How I do it: safe resection of a complex type 3 foramen magnum meningioma with dorsal displacement of the neurovascular bundle.

BACKGROUND: We describe techniques for safe resection of a Type 3 foramen magnum meningioma with dorsal displacement of the accessory nerve rootlets and vertebral artery which limits ventral access to the tumor. METHOD: Partial sectioning of the accessory nerve rootlets may help create larger working space. Topical lidocaine placement on the rootlets of the spinal accessory nerve may mitigate trapezius muscle contraction and facilitates further progress throughout tumor resection. CONCLUSION: Creating safe working corridors between the lower cranial nerves through mobilization or partial sectioning of rootlets in the case of CN XI facilitates tumor resection through a far lateral approach.

A Prevalence Anatomic-Imaging Study of the Posterior Inferior Cerebellar Artery's Origin.

Background and Objectives: Typically, the vertebral arteries (VAs) enter the posterior fossa through dural rings and further unite, forming the basilar artery. The posterior inferior cerebellar artery (PICA) is usually a branch of the V4 segment of the VA (intradural origin). It may also leave the V3 suboccipital segment of the VA (extradural origin). The transdural origin of the PICA within the VA's dural ring has been consistently overlooked. A study was designed to determine the topographical patterns of the PICA's origin. Materials and Methods: Determinations were performed in a retrospective sample of 225 computed tomography angiograms. Four types of PICA origin were documented: type 0, absent PICA; type 1, the extradural origin of the PICA from the V3 segment of the VA; type 2, the transdural origin of the PICA within the dural ring; and type 3, the intradural origin of the PICA from the V4 segment of the VA. The bilateral symmetry of types was also investigated. Results: Out of 450 VAs, type 0 (absent PICA) was found in 36%, type 1 (extradural) in 0.44%, type 2 (transdural) in 5.56%, and typical type 3 in just 58%. In types 1 and 2, the PICA entered the posterior fossa through the dural ring and the marginal sinus. In the overall group (N = 225), the type combinations 1_1, 1_2 and 1_3 were not found. Bilaterally absent PICAs occurred in 18.67%. The bilateral combinations 0_1/0_2/0_3/2_2/2_3/3_3 were found, respectively, in 0.89%/3.11%/30.67%/1.78%/4.44%/40.44%. Four of the seventy-eight PICAs opposite to an absent one, three intradural and one transdural, were true bihemispheric PICAs. Conclusions: The PICAs with extradural or transdural origins are facultative contents of the dural ring and are at risk during neurosurgical approaches in the foramen magnum. Rare bihemispheric PICAs could originate either intradurally or within the dural ring.

Effect of the Basilar Invagination (Type B) on Cervical Spine: A Case-control Study with MRI.

OBJECTIVE: To evaluate the effect of the basilar invagination (BI) type B on cervical spine. METHODS: The research protocol used head magnetic resonance imaging (MRI) exams from 41 participants with BI type B and 158 controls. The criterion for BI was the distance of the odontoid apex to Chamberlain's line (DOCL) equal to or greater than 7 mm. The clivus length (CLI), clivus canal angle (CCA), Welcker's basal angle (WBA), Boogaard's angle (BOA), upper cervical lordosis angle (UCL), and total cervical lordosis angle (CL) were evaluated. The descriptive analysis, group comparisons, and correlations between skull base and cervical spine parameters were performed at the 95% CI. RESULTS: Participants with BI type B showed shorter clivus length (CLI: 25.7 ± 7.3 mm); greater angulation of the skull base (WBA: 126.5 ± 10.4); greater inclination foramen magnum (BOA: 151.5 ± 14.5); decrease in the value of the CCA (131.6 ± 15); and greater angulations of UCL (17.9 ± 13.8) and CL (29.7 ± 19.9) in comparison to the control group (P < 0.05). Clivus length and CCA correlated inversely with UCL and CL, while BOA correlated directly with UCL and CL. The WBA did not correlate with CL (P < 0.05). CONCLUSIONS: The deformation of skull base in the BI of type B caused, on average, a hyperlordosis of almost 30° in the C2-C6 segment. This change was approximately 17° in the C2-C4, with the clivus hypoplasia being a risk factor for cervical hyperlordosis.

