Chiari malformation (CM) is primarily characterised by herniation of the cerebellar tonsils through the foramen magnum. Clinically, two main types of CM represent the vast majority of cases: type I (in adults) and type II (in infants). CM may result in neuronal impairment of the brainstem, upper spinal cord and cranial nerves. Part of the afferent and efferet systems and the central respiratory controlling system are located in the cranium-cervical transition and may be damaged in these pathologies, leading to respiratory disorders, such as respiratory failure and death. The ventilatory responses to exogenous and endogenous stimuli, such as responses to hypoxia and hypercapnia, are usually diminished, and apnea may be manifested and detected during sleep, allowing for the diagnosis. This study is a review of the relationship between sleep apnoea and adult CM.

To investigate overcrowding in the posterior cranial fossa as the pathogenesis of adult-type Chiari malformation, the authors studied the morphology of the brainstem and cerebellum within the posterior cranial fossa (neural structures consisting of the midbrain, pons, cerebellum, and medulla oblongata) as well as the base of the skull while taking into consideration their embryological development. Thirty patients with Chiari malformation and 50 normal control subjects were prospectively studied using neuroimaging. To estimate overcrowding, the authors used a "volume ratio" in which volume of the posterior fossa brain (consisting of the midbrain, pons, cerebellum, and medulla oblongata within the posterior cranial fossa) was placed in a ratio with the volume of the posterior fossa cranium encircled by bony and tentorial structures. Compared to the control group, in the Chiari group there was a significantly larger volume ratio, the two occipital enchondral parts (the exocciput and supraocciput) were significantly smaller, and the tentorium was pronouncedly steeper. There was no significant difference in the posterior fossa brain volume or in the axial lengths of the hindbrain (the brainstem and cerebellum). In six patients with basilar invagination the medulla oblongata was herniated, all three occipital enchondral parts (the basiocciput, exocciput, and supraocciput) were significantly smaller than in the control group, and the volume ratio was significantly larger than that in the Chiari group without basilar invagination. These results suggest that in adult-type Chiari malformation an underdeveloped occipital bone, possibly due to underdevelopment of the occipital somite originating from the paraxial mesoderm, induces overcrowding in the posterior cranial fossa, which contains the normally developed hindbrain. Basilar invagination is associated with a more severe downward herniation of the hindbrain due to the more severely underdeveloped occipital enchondrium, which further exacerbates overcrowding of the posterior cranial fossa.

Three generations of a family affected by a craniocervical malformation (CCM) were subjected to clinical and radiological studies. Occipital dysplasia (OD) and Chiari type I deformity (CD.I) were the main features, inheritance being autosomal-dominant. The malformation was variably expressed; it ranged from OD with basilar impression (BI) to OD without BI and from CD.I with OD to CD.I without obvious osseous malformation. Its pathogenesis, and that of other related familial disorders (Klippel-Feil syndrome and syringomyelia), is discussed, the conclusion being drawn that all were elements of one genetic disorder which finds expression in a very variable sequence. The value of high-resolution CT in the detection of asymptomatic carriers is emphasized.

The authors report their recent experience with 14 meningomyelocele patients with the Arnold-Chiari II malformation. Three major types of fourth ventricle anomalies seen in the Arnold-Chiari II malformation are defined, based on preoperative magnetic resonance imaging and intraoperative ultrasound studies. The Type A deformity is defined as no cystic dilatation of the fourth ventricle. In the Type B anomaly, there is intracranial dilatation of the fourth ventricle. The Type C deformity involves intraspinal dilatation of the fourth ventricle, either dorsal to the cord or within the substance of the cord. The Type A deformity was most common in infants, and in two cases progression from a Type A to Type B deformity was documented. Recognition of the type of Arnold-Chiari II malformation aids in designing an operative approach more specific to that structural abnormality. Intraoperative ultrasound is a valuable adjunct in localization of the underlying anomalies and permits safe decompression of the fourth ventricle. The authors' indications for surgery now include failure to thrive due to either early respiratory and swallowing dysfunction, progressive spasticity, or upper-extremity weakness. Nine patients significantly improved following surgery and three patients with a progressively deteriorating course were stabilized by surgery. Decompression of the fourth ventricle by fenestration and internal shunting appears to be well tolerated, even in young infants, and is recommended in the treatment of the Arnold-Chiari II deformity.

