Ciliopathies and the Kidney: A Review.

Primary cilia are specialized sensory organelles that protrude from the apical surface of most cell types. During the past 2 decades, they have been found to play important roles in tissue development and signal transduction, with mutations in ciliary-associated proteins resulting in a group of diseases collectively known as ciliopathies. Many of these mutations manifest as renal ciliopathies, characterized by kidney dysfunction resulting from aberrant cilia or ciliary functions. This group of overlapping and genetically heterogeneous diseases includes polycystic kidney disease, nephronophthisis, and Bardet-Biedl syndrome as the main focus of this review. Renal ciliopathies are characterized by the presence of kidney cysts that develop due to uncontrolled epithelial cell proliferation, growth, and polarity, downstream of dysregulated ciliary-dependent signaling. Due to cystic-associated kidney injury and systemic inflammation, cases result in kidney failure requiring dialysis and transplantation. Of the handful of pharmacologic treatments available, none are curative. It is important to determine the molecular mechanisms that underlie the involvement of the primary cilium in cyst initiation, expansion, and progression for the development of novel and efficacious treatments. This review updates research progress in defining key genes and molecules central to ciliogenesis and renal ciliopathies.

The varied semiology of seizures in the context of small anterior temporal encephaloceles.

Small encephaloceles of the anterior temporal pole have been increasingly recognised as an underlying epileptogenic substrate in patients with medically refractory epilepsy. The current report aims to expand on the current knowledge by emphasising that seizure semiology in such patients can vary significantly. Patients were selected from an epilepsy surgery database between 2012 and 2017. Of the 143 patients who underwent epilepsy surgery, six patients had a temporal encephalocele. Four of these patients had stereo-EEG implantation. Of the four patients studied, each had a seizure semiology discordant with an ictal focus in the temporal lobe. Intracranial EEG assessment demonstrated, irrespective of this semiology, seizures originated from the anterior temporal pole. Seizures were observed to rapidly propagate to the orbitofrontal cortex, insula, temporo-occipital junction, and posterior language regions. Engagement of the mesial temporal structures could occur early or late, however, a good surgical outcome was achieved following a focused lesionectomy in either situation. The major finding was that seizures arising from anterior temporal encephaloceles can have an extra-temporal semiology. The varied clinical semiology and the rapid propagation to seemingly distant cortical regions could be explained by the connectivity of the anterior temporal lobe.

Use of intraosseous hypertonic saline in critically ill patients.

BACKGROUND: Rapid administration of hypertonic saline 23.4% is crucial in treatment of herniation syndromes. Hypertonic 23.4% saline must be administered via a central line. In cases where central line access is difficult to obtain and leads to delay in therapy, placement of intraosseous access can be lifesaving. MAIN BODY: The purpose of this case series is to describe the use of intraosseous administration of 23.4% saline in critically ill patients and to assess feasibility. CONCLUSION: Intraosseous administration of 23.4% saline in 6 adult patients with neurological emergencies was feasible and should be considered in cases where obtaining intravenous access is time consuming.

Intradiploic encephalocele of the primary motor cortex in an adult patient: electrophysiological implications during surgery.

Encephaloceles are herniations of brain parenchyma through congenital or acquired osseous-dural defects of the skull base or cranial vault. Different types of symptoms, due to CSF fistulas, meningitis, or seizures, are often associated with this condition. The authors present a rare case of spontaneous right frontal parasagittal encephalocele in a 70-year-old man who was experiencing a spastic progressive paresis of his left lower limb. Results of routine electrophysiological workup (motor evoked potentials, somatosensory evoked potentials, and electroneuromyography), as well as those of MRI of the spinal cord, were normal. A brain MRI study detected a partial herniation of the right precentral gyrus through a meningeal defect into the diploe, embedding corticospinal fibers. The patient underwent navigated craniotomy. Intraoperative neuromonitoring of motor function with transcranial electrical stimulation and direct cortical stimulation indicated the presence of motor cortex inside the encephalocele. Thus, the brain parenchyma was carefully released without resection to preserve motor function and, finally, a cranioplasty was performed. After a few months, the patient demonstrated considerable improvement in his left lower-limb function and, after 1 year, he had fully recovered. Intraoperative electrophysiological monitoring and mapping allowed for the determination of the best surgical strategy for the isolation of the encephalocele and correlated well with preoperative multimodal MRI.