Comprehensive comparative study of Chiari-like malformation in veterinary and human medicine.

This review aims to enrich our understanding of Chiari-like malformation (CLM) by combining human and veterinary insights, and providing a detailed cross-species overview. CLM is a developmental abnormality characterised by caudal displacement of the hindbrain into the foramen magnum due to an entire brain parenchymal shift caused by insufficient skull volume. This malformation leads to a progressive obstruction at the craniocervical junction, which disrupts the normal cerebrospinal fluid flow, leading to secondary syringomyelia. The clinical signs of CLM and syringomyelia include phantom scratching, head tilt, head tremor, ataxia, tetraparesis, pain, muscle atrophy, and scoliosis or torticollis. Magnetic resonance imaging remains the gold standard for diagnosing CLM, since it allows the visualisation of abnormal findings such as the caudal cerebellar herniation, caudal cerebellar compression from occipital dysplasia, and attenuated cerebrospinal fluid cisternae. Although various medical and surgical interventions, including foramen magnum decompression, can provide temporary symptomatic/clinical sign relief, current literature shows a lack of sustained long-term efficacy. Therefore, additional research is needed to evaluate the long-term effects of existing treatment strategies and to compare different techniques utilised in conjunction with foramen magnum decompression.

Preoperative predictors of foramen magnum decompression with dural splitting for amelioration of syringomyelia associated with Chiari type 1 malformation.

OBJECTIVE: Among several procedures for syringomyelia associated with Chiari type 1 malformation (CM-1), foramen magnum decompression (FMD) with dural splitting is one of the treatment choices with low complication rates. However, some meta-analyses have suggested that FMD with dural splitting may be inferior to FMD with duraplasty based on clinical outcomes; therefore, a predictor of a good surgical outcome with dural splitting is essential. This study aimed to clarify the preoperative parameters for good outcomes in patients with FMD with dural splitting, including the volumetric perspective. METHODS: We reviewed the cases of patients diagnosed with CM-1 and syringomyelia who underwent FMD with dural splitting at our institution. We included patients who underwent magnetic resonance imaging (MRI) from 6 months to 1 year after surgery, and measured radiological parameters using preoperative computed tomography and preoperative/follow-up MRI. RESULTS: Thirty-one patients were enrolled. Among all radiological parameters, the volume of the herniated tonsils (Vtonsil) and the difference between the expected volume-increment and Vtonsil (Vincr-Vtonsil) in improved groups were significantly smaller than those in non-improved groups. To predict the improvement of the syrinx, Vincr-Vtonsil of 0.77 mL was the optimal cutoff value, and yielded 100% sensitivity and 48.0% specificity. CONCLUSIONS: Vtonsil and Vincr-Vtonsil, which are novel predictors based on the volumetric perspective, might be the optimal predictors for improvement of the syrinx associated with CM-1 by 1 year after surgery.

Geometric morphometric analysis of the brainstem and cerebellum in Chiari I malformation.

Background: Chiari I malformation (CMI) is characterized by inferior descent of the cerebellar tonsils through the foramen magnum and is associated with headache and neck pain. Many morphometric research efforts have aimed to describe CMI anatomy in the midsagittal plane using classical measurement techniques such as linear dimensions and angles. These methods are less frequently applied to parasagittal features and may fall short in quantifying more intricate anatomy with fewer distinct homologous landmarks. Methods: Landmark-based geometric morphometric techniques were used to asses CMI morphology in five anatomical planes of interest. Results: Significant shape differences between CMI and age/sex-matched controls were found in the midsagittal (Pseudo-F = 5.4841, p = 0.001) and axial planes through the rostral medulla (Pseudo-F = 7.6319, p = 0.001). In addition to tonsillar descent, CMI principal component 1 (PC1) scores in the midsagittal protocol were associated with marked anterior concavity of the brainstem and generalized verticality of the cerebellum with anterior rotation of its anterior lobe. In the axial medulla/cerebellum protocol, CMI PC1 scores were associated with greater anterior-posterior (A-P) dimension with loss of medial-lateral (M-L) dimension. Discussion: These results suggest that CMI is associated with greater curvature of the brainstem and spinal cord, which may perturb normal neural activities and disrupt cerebrospinal fluid movements. Previous reports on the A-P diameter of the posterior fossa in CMI have conflicted; our findings of greater A-P cerebellar dimensionality with concomitant loss of width alludes to the possibility that more caudal aspects of the posterior cranial fossa are more bowl-like (homogenous in axial dimensions) and less trough-like or elongated in the M-L direction.

