No significant difference between chiari malformation type 1.5 and type I

Chiari I Deformity: Beyond 5 mm below the Foramen Magnum

Although originally described as a consecutive series of pathologic changes, Chiari syndrome represents a spectrum of disease divided into two subsets: development deformities of the paraxial mesoderm manifesting after birth (types 0-1.5) and true congenital malformations due to failure of neural tube closure present in utero (types 2-5). Heterogeneity among patients with a Chiari deformity and incomplete understanding of its pathophysiologic characteristics have led to inconsistency in radiologic reporting and difficulty in defining appropriate management strategies tailored to an individual patient's condition. The radiologist is tasked with going beyond the criteria for cerebellar tonsillar herniation to define an individual patient's disease state, determine candidacy for surgery, and assist in selecting the proper surgical approach. In addition, the radiologist must be able to identify conditions that result in cerebellar tonsillar herniation that are not related to Chiari deformity to avoid inappropriate surgery. Last, the radiologist must be able to interpret postoperative imaging examinations to assess for adequacy of treatment and complications. The authors summarize recent literature regarding the pathophysiologic basis of Chiari 1 and related deformities and detail the ideal morphologic and physiologic imaging assessment, focusing on Chiari 1 and related deformities (Chiari 0, 0.5, and 1.5). Also discussed are surgical techniques and "pearls" of postsurgical imaging, including complications that must be recognized. This review provides clarity to a commonly encountered but less understood condition to optimize outcomes for patients with Chiari 1 and related deformities. ©RSNA, 2024 Supplemental material is available for this article. See the invited commentary by Huisman in this issue.

Research process, recap, and prediction of Chiari malformation based on bicentennial history of nomenclature and terms misuse

There is an absent systematic analysis or review that has been conducted to clarify the topic of nomenclature history and terms misuse about Chiari malformations (CMs). We reviewed all reports on terms coined for CMs for rational use and provided their etymology and future development. All literature on the nomenclature of CMs was retrieved and extracted into core terms. Subsequently, keyword analysis, preceding and predicting (2023-2025) compound annual growth rate (CAGR) of each core term, was calculated using a mathematical formula and autoregressive integrated moving average model in Python. Totally 64,527 CM term usage was identified. Of these, 57 original terms were collected and then extracted into 24 core-terms. Seventeen terms have their own featured author keywords, while seven terms are homologous. The preceding CAGR of 24 terms showed significant growth in use for 18 terms, while 13, three, three, and five terms may show sustained growth, remain stable, decline, and rare in usage, respectively, in the future. Previously, owing to intricate nomenclature, Chiari terms were frequently misused, and numerous seemingly novel but worthless even improper terms have emerged. For a very basic neuropathological phenomenon tonsillar herniation by multiple etiology, a mechanism-based nosology seems to be more conducive to future communication than an umbrella eponym. However, a good nomenclature also should encapsulate all characteristics of this condition, but this is lacking in current CM research, as the pathophysiological mechanisms are not elucidated for the majority of CMs.

Anatomical Implications of Chiari I and Basilar Invagination (Type B) in the IV Ventricle and Cisterna Magna

OBJECTIVE

To analyze the anatomical changes of the IV ventricle and cisterna magna in the Chiari malformation I (CMI) and basilar invagination (type B).

METHODS

This is a controlled study with 161 exams of magnetic resonance imaging (MRI) of adults grouped into control (n = 37), basilar invagination (BI; n = 31), Chiari malformation I (CMI; n = 37), and CMI+BI (n = 56). The MRIs were analyzed using the visualization software Osirix (Pixmeo, Bernex, Geneva, version 3.8.2). The morphometric variables were: distance from the obex to the McRae line; length of the IV ventricle floor; and the area and volume of the cisterna magna. The univariate ANOVA followed by Tukey's post-hoc test was applied to evaluate the difference between the groups. The difference between sexes was evaluated by the t test for each group.

RESULTS

Alterations in the cisterna magna and IV ventricle were more evident only in the CMI and CMI+BI groups. For both sexes, the CMI and CMI+BI groups showed: a reduction in the CSF space (P < 0.001), cisterna magna with volume reduction (P < 0.001), low position of the obex (P < 0.001), and IV ventricle more elongated (male P = 0.007 and female P < 0.001). The BI group had no significant change in the analysis by sex.