Intradural pathology and pathophysiology associated with Chiari I malformation in children and adults with and without syringomyelia.

OBJECTIVE The pathophysiology underlying tonsillar herniation and CSF obstruction in Chiari malformation Type I (CM-I) is unclear, and the cause of CM-I-associated syringomyelia is not well understood. A better understanding of this pathophysiology is important for an improved treatment strategy. Therefore, the authors sought to identify, characterize, and examine the intradural pathology and CSF flow pathophysiology in the posterior fossa and at the level of the foramen magnum that occurs in the setting of CM-I. They determined the incidence of these intradural findings and assessed differences across age, with the degree of tonsillar herniation, and in the presence and absence of syringomyelia. METHODS A prospective database initiated in March 2003 recorded all intraoperative findings during surgical treatment of children and adults with CM-I with or without syringomyelia. A total of 389 surgeries for CM-I were performed in 379 patients between March 2003 and June 2016. A total of 109 surgeries were performed in 109 patients with CM-I (without osseoligamentous abnormalities) in whom both a posterior fossa extradural and intradural decompression with duraplasty was performed (first-time intradural procedures). Using a surgical microscope, intradural pathology and obstruction of CSF channels were identified and assessed. Student t-tests and Fisher's exact tests compared groups in a series of univariate analyses, followed by multivariate logistic regression. RESULTS The following intradural pathological entities were observed (prevalence noted in parentheses). These include those that did not obstruct CSF flow channels: opacified arachnoid (33.0%), thickened arachnoid (3.7%), ischemic and gliotic tonsils (40.4%), tonsillar cysts (0.9%), and inferior descent of the fourth ventricle and cervicomedullary junction (CMJ) (78.0%). The following intradural pathological entities were observed to obstruct CSF flow channels: medialized tonsils (100%), tonsil overlying and obstructing the foramen of Magendie (21.1%), intertonsillar and tonsil to CMJ arachnoid adhesions (85.3%), vermian posterior inferior cerebellar artery branches obstructing the foramen of Magendie (43.1%), and arachnoid veils or webs obstructing or occluding the foramen of Magendie (52.3%). Arachnoid veils varied in type and were observed in 59.5% of patients with CM-I who had syringomyelia, which was significantly greater than the 33.3% of patients with CM-I without syringomyelia who had an arachnoid veil (p = 0.018). The presence of CM-I with an arachnoid veil had 3.22 times the odds (p = 0.013, 95% CI 1.29-8.07, by multivariate logistic regression) of being associated with syringomyelia, adjusting for tonsillar herniation. The inferior descent of the fourth ventricle and CMJ occurred with a greater degree of tonsillar herniation (p < 0.001) and correlated with a cervicomedullary kink or buckle on preoperative MRI. CONCLUSIONS Intradural pathology associated with CM-I with or without syringomyelia exists in many forms, is more prevalent than previously recognized in patients of all ages, and may play a role in the pathophysiology of CM-I tonsillar herniation. Arachnoid veils appear to partially obstruct CSF flow, are significantly more prevalent in cases of CM-I with syringomyelia, and therefore may play a role in the pathophysiology of CM-I-associated syringomyelia.

DIAGNOSIS OF ENDOCRINE DISEASE: Primary empty sella: a comprehensive review.

