fossa) surgery, cerebrospinal fluid leakage, drainage tube placement, unregulated use of antibiotics, glucocorticoid use, age, diabetes, and other systemic infections. Understanding the risk factors of CNS infection after craniotomy can benefit reducing the incidence of intracranial infectious diseases. This will also provide the necessary guidance and evidence in clinical practice for planning to control intracranial infection in patients with craniotomy.

OBJECTIVE: The nomenclature characterizing posterior fossa (PF) extraventricular (EV) CSF collections in radiological reports can be quite variable, leading to uncertainty about the subsequent clinical course that may result in multiple follow-up imaging studies that may not be needed and occasionally to operative intervention that is not warranted. The important factor is the mass effect of the PF EV CSF collection on adjacent structures, the presence of hydrocephalus, and the likelihood of the CSF collection increasing in size over time.
METHODS: The authors respectively reviewed the imaging database at Children\'s Hospital Los Angeles to identify all radiological reports from 2000 to 2015 indicating the presence of an EV CSF collection in the PF that was characterized as containing an arachnoid cyst, being cystic, or being an abnormal CSF collection.
RESULTS: Of the 332 reports in 65 patients, the PF EV CSF collection was described as an arachnoid cyst or cystic in 306 with 20 different terms being used. In those patients who underwent multiple imaging studies, the PF EV CSF collection was often described differently in each report. Of this group, 47 (72%) patients did not undergo PF surgery. Eighteen (28%) patients did undergo PF surgery, of whom 14 had both hydrocephalus and brainstem displacement, 2 had brainstem displacement but no hydrocephalus, and 2 had neither brainstem displacement nor hydrocephalus and in retrospect did not benefit from PF surgery.
CONCLUSIONS: The terminology in radiology reports describing EV PF CSF collections is variable, is inconsistent, and does not correlate well with clinical management or the need for PF surgery. Significant brainstem displacement and hydrocephalus in the presence of EV PF CSF collection is highly correlated with the need for PF surgery. The incidence of a PF EV CSF collection increasing to become symptomatic becomes more remote the older the patient is at the time of diagnosis as compared with those that occur mainly in infancy. There are true EV CSF cysts in the PF, but the ones that are of consequence are those that exert pressure on the brainstem, obstruct CSF flow, or both. Calling any increased amount of CSF in the PF a \"cyst\" or \"cystic\" can cause uncertainty, leading to one or more subsequent imaging studies or, in rare cases, unwarranted operative intervention.

OBJECTIVE: The rhomboid lip is a neural tissue encountered during cerebellopontine angle surgery, with differing shape and extent among individuals. This study aimed to investigate the variation of rhomboid lips during posterior fossa surgery.
METHODS: In this retrospective study, we examined posterior cranial fossa surgeries performed using a retrosigmoid approach. Rhomboid lips were classified according to thickness, extent, and appearance, with some subjected to histological analysis. T2-weighted magnetic resonance imaging of rhomboid lips was conducted.
RESULTS: Among 304 surgeries, rhomboid lips were observed in 75 patients who underwent schwannoma or meningioma resection, facial spasm-related neurovascular decompression, and other surgeries (37, 2, 32, and 4 patients, respectively). Rhomboid lips were categorized based on apparent thickness: thin membranous type, resembling an arachnoid membrane, and thick parenchymal type. Rhomboid lip extension was classified by position relative to the choroid plexus: nonextension, lateral extension, and jugular foramen (41, 22, and 12 patients, respectively). Veins were observed on the rhomboid lip surface in 37 cases. The rhomboid lip was visible in only 1 case (parenchymal jugular foramen type) on magnetic resonance imaging. Histologically, the rhomboid lip comprised an ependymal cell layer, a glial layer, and connecting tissue. The glial layer thickness determined the rhomboid lip thickness, which was greater in the parenchymal type than in the membrane type. In 42 patients, the rhomboid lip was dissected with no complications observed.
CONCLUSIONS: Morphological classification of the rhomboid lip and understanding of its anatomical details contribute to safe surgical field development for neurosurgeons.