Management and outcomes of foramen magnum stenosis in children with achondroplasia at a single center over 15 years.

OBJECTIVE: Achondroplasia is associated with foramen magnum stenosis (FMS), which can lead to sudden unexpected death in infants. There is no wide consensus regarding the best management of FMS. This study aimed to analyze the prevalence of FMS in a cohort of children with achondroplasia and to evaluate screening and neurosurgical interventions of FMS regarding its effects and complications. METHODS: The authors conducted a retrospective cohort study including all children with achondroplasia assessed or treated at Karolinska University Hospital between September 2005 and June 2020. The severity of FMS was graded using the MRI Achondroplasia Foramen Magnum Score (AFMS). The AFMS was correlated with neurological examinations and polysomnography (PSG) results. RESULTS: Severe FMS (AFMS 3-4) was present in 35% of the 51 children included in the study. As many as 65% of the children in the cohort underwent foramen magnum decompression (FMD). Neurological examination had a high specificity (94%) but a low sensitivity (28%) for severe FMS. Signs of central apnea on PSG did not correlate with severity of FMS (p = 0.735). Surgery improved FMS (p < 0.001) with a nonsignificant trend of decreased central apnea (p = 0.070), but carried a 9% risk of severe surgery- and anesthesia-related complications. CONCLUSIONS: This study confirmed previous reports that severe FMS is common in children with achondroplasia, that neurological symptoms may be absent even in severe FMS, and that FMD improves FMS and may improve central apnea. The finding that neurological examination had a low sensitivity for severe FMS supports the recommendation that all children with achondroplasia should undergo early MRI.

Communicating hydrocephalus after resection of a meningioma ventral to the foramen magnum.

Background: Tumors in or near the foramen magnum may cause communicating or non-communicating hydrocephalus (HC), depending on their size and location. Here, an 81-year-old female developed communicating HC following the resection of a meningioma ventral to the foramen magnum. Case Description: An 81-year-old female presented with numbness in the left neck and left hemiparesis. The magnetic resonance revealed an 18-mm tumor ventral to the foramen magnum that significantly enlarged over the past 6 months. She underwent total tumor resection but then presented with progressive HC both clinically (i.e., instability of gait with confusion) and radiographically (computed tomography). Following placement of a lumboperitoneal (LP) shunt, symptoms markedly improved. Further, the cerebrospinal fluid (CSF) analysis showed elevated cell counts and protein concentrations, indicating likely "leakage" of intratumoral contents postoperatively contributing to the progressive HC. Conclusion: Patients presenting with acute meningiomas ventral to the foramen magnum may develop postoperative communicating HC attributed to tumor-related CSF leakage of necrotic intratumoral components that can be successfully treated with a LP shunt.

SIADH as a Rare Complication of Foramen Magnum Stenosis in an Infant With Achondroplasia.

Achondroplasia is the most common skeletal dysplasia and is associated with serious complications such as foramen magnum stenosis (FMS). This case report describes an infant with achondroplasia who presented with a syndrome of inappropriate antidiuretic hormone secretion (SIADH), secondary to significant FMS and myelocompression. A 2-month-old boy with prenatally diagnosed achondroplasia was referred due to disordered breathing and altered consciousness. On admission, apathy, hypotonus, and hypothermia with typical features of achondroplasia were noticed. Laboratory investigations revealed severe hyponatremia and hypochloridaemia with normal glucose and urea levels. The diagnosis of SIADH was made based on low serum osmolality in the presence of high urine osmolality, along with an elevated copeptin level. An emergency computerized tomography showed a high-grade stenosis at the cranio-cervical junction; subsequent magnetic resonance imaging demonstrated myelocompression. The patient underwent decompression surgery the next day; serum osmolality increased after the operation. Spontaneous breathing after extubation was sufficient whereas tetraplegia persisted despite intensive physiotherapy. Clinicians should be aware of SIADH as a presenting sign of FMS in children with achondroplasia. Further discussion is warranted regarding improving parental education and timing of screening recommendations.