Primary empty sella (PES) is characterized by the herniation of the subarachnoid space within the sella, which is often associated with variable degrees of flattening of the pituitary gland in patients without previous pituitary pathologies. PES pathogenetic mechanisms are not well known but seem to be due to a sellar diaphragm incompetence, associated to the occurrence of upper sellar or pituitary factors, as intracranial hypertension and change of pituitary volume. As PES represents in a majority of cases, a neuroradiological findings without any clinical implication, the occurrence of endocrine, neurological and opthalmological symptoms, due to the above describes anatomical alteration, which delineates from the so called PES syndrome. Headache, irregular menses, overweight/obesity and visual disturbances compose the typical picture of PES syndrome and can be the manifestation of an intracranial hypertension, often associated with PES. Although hyperprolactinemia and growth hormone deficit represent the most common endocrine abnormalities, PES syndrome is characterized by heterogeneity both in clinical manifestation and hormonal alterations and can sometime reach severe extremes, as occurrence of papilledema, cerebrospinal fluid rhinorrhea and worsening of visual acuity. Consequently, a multidisciplinary approach, with the integration of endocrine, neurologic and ophthalmologic expertise, is strongly advocated and recommended for a properly diagnosis, management, treatment and follow-up of PES syndrome and all of the related abnormalities.

Expanding the allelic disorders linked to TCTN1 to include Varadi syndrome (Orofaciodigital syndrome type VI).

Varadi syndrome is a subtype of orofaciodigital syndrome (OFDS) that combines the typical features of OFDS and the posterior fossa features of Joubert syndrome. The only gene known to be mutated in Varadi syndrome is C5ORF42. In this report, we describe the phenotype of a patient with Varadi syndrome who is homozygous for a previously reported mutation in TCTN1 (NM_001082538.2:c.342-2A>G, p.Gly115Lysfs*8) and suggest that allelic disorders linked to TCTN1 include Varadi syndrome, in addition to Joubert syndrome and Meckel-Gruber syndrome.

Growth and Psychological Development in Postoperative Patients With Anterior Encephaloceles.

PURPOSE: Anterior encephaloceles are rare malformations that are frequently associated with other brain anomalies. This study evaluates the growth and psychological development of children following encephalocele repair. MATERIALS & METHODS: Growth and psychological assessment was done in 24 children with only encephalocele (group I); nine children with encephalocele and hydrocephalus (group II); seven children with encephalocele, hydrocephalus, and secondary malformations (group III); and 40 apparently healthy control subjects. Psychological assessment was done by evaluating intelligence and temperament. RESULTS: Single-stage repair was performed in 38 children, and two underwent multistage repair. Major postoperative complications were noted in three individuals. The follow-up period ranged from 12 to 168 months, and during this time the growth velocity declined significantly among group II and group III patients when compared with control subjects. After adjusting the body mass index for age, our data revealed that group III participants had a significantly (P = 0.02) lower body mass index than the control group. Group III also had poor indices for intelligence quotient (P ≤ 0.01) and temperament (P ≤ 0.01). Female patients had lower temperament indices when compared with unaffected females with regard to approach withdrawal (P ≤ 0.01), mood (P = 0.026), and intensity (P = 0.03). Overall, increased disease severity adversely affected the psychological indices. CONCLUSION: Individuals with anterior encephalocele without associated intracranial defects had excellent postoperative outcomes in terms of growth and psychological developments. Hydrocephalus and agenesis of corpus callosum had the least impact on psychological development. However, the presence of secondary brain defects led to developmental delays. Gender differences in temperament may suggest a need for distinct treatment regimens to assess psychosocial well-being for males and females.

Diagnostic use of computational retrotransposon detection: Successful definition of pathogenetic mechanism in a ciliopathy phenotype.