In the Chiari II deformity, the following defects can be visualized by computed tomography: partial or complete fusion of the corpora quadrigemina into a tectal beak or spur and invagination of the midline cerebellum to receive this spur; marked upward, transincisural growth of the cerebellum to produce a supratentorial,"extra-axial" mass effect (especially after shunting); enlargement of the pericerebellar cistern about the "towering" cerebellum, and infolding of the anterior border of the towering cerebellum to overlap the vermis and the more caudal portions of the cerebellum. Growth of the cerebellar hemispheres around the brain stem results in (a) overlapping of more of the cerebral peduncles than usual, which sometimes separates the midbrain from the hippocampus;(b) overlapping of more of the lateral aspect of the pons than usual, causing partial filling in of the cerebellopontine angle (CPA) cisterns, presenting as bilateral CPA masses, and (c) wedging of the cerebellar margin between the lateral aspect of the brain stem and the adjacent free tentorial margin, so that the cerebellar hemispheres acquire an anteriorly pointed configuration.

A total of 20 patients with an Arnold-Chiari Type I malformation, i.e. without skeletal abnormality and associated with a syringomyelic syndrome, were studied using the EMI Whole Body Scanner CT5000. Two groups were considered:(i) a retrospective series of 12 patients without intrathecal water soluble contrast media and (ii) a prospective series of eight patients after the introduction of intrathecal Metrizamide. In the first group tonsillar herniation could not be conclusively identified on CT and cord visualisation was possible in only two cases. In the second group, tonsillar herniation and cord expansion were consistently demonstrated. Cord cavitation has also been detected. In both groups it was possible to assess the size and position of the ventricular system. The results of this study indicate that evaluation of the upper cervical cord cerebellar tonsillar herniation, may be achieved, but only following opacification of the CSF. The precise extent of cerebellar tonsillar herniation may be difficult to evaluate. The reasons for these findings are discussed.

STUDY DESIGN: In this retrospective study, a 5-year series of a pediatric population undergoing Chiari decompressions is reviewed. OBJECTIVES: To review the experience with children treated with suboccipital craniectomy and uni- or multilevel cervical laminectomy for Chiari malformation, to determine the incidence of kyphosis and to identify factors predictive of cervical instability. SUMMARY OF BACKGROUND INFORMATION: Upper cervical laminectomy in the pediatric population has a significant risk of postoperative kyphosis. To decrease the incidence of this complication, a concerted effort was made to avoid violation of the facet joint during cervical laminectomy. METHODS: Thirty-two patients (mean age 4.9 years, range 1 day to 18 years) had surgical decompression of Chiari I or II malformations throughout a 5-year period (1989-1994). Radiographs and operative records were analyzed to determine the number of cervical levels decompressed and extent of laminectomy. RESULTS: Mean follow-up was 3.7 years (range 9 months to 7 years). Only one patient had clinical and radiographic evidence of kyphosis and required C2-C3 fusion. Two others had radiographic signs of mild cervical kyphosis but remained asymptomatic. These three patients had two-level complete laminectomies. Twenty-nine patients had no clinical or radiographic evidence of cervical instability. A mean of three cervical levels were decompressed (range 0-4), including partial laminectomies, complete laminectomies, and one osteoplastic laminotomy to drain a lower cervical syrinx. The overall frequency of kyphosis in this series (9%) was substantially lower than in previous reports. Although the number of cervical levels decompressed did not correlate with cervical instability, the one patient with clinical instability had inadvertent violation of the facet joint, suggesting that overaggressive laminectomy may be a critical factor that predisposes patients to postoperative kyphosis. CONCLUSION: Cervical kyphosis after Chiari decompression is a recognized complication of cervical laminectomy in children, the frequency of which may be decreased by careful attention to operative technique.