Sleep-disordered breathing in children with Chiari type I malformation.

OBJECTIVE: The objective was to identify clinical and radiological factors associated with sleep-disordered breathing (SDB) in children with Chiari type I malformation (CIM) and to evaluate the efficacy of foramen magnum decompression (FMD) in resolving SDB. METHODS: A retrospective chart review was conducted for all children evaluated for CIM at a single institution from 2002 to 2022, identifying all children who had undergone nocturnal polysomnography (PSG). Apnea-hypopnea index (AHI) score, sleep apnea type (obstructive, central, mixed, and unspecified), clinical manifestations, and radiological measurements were recorded. SDB was considered present when officially diagnosed in the PSG report. Logistic regression was performed to identify factors correlating with the presence of SDB. For children with SDB who underwent FMD, the Wilcoxon signed-rank test was used to assess AHI improvement. RESULTS: Of the 997 children referred for CIM, 310 completed PSG. SDB was diagnosed in 147 patients (overall prevalence 14.7%, 95% CI 12.7%-17.1%; prevalence among children with PSG 47.4%, 95% CI 41.9%-53%). Specific SDB diagnosis consisted of 33% of patients with central sleep apnea, 27% with obstructive sleep apnea, 9% mixed, and 31% unspecified. Lower cranial nerve (CN) dysfunction (OR 3.891, p = 0.009), tonsillar position (OR 1.049, p = 0.017), Chiari type 1.5 malformation (OR 1.862, p = 0.044), and BMI (OR 1.039, p = 0.036) were significantly associated with presence of SDB. Of the 310 patients who underwent PSG, 47 were originally categorized as asymptomatic: 27 (57%) of these asymptomatic patients were diagnosed with SDB on PSG. Of children diagnosed with SDB, 34 completed PSG before and after FMD. Median AHI score decreased from 6.5 preoperatively to 1.8 postoperatively, with a median (IQR) difference of -2.3 (-11.9 to 0.1) (p = 0.001). Twelve (35%) had resolution of SDB. CONCLUSIONS: The authors' findings suggest that the prevalence of SDB in children with CIM is high (15%-47%). Furthermore, lower CN dysfunction, Chiari type 1.5, lower tonsillar position, and higher BMI may be risk factors. Notably, SDB can be present even in the absence of clinical symptoms. This study also demonstrates that surgical intervention has the potential to reduce the severity of SDB. These results could help clinicians identify CIM patients at risk for SDB and those who may benefit from surgical decompression.

Soft Tissue Dissection in the Transcondylar Approach: A Modified Layered Technique to Maximize Lateral Access.

Objective While the transcondylar approach is technically challenging, it provides generous ventral and caudal exposure to the craniovertebral junction. This approach requires navigation around multiple eloquent neurovascular structures including the lower cranial nerves, vertebral artery and its branches, and the brainstem. Superficial exposure, including incision location and muscle dissection, can dramatically affect the surgical angle and maneuverability at depth. Methods We demonstrate the transcondylar approach in a step-by-step fashion in a formalin-embalmed, latex-injected cadaver head. Dissection within each layer of the suboccipital muscles was performed. A small cohort with an illustrative case is also included herein. Results The sternocleidomastoid (SCM) muscle was retracted anteriorly; the splenium capitis, semispinalis capitis, and longissimus capitis muscles were disconnected from the superior nuchal line and reflected inferomedially. The suboccipital muscle group was fully exposed. The superior and inferior oblique muscles were disconnected from the transverse process of C1. The superior oblique and the rectus capitis posterior major muscles were then dissected off the inferior nuchal line, and the suboccipital muscle group was retracted inferomedially en bloc . The greater auricular nerve was retracted laterally with the SCM, and the greater occipital nerve was retracted inferomedially with the suboccipital muscle group. Conclusion This technique avoids the obstructive muscle bulk that results from a myocutaneous approach while maximizing deep exposure. Understanding the detailed muscular anatomical relationship with the insertion location and suboccipital nerves is key to complete and safe extracranial dissection. Diligent dissection helps minimize postoperative pain and muscle spasm while optimizing the closure technique.