BACKGROUND: Arteriovenous malformation (AVM)-associated aneurysms represent a high-risk feature predisposing them to rupture. Infratentorial AVMs have been shown to have a greater incidence of associated aneurysms, however the existing data is outdated and biased. The aim of our research was to compare the incidence of supratentorial vs infratentorial AVM-associated aneurysms.
METHODS: Patients were identified from our institutional AVM registry, which includes all patients with an intracranial AVM diagnosis since 2000, regardless of treatment. Records were reviewed for clinical details, AVM characteristics, nidus location (supratentorial or infratentorial), and presence of associated aneurysms. Statistical comparisons were made using Fisher\'s exact or Wilcoxon rank sum tests as appropriate. Multivariable logistic regression analysis determined independent predictors of AVM-associated aneurysms. As a secondary analysis, a systematic literature review was performed, where studies documenting the incidence of AVM-associated aneurysms stratified by location were of interest.
RESULTS: From 2000-2024, 706 patients with 720 AVMs were identified, of which 152 (21.1%) were infratentorial. Intracranial hemorrhage was the most common AVM presentation (42.1%). The incidence of associated aneurysms was greater in infratentorial AVMs compared with supratentorial cases (45.4% vs 20.1%; P<0.0001). Multivariable logistic regression demonstrated that infratentorial nidus location was the singular predictor of an associated aneurysm, odds ratio: 2.9 (P<0.0001). Systematic literature review identified eight studies satisfying inclusion criteria. Aggregate analysis indicated infratentorial AVMs were more likely to harbor an associated aneurysm (OR 1.7) and present as ruptured (OR 3.9), P<0.0001.
CONCLUSIONS: In this modern consecutive patient series, infratentorial nidus location was a significant predictor of an associated aneurysm and hemorrhagic presentation.

BACKGROUND: Chiari I malformation (CM-I) is defined as the extension of brain tissue into the spinal cord. This study aimed to refine the methodology for the acquisition of 3-dimensional measurements of the posterior fossa and introduce occipital keel size as a new marker and its impact in patients with CM.
METHODS: In this retrospective study, all patients who underwent Chiari decompression surgery at Montefiore Medical Center from April 2012 to April 2022 were included. Perioperative clinical information was obtained in addition to maximal keel thickness (KT), foramen magnum area, and preoperative and postoperative posterior fossa volumes for each patient and age-matched controls. Volumetric measurements were obtained using artificial intelligence-based semiautomated segmentation.
RESULTS: A total of 107 patients with CM including 37 males, and 70 females were studied with a mean age of 26.56 ± 17.31 compared with 103 controls without CM. The comparison between the CM and the general population groups demonstrated a significantly increased keel size in Chiari patients. Keel size had a significant relationship with dysphagia, paresthesia, and intraoperative blood loss, while posterior volume change had a significant relationship with sex and early symptomatic improvement. The Foramen magnum area was related to tonsillar descent and more prominent in patients with spina bifida.
CONCLUSIONS: The Keel of Goodrich is a new anatomical factor that should be taken into consideration when evaluating preoperative symptoms, and intraoperative complications in patients with CM-I. Volumetric analyses demonstrated that posterior fossa volume change had a significant impact on early symptom improvement in patients with Chiari, as did the choice of operative approach. The routine use of semiautomated segmentation of the posterior fossa may help stratify Chiari patients in the future and should be implemented in routine clinical care.