Among more than 5,000 human monogenic disorders with known causative genes, transposable element insertion of a Long Interspersed Nuclear Element 1 (LINE1, L1) is known as the mechanistic basis in only 13 genetic conditions. Meckel-Gruber syndrome is a rare ciliopathy characterized by occipital encephalocele and cystic kidney disease. Here, we document a boy with occipital encephalocele, post-axial polydactyly, and multicystic renal disease. A medical exome analysis detected a heterozygous frameshift mutation, c.4582_4583delCG p.(Arg1528Serfs*17) in CC2D2A in the maternally derived allele. The further use of a dedicated bioinformatics algorithm for detecting retrotransposon insertions led to the detection of an L1 insertion affecting exon 7 in the paternally derived allele. The complete sequencing and sequence homology analysis of the inserted L1 element showed that the L1 element was classified as L1HS (L1 human specific) and that the element had intact open reading frames in the two L1-encoded proteins. This observation ranks Meckel-Gruber syndrome as only the 14th disorder to be caused by an L1 insertion among more than 5,000 known human genetic disorders. Although a transposable element detection algorithm is not included in the current best-practice next-generation sequencing analysis, the present observation illustrates the utility of such an algorithm, which would require modest computational time and resources. Whether the seemingly infrequent recognition of L1 insertion in the pathogenesis of human genetic diseases might simply reflect a lack of appropriate detection methods remains to be seen.

A standardized method to measure brain shifts with decompressive hemicraniectomy.

BACKGROUND: A standardized, reliable, and practical method for measuring decompressive hemicraniectomy (DHC) defects and brain shifts in malignant middle cerebral artery (MCA) territory infarction is needed for reliable comparisons between computed tomography (CT) scans. Such a method could facilitate further studies on the effects of DHC. NEW METHOD: We describe and apply a method for measuring DHC defects and brain shifts on CT scans in 25 patients with malignant MCA territory infarction. Craniectomy area is adjusted for variations in head size, CT slice orientation is standardized, and the site of each measurement is defined. This method uses standard radiology platforms and volume-acquired helical CT scans. RESULTS: The measurements include a DHC size index (adjusted for variations in head size), midline brain shift (subfalcine), outward brain herniation (transcalvarial), and the diameter of the contralateral atrium of the lateral ventricle. Inter-rater agreement for these measurements in a sample of 15 subjects is excellent (correlation coefficients 0.90-0.98). COMPARISON WITH EXISTING METHODS: In contrast to previously reported methods, this method is tested in acute stroke patients, compensates for variability in head size, and includes a midline brain shift (subfalcine) and brain ventricular system measurements. CONCLUSIONS: A practical method for measuring DHC size and brain shifts designed to be consistent between scans is proposed. This method should facilitate comparisons of measurements between serial scans, between patients, and perhaps between studies. This method could be useful in medical and surgical studies of brain herniations in malignant MCA territory infarction, and possibly other conditions.

A Case of Evolving Bilateral Sphenoidal Meningoencephaloceles: Case Report and Review of the Literature.

BACKGROUND: The evolution of sphenoid sinus meningoencephaloceles and cerebrospinal fluid (CSF) rhinorrhea is poorly understood. CASE DESCRIPTION: We present a case demonstrating the gradual evolution of encephaloceles from both the lateral walls of a previously normal sphenoid sinus in a patient with dural arteriovenous fistula; the CSF leak that developed after staged embolization of the dural arteriovenous fistula was managed by an endoscopic endonasal transpterygoid approach. CONCLUSIONS: We suggest that over a period of time, chronic elevation of intracranial pressure can result in gradual erosion of the lateral wall of the sphenoid with development of meningoencephaloceles and CSF leaks.

Biometry, optical coherence tomography, and further clinical observations in Knobloch syndrome.