[Accessory nerve meningioma. A case report and literature review]. / Meningioma obolochek dobavochnogo nerva. Klinicheskii sluchai i obzor literatury.

Meningiomas arising from accessory nerve sheath without dural attachment are rare. To date, only 5 cases are described in the literature. A 53-year-old male presented with long history of occipital pain and headaches. Magnetic resonance imaging revealed a small intradural extramedullary contrast enhanced tumor at the level of foramen magnum. The patient underwent microsurgical resection through minimally invasive midline suboccipital approach. According to intraoperative findings, cystic tumor arose from the left accessory nerve without dural attachment. Gross total resection was achieved without damage to the nerve. Histological analysis revealed angiomatous meningioma. Postoperative period was uneventful without new neurological symptoms. Meningiomas can rarely arise from accessory nerve sheath and mimic schwannoma. These tumors may be totally resected without damage to accessory nerve using minimally invasive surgical approaches.

An inexpensive foramen magnum decompression training tool: Feasibility and validation study.

Foramen magnum decompression (FMD) is a standard neurosurgical procedure, typically utilized to treat Chiari malformation. The aim of this educational project was to develop and validate a low-cost FMD simulation training model. Mold-based methods were used to develop a prototype. Feasibility was tested during an FMD training session for 17 neurosurgery trainees. Face and content validity were assessed through a Likert Scale. The perceived training benefit was determined using the Physician Performance Diagnostic Inventory Scale (PPDIS). A total of 87.5% successfully removed the C1 arch, 81.3% successfully performed an FMD, and 68.8% avoided injury to the underlying structures. The model scored highly for visual and tactile realism. The median confidence rating on PPDIS significantly improved from early learner to competent. We demonstrate feasibility, content, and face validity. Furthermore, this is a low-cost, portable model that can be easily replicated and used for simulation training.

Calcifying pseudoneoplasms of the neuraxis (CAPNON) in foramen magnum (cervicomedullary junction) region: a case report and review of the literature.

BACKGROUND AND IMPORTANCE: Calcifying pseudoneoplasms of the neuraxis (CAPNON) is an extremely rare tumor, with nearly 150 cases have been reported in the literature. We present a case of CAPNON at foramen magnum (cervicomedullary junction). We also discuss the histological and radiological features of this rare pathology. CLINICAL PRESENTATION: A 35-year-old male patient presented to our center complaining of neck pain for the last 6 months and for the last 3 months has had headaches associated with nausea, blurred vision and papilledema. The patient's magnetic resonance imaging showed the presence of right craniocervical junction intra-dural extramedullary tumor. Neuro examination showed no neurological deficits. He underwent midline suboccipital craniotomy with C1 laminectomy. The mass was completely resected, and histopathology confirmed it to be a CAPNON. CONCLUSION: We presented a new case of CAPNON at cervicomedullary junction. The tumor was radically resected, without any complications. Resection of this kind of tumor is curative, and the need for post-operative chemo or radiotherapy is unnecessary, which depends on the outcome of future research and the long-term follow ups.

Sleep-Disordered Breathing in an Infant With Achondroplasia and Foramen Magnum Stenosis.

Sleep-disordered breathing (SDB) is a frequently recognized comorbidity in infants and children with achondroplasia due to alterations in craniofacial and upper airway anatomy. Foramen magnum stenosis and cervicomedullary compression can be associated with SDB in this population, requiring prompt evaluation by multidisciplinary teams. Untreated SDB is associated with adverse cardiovascular, metabolic, and behavioral effects in children, necessitating early screening and treatment of underlying causes. Cervicomedullary compression is also associated with increased mortality and sudden infant death in infants with achondroplasia. Management of SDB in children with achondroplasia may involve a combination of neurosurgical intervention, adenotonsillectomy, and/or continuous positive airway pressure (CPAP). We recognize a need for increased physician awareness of the recommended screening guidelines to optimize health outcomes for children with achondroplasia. In this report, we describe a case of a five-month-old infant with achondroplasia and severe SDB diagnosed by polysomnography and was found to have moderate-to-severe foramen magnum stenosis identified by MRI. Subsequently, this infant underwent foramen magnum decompression, which improved the severe SDB and was followed up for five years. Our case illustrates the importance of early screening in infants with achondroplasia for SDB to prevent further sequelae.