A series of 3,500 cases examined by computed tomography (CT) of the head were reviewed to identify patients who had symptoms and signs suggestive of neurologic disease in the posterior fossa. Three hundred forty eight such cases (about 10%) were found, and the scans were reviewed to determine the character of lesions that could be detected and the accuracy of the neuroradiologic diagnosis. Overall, 16 errors were made (4.6%), of which 13 were false negatives and 3 were false positives. False negatives included nine tumors, two infarcts, and two arteriovenous malformations. Four of the tumors and the two arteriovenous malformations were small and caused no visible alterations in density even when analyzed retrospectively. In the remaining seven cases, specific findings either were overlooked or were obscured by artifacts, and, therefore, the diagnosis was not made. The three false positive diagnoses were made through a misinterpretation of density changes that were artifactual. No changes in the intracranial absorption coefficients were detected in 109 cases. Abnormal changes were evident in 226 cases in which structural lesions were subsequently found. Many of the lesions had a characteristic appearance, but in certain clinical situations, which include searches for metastatic disease, acoustic neuromas, meningiomas aneurysms of the basilar artery, and arteriovenous malformations, the injection of intravenous contrast medium was helpful, or even essential, for diagnostic success. The prominence of clinical signs and symptoms is not always an accurate index to the presence of structural alteration of the posterior fossa. We believe, therefore, that this portion of the cranium should be included in every CT study.

Forty adult patients (average age 40 years), with the clinical and radiological features of the Chiari malformations, were seen at the Toronto Western Hospital between 1967 and 1984. Surgical confirmation of the diagnosis was obtained in 32 cases; of these, 23 were classified as Chiari I malformation while 9 fulfilled the anatomic criteria of Chiari II. The patient population consisted of 22 males and 18 females. Common presenting symptoms included head and neck pain (60%), sensory complaints (60%), upper extremity weakness (42%), and gait disturbance (40%). Neurological findings included signs of central cord dysfunction (73%), long-tract motor and/or sensory findings (58%), brainstem signs (38%), cerebellar dysfunction (18%), and increased intracranial pressure (15%). The majority of patients underwent myelography with or without computed tomography of the cervical-medullary junction. Two recent patients had 0.15T MRI scans which helped demonstrate an intramedullary syrinx. Thirty-three patients underwent 47 operative procedures (discounting spinal fusion and CSF shunt revisions). Open surgical management was performed in 32 patients, with CSF shunting along in one patient. Five patients (15%) incurred surgical complications within a six week postoperative period. Follow-up to date, ranges from one month to 11 years. In the 33 surgically treated patients, 18 are improved (55%), 10 are neurologically stable (30%), and five have worsened clinically (15%), including one death. Based on this study it appears that the Chiari II malformation may be more common in adults than previously recognized. Surgical intervention has a favourable outcome in the majority of patients but a significant proportion continue to deteriorate.

Lückenschädel, scalloping of the posterior surface of the petrous pyramids, falx hypoplasia, falx fenestration, and tentorial hypoplasia with wide incisura and tiny posterior fossa are readily identified by computed tomography (CT) in patients with Chiari II malformation. Enlargement of the foramen magnum may be appreciated on axial section CT in some cases. None of these findings is pathognomonic and each may be observed in some patients with other conditions. In the aggregate, however, these findings strongly suggest the presence of Chiari II malformation.

The sagittal spine of children with Arnold-Chiari I malformation with or without syringomyelia and associated scoliosis (ACS) has been poorly studied. A retrospective review of scoliosis secondary to ACS from three centers was undertaken. Sagittal and coronal plane variables were measured from standing radiographs. There were 30 ACS children (19 girls, 11 boys) with an average curve of 50 +/- 20 degrees and age of 11.2 +/- 3.2 years. Syringomyelia was present in 26 (87%). The scoliosis was thoracic in 25, thoracolumbar in 3 and lumbar in 2; 18 curves were right and 12 were left. A positive correlation was noted between cervical lordosis (CL) and thoracic kyphosis (TK). The 30 children with ACS scoliosis were compared with 26 children with adolescent idiopathic scoliosis (AID). The ACS group had more left curves (40% vs. 0%, P = 0.0002), more boys (37% vs. 8%, P = 0.01), and was younger (11.3 +/- 3.7 years vs. 14.2 +/- 1.8 years, P = 0.004). TK and CL were increased in ACS (TK: 40 +/- 13 degrees vs. 30 +/- 13 degrees, P = 0.005; CL: 16 +/- 21 degrees vs.-5 +/- 12 degrees, P < 0.0001). The ACS and AID groups were subdivided by CL >0 degrees and <0 degrees. In the ACS group, 19%(5 of 21) had CL <0 degrees, in the AID group 77%(20 of 26) had CL <0 degrees (P = 0.0001). When cervical lordosis is >0 degrees or thoracic kyphosis is >40 degrees (Cobb method), the clinician should strongly suspect the presence of an Arnold-Chiari I malformation with or without syringomyelia.