PURPOSE: Knobloch syndrome is a pathognomonic vitreo-retinopathy that includes zonular weakness, high myopia, and a distinct fundus appearance with tessellation out of proportion to the degree of myopia. Whether myopia in Knobloch syndrome is axial or lenticular is unclear. Also not known are the optical coherence tomography (OCT) correlates to the distinct fundus appearance. In this study we assess cycloplegic refraction, biometry, and macular spectral domain (SD) OCT in children with Knobloch syndrome. METHODS: A retrospective case series of seven children (12 eyes) with Knobloch syndrome. RESULTS: Twelve eyes with attached retinas (seven patients, aged 6-17 years old, mean 11 years) were identified, seven of which had OCT. Best-corrected vision was typically 20/300 or worse. Axial length divided by corneal radius was >3 for all eyes (3.23-3.77, mean 3.52), consistent with axial myopia, and axial lengths (26.58-30.27 mm, mean 28.16) were consistent with spherical equivalent degree of myopia (-10.00 to -18.50, mean -12) when compared to historical controls. OCT revealed lack of choriocapillaries, outer retinal disorganization, and lack of or only rudimentary foveal pit. CONCLUSIONS: Refractions and biometry in Knobloch syndrome are consistent with the myopia being axial. In addition to vitreo-retinopathy, choroidopathy is part of the phenotype and is an anatomical correlate to the distinctive fundus appearance.

Molecular and Clinical Findings in Patients With Knobloch Syndrome.

IMPORTANCE: Knobloch syndrome is a rare, recessively inherited disorder classically characterized by high myopia, retinal detachment, and occipital encephalocele, but it is now known to have an increasingly variable phenotype. There is a lack of reported electrophysiologic data, and some key clinical features have yet to be described. OBJECTIVE: To expand on current clinical, electrophysiologic, and molecular genetic findings in Knobloch syndrome. DESIGN, SETTING, AND PARTICIPANTS: Twelve patients from 7 families underwent full ophthalmic examination and retinal imaging. Further investigations included electroretinography and neuroradiologic imaging. Bidirectional Sanger sequencing of COL18A1 was performed with segregation on available relatives. The study was conducted from July 4, 2013, to October 5, 2015. Data analysis was performed from May 20, 2014, to November 3, 2015. MAIN OUTCOMES AND MEASURES: Results of ophthalmic and neuroradiologic assessment and sequence analysis of COL18A1. RESULTS: Of the 12 patients (6 males; mean age at last review, 16 years [range, 2-38 years]), all had high myopia in at least 1 eye and severely reduced vision. A sibling pair had unilateral high myopia in their right eyes and near emmetropia in their left eyes from infancy. Anterior segment abnormalities included absent iris crypts, iris transillumination, lens subluxation, and cataract. Two patients with iris transillumination had glaucoma. Fundus characteristics included abnormal collapsed vitreous, macular atrophy, and a tesselated fundus. Five patients had previous retinal detachment. Electroretinography revealed a cone-rod pattern of dysfunction in 8 patients, was severely reduced or undetectable in 2 patients, and demonstrated cone-rod dysfunction in 1 eye with undetectable responses in the other eye in 2 patients. Radiologic imaging demonstrated occipital encephalocele or meningocele in 3 patients, occipital skull defects in 4 patients, minor occipital changes in 2 patients, and no abnormalities in 2 patients. Cutaneous scalp changes were present in 5 patients. Systemic associations were identified in 8 patients, including learning difficulties, epilepsy, and congenital renal abnormalities. Biallelic mutations including 2 likely novel mutations in COL18A1, were identified in 6 families that were consistent with autosomal recessive inheritance with a single mutation identified in a family with 2 affected children. CONCLUSIONS AND RELEVANCE: This report describes new features in patients with Knobloch syndrome, including pigment dispersion syndrome and glaucoma as well as cone-rod dysfunction on electroretinography. Two patients had normal neuroradiologic findings, emphasizing that some affected individuals have isolated ocular disease. Awareness of the ocular phenotype may aid early diagnosis, appropriate genetic counseling, and monitoring for potential complications.

Chiari Type 1 Deformity in Children: Pathogenetic, Clinical, Neuroimaging, and Management Aspects.