Machine learning for enhanced prognostication: predicting 30-day outcomes following posterior fossa decompression surgery for Chiari malformation type I in a pediatric cohort.

OBJECTIVE: Chiari malformation type I (CM-I) is a congenital disorder occurring in 0.1% of the population. In symptomatic cases, surgery with posterior fossa decompression (PFD) is the treatment of choice. Surgery is, however, associated with peri- and postoperative complications that may require readmission or renewed surgical intervention. Given the associated financial costs and the impact on patients' well-being, there is a need for predictive tools that can assess the likelihood of such adverse events. The aim of this study was therefore to leverage machine learning algorithms to develop a predictive model for 30-day readmissions and reoperations after PFD in pediatric patients with CM-I. METHODS: This was a retrospective study based on data from the National Surgical Quality Improvement Program-Pediatric database. Eligible patients were those undergoing PFD (Current Procedural Terminology code 61343) for CM-I between 2012 and 2021. Patients undergoing surgery for tumors or vascular lesions were excluded. Unplanned 30-day readmission and unplanned 30-day reoperation were the main study outcomes. Additional outcome data considered included the length of hospital stay, 30-day complications, discharge disposition, and 30-day mortality. Training and testing samples were randomly generated (80:20) to study the 30-day readmission and reoperation using logistic regression, decision tree, random forest (RF), K-nearest neighbors, and Gaussian naive Bayes algorithms. RESULTS: A total of 7106 pediatric patients undergoing PFD were included. The median age was 9.2 years (IQR 4.7, 14.2 years). Most of the patients were female (56%). The 30-day readmission and reoperation rates were 7.5% and 3.4%, respectively. Headaches (32%) and wound-related complications (30%) were the most common reasons for 30-day readmission, while wound revisions and evacuation of fluid or blood (62%), followed by CSF diversion-related procedures (28%), were the most common reasons for 30-day reoperation. RF classifiers had the highest predictive accuracy for both 30-day readmissions (area under the curve [AUC] 0.960) and reoperations (AUC 0.990) compared with the other models. On feature importance analysis, sex, developmental delay, ethnicity, respiratory disease, premature birth, hydrocephalus, and congenital/genetic anomaly were some of the variables contributing the most to both RF models. CONCLUSIONS: Using a large-scale nationwide dataset, machine learning models for the prediction of both 30-day readmissions and reoperations were developed and achieved high accuracy. This highlights the utility of machine learning in risk stratification and surgical decision-making for pediatric CM-I.

A regulatory variant impacting TBX1 expression contributes to basicranial morphology in Homo sapiens.

Changes in gene regulatory elements play critical roles in human phenotypic divergence. However, identifying the base-pair changes responsible for the distinctive morphology of Homo sapiens remains challenging. Here, we report a noncoding single-nucleotide polymorphism (SNP), rs41298798, as a potential causal variant contributing to the morphology of the skull base and vertebral structures found in Homo sapiens. Screening for differentially regulated genes between Homo sapiens and extinct relatives revealed 13 candidate genes associated with basicranial development, with TBX1, implicated in DiGeorge syndrome, playing a pivotal role. Epigenetic markers and in silico analyses prioritized rs41298798 within a TBX1 intron for functional validation. CRISPR editing revealed that the 41-base-pair region surrounding rs41298798 modulates gene expression at 22q11.21. The derived allele of rs41298798 acts as an allele-specific enhancer mediated by E2F1, resulting in increased TBX1 expression levels compared to the ancestral allele. Tbx1-knockout mice exhibited skull base and vertebral abnormalities similar to those seen in DiGeorge syndrome. Phenotypic differences associated with TBX1 deficiency are observed between Homo sapiens and Neanderthals (Homo neanderthalensis). In conclusion, the regulatory divergence of TBX1 contributes to the formation of skull base and vertebral structures found in Homo sapiens.