CONCLUSIONS

The CMI (isolated and associated with BI) showed a low obex position and elongation of the IV ventricle due to traction towards the spinal canal. The reduction of cisterna magna volume added to the occupation of the cerebellar tonsils can impact in the cerebrospinal fluid dynamics. The BI when isolated was not related to alterations in the parameters of cerebrospinal fluid spaces studied.

Arnold Chiari malformation classified as Chiari 1.5 malformation in a Japanese black calf

A 2-day-old male black calf presented with neurological symptoms, including opisthotonus. It was unable to stand due to hindquarter paresis. At 5 days old, the calf was able to stand, but exhibited a crossed forelimb gait. Computed tomography and magnetic resonance imaging revealed the expansion of the sutures between the squamous-lateral part of the occipital bone and between the occipital-temporal bone, cerebellar tonsillar herniation, posterior displacement of the brainstem, and cervical syringomyelia at 12 days old. This is the first case report of a live calf diagnosed with Arnold Chiari malformation classified as Chiari type 1.5 malformation in humans.

Surgical outcomes of calvaria reconstruction in cranial pansynostosis associated with Arnold-Chiari type 1.5 malformation, a case report

A 6-year-old girl with persistent headaches and the visual problem was diagnosed as a delayed onset cranial pansynostosis with concurrent type 1.5 Arnold-Chiari malformation. She underwent multi-sutural reconstructive surgery and followed. The headache was greatly decreased and tonsillar-brain stem herniation and syrinx were resolved.

Chiari malformation type I surgery in children: French multicenter 10-year cohort

OBJECTIVE

Chiari malformation type I (CM-I) is frequent in children and remains a surgical challenge. Several techniques have been described for posterior fossa decompression. No decision algorithm has been validated, and strategies are highly variable between institutions. The goal of this study was to define therapeutic guidelines that take into consideration patient specificities.

METHODS

The authors retrospectively collected data from patients who were < 18 years of age, were diagnosed with CM-I, and were treated surgically between 2008 and 2018 in 8 French pediatric neurosurgical centers. Data on clinical features, morphological parameters, and surgical techniques were collected. Clinical outcomes at 3 and 12 months after surgery were assessed by the Chicago Chiari Outcome Scale. The authors used a hierarchical clustering method to define clusters of patients by considering their anatomical similarities, and then compared outcomes between surgical strategies in each of these clusters.

RESULTS

Data from 255 patients were collected. The mean age at surgery was 9.6 ± 5.0 years, syringomyelia was reported in 60.2% of patients, the dura mater was opened in 65.0% of patients, and 17.3% of patients underwent a redo surgery for additional treatment. The mean Chicago Chiari Outcome Scale score was 14.4 ± 1.5 at 3 months (n = 211) and 14.6 ± 1.9 at 12 months (n = 157). The hierarchical clustering method identified three subgroups with potentially distinct mechanisms underlying tonsillar herniation: bony compression, basilar invagination, and foramen magnum obstruction. Each cluster matched with specific outcomes.

CONCLUSIONS

This French multicenter retrospective cohort study enabled the identification of three subgroups among pediatric patients who underwent surgery for CM-I, each of which was associated with specific outcomes. This morphological classification of patients might help in understanding the underlying mechanisms and providing personalized treatment.

Case of simultaneous Chiari 1.5 malformation and syringobulbia

Chiari 1.5 malformation (C1.5) is a rare condition characterized by caudal descent of the brain stem, together with descent of the cerebellar tonsils characteristic of Chiari I malformation (CIM). Syringobulbia (SB) is rarely associated with CIM and to date has not been reported in a patient with C1.5. An adolescent female presented with Valsalva-induced headaches and a left abducens nerve palsy. Imaging revealed C1.5 and a huge syringomyelia extending cranially into the herniated medulla oblongata as syringobulbia. Simultaneous cases of C1.5 and syringomyelia (SM) have been described, but, to our knowledge, this is the first reported case of simultaneous C1.5 and SB. As SB can have life altering consequences, the clinician should keep this possibility in their differential diagnosis.