Our understanding of cerebellar tonsillar herniation evolved over time and nowadays various pathomechanisms have been proposed. Causes of tonsillar herniation share a discrepancy between content (fore- and hindbrain) and container (supratentorial cranial vault, posterior fossa), may be associated with abnormalities of the craniocervical junction, and may have a developmental or acquired nature. In tonsillar herniation, the hindbrain is not malformed but deformed. Accordingly, "Chiari type 1 deformity," not "Chiari type 1 malformation" is the correct term to characterize primary tonsillar herniation. Chiari type 1 deformity is commonly seen in pediatric neurology, neuroradiology, and neurosurgery and may have various clinical presentations depending on patient age. In addition, Chiari type 1 deformity is increasingly found by neuroimaging studies as an incidental finding in asymptomatic children. An accurate and reliable selection of patients based on clinical and neuroimaging findings is paramount for the success of neurosurgical treatment. Future studies are needed to provide selection criteria with a higher sensitivity and specificity.

[Prenatal diagnosis of Meckel-Gruber syndrome. Case report and literature review]. / Diagnóstico prenatal de síndrome de Meckel-Gruber. Reporte de un caso y revisión de la bibliografía.

BACKGROUND: Meckel-Gruber syndrome is a ciliopathy, a lethal autosomal recessive disorder that occurs in all races and ethnicities; it is characterized by central nervous system abnormalities, resulting in mental retardation, bilateral renal cystic dysplasia and malformations of hands and feet. To date there have been only about 200 cases reported worldwide. It is a disease with a recurrence rate of 25% whose most reliable method for diagnosis is prenatal ultrasound. The mortality rate is 100% and in view of the high index of recurrence, subsequent pregnancies should be investigated appropriately with genetic counseling. CLINIC CASE: We present the case of a 15 years-old mother with 30.2 weeks pregnancy resulting from rape by consanguinity (grandfather), without prenatal care. On admission HD ultrasound study is performed finding fetus fetometria average 26.2 weeks (for discordant fetometria head circumference 187.5 mm to 21.0 weeks gestation -3DE-) lost in the skull shape of the shell line is observed winding mean; not cut down, cavum septum pellucidum or herniated sac cerebellum and occipital level (encephalocele) are evident. It starts cervical ripening with prostaglandins for 24 hours to conduct further labor with oxytocic and delivery care where a fetus death, female, 1516 g is obtained. Fetal autopsy family is authorized; however, it not has done because it is legal and only medical geneticist obtains medical case assessment. CONCLUSIONS: The Meckel-Gruber syndrome is a very rare condition that occurs in cases of consanguinity occasions. Mortality occurs in 100% of cases, so you should talk to parents and explain the best maternal prognosis, with abortion in the early stages and subsequent genetic counseling.

Neurological outcomes in Chiari type II malformations and their correlation to morphological findings and fetal heart rate patterns: a retrospective study.

BACKGROUND: Correlations among Chiari type II malformation (CMII) morphological findings, the proportion of fetal heart rate patterns corresponding to the quiet phase (QP), and neurological outcomes have yet to be investigated. FINDINGS: The correlations among the morphological findings (i.e., the degree of ventriculomegaly, myelomeningocele levels, and degree of cerebellar herniation), proportion of time spent in QP, and developmental quotients (DQs) were analyzed in 22 children. The proportion of time spent in QP was compared between children with poor neurological outcomes (n = 9) and those with good outcomes (n = 13). Pearson's correlations and the Mann-Whitney U-test were used to assess for statistical significance; P < 0.05 was considered statistically significant. No significant differences were observed between the DQs and morphological findings, but the DQs and the proportion of time spent in QP were significantly correlated (r = 0.287, P = 0.01). The proportion of time spent in QP was significantly different between children with poor outcomes and those with good outcomes (median, 11% [range, 0-32%] vs. 28% [range, 2-55%]; P = 0.006). CONCLUSIONS: The proportion of fetal heart rate patterns corresponding to the QP might be a useful predictor of neurological outcomes in 2-year-old children with CMII.