Immediate postoperative resolution of syrinx post-C1/C2 fixation in an operated case of foramen magnum decompression for Chiari malformation: Is Goel's procedure a rescue surgery or a gold standard?

Chiari malformation (CM) is a common neurological disorder with foramen magnum decompression (FMD) as a commonly accepted treatment. The authors present a case of CM-1 wherein there was no radiological instability preoperatively and FMD was done as a treatment, after which the patient improved transiently only to deteriorate further. Atlantoaxial fixation was done as a second-stage procedure, after which the patient improved clinically and radiologically. The knowledge of this case and surgical entity should be borne in mind before the formulation of a treatment plan. It is important that the solution is to identify and treat the underlying pathology rather than to decompress and directly manipulate the tonsils.

Novel classification of foramen magnum meningiomas predicted by topographic position relative to neurovascular bundle.

PURPOSE: Proximity to critical neurovascular structures can create significant obstacles during surgical resection of foramen magnum meningiomas (FMMs) to the detriment of treatment outcomes. We propose a new classification that defines the tumor's relationship to neurovascular structures and assess correlation with postoperative outcomes. METHODS: In this retrospective review, 41 consecutive patients underwent primary resection of FMMs through a far lateral approach. Groups defined based on tumor-neurovascular bundle configuration included Type 1, bundle ventral to tumor; Type 2a-c, bundle superior, inferior, or splayed, respectively; Type 3, bundle dorsal; and Type 4, nerves and/or vertebral artery encased by tumor. RESULTS: The 41 patients (range 29-81 years old) had maximal tumor diameter averaging 30.1 mm (range 12.7-56 mm). Preoperatively, 17 (41%) patients had cranial nerve (CN) dysfunction, 12 (29%) had motor weakness and/or myelopathy, and 9 (22%) had sensory deficits. Tumor type was relevant to surgical outcomes: specifically, Type 4 demonstrated lower rates of gross total resection (65%) and worse immediate postoperative CN outcomes. Long-term findings showed Types 2, 3, and 4 demonstrated higher rates of permanent cranial neuropathy. Although patients with Type 4 tumors had overall higher ICU and hospital length of stay, there was no difference in tumor configuration and rates of postoperative complications or 30-day readmission. CONCLUSION: The four main types of FMMs in this proposed classification reflected a gradual increase in surgical difficulty and worse outcomes. Further studies are warranted in larger cohorts to confirm its reliability in predicting postoperative outcomes and possibly directing management decisions.

Promising horizons in achondroplasia along with the development of new drugs.

Achondroplasia (ACH) is a representative skeletal disorder characterized by rhizomelic shortened limbs and short stature. ACH is classified as belonging to the fibroblast growth factor receptor 3 (FGFR3) group. The downstream signal transduction of FGFR3 consists of STAT1 and RAS/RAF/MEK/ERK pathways. The mutant FGFR3 found in ACH is continuously phosphorylated and activates downstream signals, resulting in abnormal proliferation and differentiation of chondrocytes in the growth plate and cranial base synchondrosis. A patient registry has been developed and has contributed to revealing the natural history of ACH patients. Concerning the short stature, the adult height of ACH patients ranges between 126.7-135.2 cm for men and 119.9-125.5 cm for women in many countries. Along with severe short stature, foramen magnum stenosis and spinal canal stenosis are major complications: the former leads to sleep apnea, breathing disorders, myelopathy, hydrocephalus, and sudden death, and the latter causes pain in the extremities, numbness, muscle weakness, movement disorders, intermittent claudication, and bladder-rectal disorders. Growth hormone treatment is available for ACH only in Japan. However, the effect of the treatment on adult height is not satisfactory. Recently, the neutral endopeptidase-resistant CNP analogue vosoritide has been approved as a new drug for ACH. Additionally in development are a tyrosine kinase inhibitor, a soluble FGFR3, an antibody against FGFR3, meclizine, and the FGF2-aptamer. New drugs will bring a brighter future for patients with ACH.