Despite its broad use in cranial and spinal surgery, navigation support and microscope-based augmented reality (AR) have not yet found their way into posterior fossa surgery in the sitting position. While this position offers surgical benefits, navigation accuracy and thereof the use of navigation itself seems limited. Intraoperative ultrasound (iUS) can be applied at any time during surgery, delivering real-time images that can be used for accuracy verification and navigation updates. Within this study, its applicability in the sitting position was assessed. Data from 15 patients with lesions within the posterior fossa who underwent magnetic resonance imaging (MRI)-based navigation-supported surgery in the sitting position were retrospectively analyzed using the standard reference array and new rigid image-based MRI-iUS co-registration. The navigation accuracy was evaluated based on the spatial overlap of the outlined lesions and the distance between the corresponding landmarks in both data sets, respectively. Image-based co-registration significantly improved (p < 0.001) the spatial overlap of the outlined lesion (0.42 ± 0.30 vs. 0.65 ± 0.23) and significantly reduced (p < 0.001) the distance between the corresponding landmarks (8.69 ± 6.23 mm vs. 3.19 ± 2.73 mm), allowing for the sufficient use of navigation and AR support. Navigated iUS can therefore serve as an easy-to-use tool to enable navigation support for posterior fossa surgery in the sitting position.

OBJECTIVE: The endoscopic transorbital approach (ETOA) has been demonstrated to be a feasible ventral route to the petrous apex. Yet, it has been pointed to as a deep and narrow corridor for anterior petrosectomy; particularly, medialization of the instruments can become an issue when targeting the petroclival area. To overcome this limitation, an ETOA with orbital rim removal (ETOA-OR) has been suggested, but not de facto compared, with a transorbital approach without removal of the rim. This addition could augment the surgical exposure and freedom of movement when accessing the petrous apex area.
METHODS: Five human cadaveric heads (10 sides) were dissected. First, anterior petrosectomy was performed via a conventional ETOA (without orbital rim removal). Second, en bloc removal of the orbital rim was performed, with enlargement of the orbital craniectomy and, subsequently, further drilling of the medial petrous apex. Qualitative and quantitative comparisons are provided. An illustrative surgical case is also shown.
RESULTS: The transorbital route allowed the authors to perform an anterior petrosectomy in all specimens. The landmarks of bone removal are superposed onto those in the transcranial route. The ETOA-OR increased the volume of craniectomy (from 4.0 mL to 5.5 mL), the lateromedial angulation, and superoinferior angulation of the instruments within the petrous area. Thus, this approach improved the exposure of the medial petroclival area, allowing for an augmented petrosectomy (from 1.4 mL to 2.0 mL, 39.5% increase) and for increased maneuverability, both in the petrous area (from 44.1 cm2 to 76.5 cm2, 73.3% increase) and in the posterior fossa (from 20.2 cm2 to 52.0 cm2, 158% increase). The ETOA-OR was also pragmatically applied to treat a recurrent petroclival meningioma. Complete removal was achieved, the abducens nerve palsy improved, and the trigeminal neuralgia decreased in severity, yet still required medication.
CONCLUSIONS: The authors provide the first formal anatomical comparison between the transorbital approach with preservation of the orbital rim and a transorbital approach with removal of the rim to access the petrous apex. In addition, an illustrative case is used as a proof of concept and feasibility. According to the authors\' data, the ETOA-OR significantly improves surgical exposure and the surgeon\'s comfort in this deep region. The bony defect can be reconstructed to avoid cosmetic deformities, maintaining the minimally disruptive concept of transorbital surgery.

Cerebellar liponeurocytoma is a rare WHO grade II glioneuronal tumor, characterized by a benign course and a more favorable prognosis. In this paper, we report a 52-year-old man, hospitalized in emergency because of clinical signs of increased intracranial pressure, and gait disturbances. The MRI revealed a lateral well shaped solid lesion within the left cerebellar hemisphere, having a low signal intensity compared to the cerebrospinal fluid, and causing a triventicular hydrocephalus and tonsillar herniation. The patient underwent a direct approach of the tumor through a left suboccipital craniectomy. Total removal of the lesion was achieved, and the histological diagnosis was cerebellar liponeurocytoma. The tumor cell proliferation index was < 6 %, therefore, radiotherapy and chemotherapy were not implemented after surgery. After 5 years of close follow-up there were no clinical or radiological signs of recurrence. Our objective in reporting another case of this unusual tumor is to discuss clinical profile, radiologic and histologic features as well as treatment and prognosis of this rare posterior fossa tumor.