Herniación paradójica transtentorial, manifestación extrema del síndrome del craniectomizado. Caso clínico / Paradoxical transtentorial herniation, extreme trephined syndrome sign: A case report

El creciente auge actual del uso de la craniectomía descompresiva conlleva implícita la aparición de complicaciones derivadas de la alteración en la presión barométrica intracraneal y del equilibrio tanto hidrostático como hemodinámico. La herniación paradójica transtentorial («paradoxycal transtentorial herniation») representa una rara manifestación, englobada dentro del síndrome del craniectomizado, de extrema gravedad y de tratamiento relativamente simple. Presentamos el caso de una mujer de 56 años, sin antecedentes de interés, que tras ser intervenida de un meningioma del surco olfatorio presenta un hematoma en el lecho quirúrgico con abundante edema, requiriendo una segunda intervención de urgencia sobre este sin posibilidad de realizar la reposición ósea. Durante el posoperatorio se observa un gran deterioro neurológico de la paciente con el ortostatismo, que se resolvía espontáneamente con el decúbito y que se solventa con la reposición ósea posteriormente. Se analizan los posibles factores predisponentes y las posibles etiologías del cuadro

The current increasing use of decompressive craniectomy carries the implicit appearance of complications due to alterations in both intracranial pressure and in the hydrostatic-hemodynamic equilibrium. Paradoxical transtentorial herniation represents a rare manifestation, included in “trephine syndrome”, extremely critical but with relatively simple treatment. We present the case of a 56-year-old woman with no interesting medical history, who, after an olfactory groove meningioma surgery, presented a haemorrhage located in the surgical area with an important oedema. The patient required a second emergency surgery without any chance of conserving the cranial vault. During the post-operational period, great neurological deterioration in orthostatic position was noticed, which resolved spontaneously in decubitus. This deficit was resolved with bone replacement afterwards. We discuss possible predisposing factors and aetiologies of this pathology

Transcalvarial brain herniation volume after decompressive craniectomy is the difference between two spherical caps.

Decompressive craniectomy (DC) is a surgical procedure used to relieve severely increased intracranial pressure (ICP) by removing a portion of the skull. Following DC, the brain expands through the skull defect created by DC, resulting in transcalvarial herniation (TCH). Traditionally, people measure only changes in the ICP but not in the intracranial volume (ICV), which is equivalent to the volume of TCH (V(TCH)), in patients undergoing DC. We constructed a simple model of the cerebral hemispheres, assuming the shape of the upper half of a sphere with a radius of 8 cm. We hypothesized that the herniated brain following DC also conforms to the shape of a spherical cap. Considering that a circular piece of the skull with a radius of a was removed, V(TCH) is the volume difference between 2 spherical caps at the operated side and the corresponding non-operated side, which represents the pre-DC volume underneath the removed skull due to the bilateral symmetry of the skull and the brain. Subsequently, we hypothesized that the maximal extent of TCH depends on a because of the biomechanical limitations imposed by the inelastic scalp. The maximum value of V(TCH) is 365.0 mL when a is 7.05 cm and the height difference between the spherical caps (Δh) at its maximum is 2.83 cm. To facilitate rapid calculation of V(TCH), we proposed a simplified estimation formula, Vˆ(TCH)=1/2A(2)Δh, where A=2a. With the a value ranging between 0 and 7 cm, the ratio between Vˆ(TCH) and V(TCH) ranges between 0.77 and 1.27, with different Δh values. For elliptical skull defects with base diameters of A and C, the formula changes to Vˆ(TCH)=1/2ACΔh. If our hypothesis is correct, surgeons can accurately calculate V(TCH) after DC. Furthermore, this can facilitate volumetric comparisons between the effects of DCs in skulls of varying sizes, allowing quantitative comparisons between ICVs in addition to ICPs.