Chiari type 1-a malformation or a syndrome? A critical review

OBJECTIVE

As the understanding of pathophysiology behind Chiari malformation still is limited, the treatment of Chiari malformation type 1 remains rather empirical. This may result in suboptimal treatment strategy and outcome in many cases. In this review, we critically address whether the condition known today as Chiari malformation type I should rather be denoted Chiari syndrome.

METHODS

The current knowledge of Chiari malformation type 1 is summarized from the historical, etymological, genetic, clinical, and in particular pathophysiological perspectives.

RESULTS

There are several lines of evidence that Chiari malformation type 1 represents a condition significantly different from types 2 to 4. Unlike the other types, the type 1 should rather be considered a syndrome, thus supporting the reasons to reappraise the traditional classification of Chiari malformations.

CONCLUSION

We propose that Chiari malformation type 1 should rather be denoted Chiari syndrome, while the notation malformation is maintained for types 2-4.

Ventrolateral Tonsillar Position Defines Novel Chiari 0.5 Classification

BACKGROUND

Cervicomedullary compression in young children has been described in the context of Chiari type 1 malformation, with symptoms associated with the extent of tonsillar herniation below McRae line. Historically, Chiari type 1 malformation has been defined by tonsillar herniation of at least 5 mm. However, in certain populations, including very young children, Chiari symptoms may be present without this finding. A new Chiari classification is thus necessary.

METHODS

Cases involving patients up to 5 years of age evaluated for possible posterior fossa decompression were retrospectively reviewed. Preoperative symptoms, magnetic resonance imaging findings, surgical management, and short- and long-term outcome and follow-up were recorded. Tonsillar descent and presence of ventral herniation (VH) were recorded. We define VH as the tonsils crossing a line that bisects the caudal medulla at the level of the foramen magnum, thus creating a novel entity, Chiari type 0.5 malformation. Patients with ventrally herniated tonsils were compared with patients exhibiting more typical Chiari morphology.

RESULTS

Of 41 cases retrospectively reviewed, 20 met criteria for VH. These differed from cases without VH because of the predominance of medullary symptoms. In the VH cohort, 11 patients underwent surgical decompression with symptom resolution; 9 were initially managed conservatively, but 3 subsequently required surgery.

CONCLUSIONS

We define a novel Chiari entity, Chiari type 0.5 malformation, characterized by ventral tonsillar wrapping around the medulla in young children in the absence of classic Chiari type 1 malformation imaging findings. These patients are more likely to present with medullary symptoms than patients without VH. They are also more likely to require surgical decompression and respond favorably to intervention.

Management: opinions from different centers-the Istituto Giannina Gaslini experience

PURPOSE

Describe presentation and management of Chiari type 1 malformation. We report our surgical case series proposing a decision making scheme for helping surgeons decide which surgical procedure to perform and when.

METHODS

We retrospectively examined a series of surgically treated patients with Chiari type 1 malformation. Treatment of associated anomalies, surgical complications, and need for reintervention for insufficient decompression at first surgery are discussed.

RESULTS

A total of 172 patients have been surgically treated for Chiari type 1 malformation at the Neurosurgery Unit of IRCCS Giannina Gaslini Children Hospital of Genoa, Italy, in a period between 2006 and 2017. The first treatment addressing Chiari type 1 malformation was bone and ligamentous decompression alone in 104 patients (65%), associated with dural delamination in 3 patients (1.9%) and associated with duraplasty with autologous graft in 53 patients (33.1%). Postoperative complications occurred in 5 patients (2.9%). Reintervention for insufficient decompression at follow-up was needed in 6 patients (3.5%).

CONCLUSIONS

Surgical decompression of the posterior cranial fossa (PCF) is indicated in symptomatic patients while asymptomatic patients must be followed in a wait and see fashion. Different types of surgical decompression of different invasiveness have been proposed from only bone and ligamentous decompression to coagulation of cerebellar tonsils. Intraoperative ultrasonography is a useful tool to define when a decompression is sufficient. We did not find correlation between the need for reintervention for insufficient decompression and different invasiveness of the techniques. We believe that this finding suggests that our proposed scheme leads to the best tailored treatment for the single patient.