UNASSIGNED: Traumatic brain injuries involving the posterior fossa are rare and case reports indicate they often result in severe outcomes. We seek to describe characteristics and outcomes of traumatic posterior fossa injuries.
UNASSIGNED: We performed a planned secondary analysis of all patients with posterior fossa injuries enrolled in the NEXUS head computed tomography (CT) validation study dataset. The dataset includes prospectively collected data on all patients undergoing non-contrast cranial CT following blunt traumatic head injury from April 2006 to December 2015, at four emergency departments comprising community and university sites, as well as urban, suburban and rural settings in California (Antelope Valley Hospital, San Francisco General Hospital, UCLA Ronald Reagan Medical Center, UCSF Fresno Community Regional Medical Center). We classified each patient into one of three injury patterns: Type I-notable traumatic injuries primarily above the tentorium, with minimal posterior fossa involvement; Type II-notable traumatic injuries both above and within the posterior fossa; and Type III-notable traumatic injuries primarily within the posterior fossa. We extracted demographic data for each patient as well as physician assessments of the NEXUS head CT and Canadian Head CT rule clinical criteria, mechanisms of injury, patient outcomes, and the location and types of intracranial injuries sustained.
UNASSIGNED: Of 11,770 patients in the database, 184 (1.6%) had posterior fossa injuries on CT imaging. Mean age was 55.4 years (standard deviation 22.5 years, range 2-96 years); 131 (71.2%) were males. We identified 63 patients with Type I injuries, 87 with Type II injuries, and 34 Type III injuries. The most common mechanisms of injury were falls (41%), pedestrian vs automobile (15%), and motor vehicle collisions (13%). On presentation most patients had altered mental status (72%), abnormal behavior (53%), or a neurologic deficit (55%). The majority of individuals, 151 (82%), had clinically important injuries and 111 (60%) required neurosurgical intervention. The dispositions for the subjects included 52 deaths (28%), 49 (27%) patients discharged home, and 48 (26%) discharged to rehabilitation facilities. When compared to individuals with Type I and Type II injuries, patients with Type III injuries had lower mortality (6% vs 30% and 35%) and higher percentage of patients discharged home (60% vs 19% and 21%).
UNASSIGNED: Patients with Type I and II injury patterns (those that involve both the posterior fossa and supratentorium) experienced high mortality and disability. Patients with Type III injuries (isolated posterior fossa) had a better prognosis.
UNASSIGNED: None.

BACKGROUND: Neuronavigation has become an essential system for brain tumor resections. It is sometimes difficult to obtain accurate registration of the neuronavigation with the patient in the prone position. Bony surface-matching registration should be more precise than skin surface-matching registration; however, it is difficult to establish bony registration with limited exposed bone. We created a new bony surface-matching method to a sectioned 3-dimensional (3D) virtual skull in a neuronavigation system and registered with a sectioned 3D skull. In this study, the bony surface-matching with sectioned 3D registration is applied to provide precise registration for brain tumor resection in the prone position.
METHODS: From May 2023 to April 2024, 17 patients who underwent brain tumor resection in the prone position were enrolled. The navigation system StealthStation S8 (Medtronic, Dublin, Ireland) was used. Bony surface-matching registration with a whole 3D skull in a neuronavigation system was performed. Next, a sectioned 3D skull was made according to the surgical location to compare with the whole 3D skull registration. A phantom model was also used to validate the whole and sectioned 3D skull registration.
RESULTS: Whole 3D skull registration was successful for only 2 patients (11.8%). However, sectioned 3D skull registration was successful for 16 patients (94.1%). The examinations with a phantom skull model also showed superiority of sectioned 3D skull registration to whole 3D skull registration.
CONCLUSIONS: Sectioned 3D skull registration was superior to whole 3D skull registration. The sectioned 3D skull method could provide accurate registration with limited exposed bone.