During a fourteen-year period 1989–2002, 50 patients with the diagnosis of Chiari malformation without myelodysplasia (i.e., with the diagnosis of hindbrain malformation) underwent surgery at the Department of Neurosurgery of Masaryk Hospital in Ústí nad Labem and later at the Clinic of Neurosurgery of the First Faculty of Medicine, Charles University and IPVZ, Prague. Based on MR imaging, the patients were subdivided into groups according to disease grade (I, II) or spine findings (A – syringomyelia present, B – syringomyelia absent). Most of patients in group A had signs of central lesion of the spine which dominated in the clinical picture over cerebellar and brain stem signs or manifestations of increased intracranial pressure, which were present as well. In group B, manifestations of intracranial hypertension and cerebellar signs dominated. In all cases, we have performed decompression of foramen magnum. In patients from group A, we have performed intradural revision with lysis of arachnoideal adhesions if they blocked CSF circulation. In some patients (before the year 1996), we additionally blocked the central canal with a piece of muscular mass and drained the fourth ventricle with a short shunt subarachnoideally into the level of upper cervical spine. In some patients with hydrocephalus or syringomyelia,we have performed a secondary procedure: various types of syringeal or ventricular drainage and shunting. Results were satisfactory in most patients of group B (20 improved, 3 stabilized,none worsened), in group A,improvement or stabilization occurred in 20 patients (10 improved, 10 stabilized), in 7 patients the status deteriorated further. Patients with spinal disease (Chiari malformation type A) have more severe course and prognosis than patients with valve or cerebellarmanifestations.This results from syringomyelic cavity damaging the spine, which more often accompanies the higher type of malformationaccording to the classic classification(I–IV).This supports the view that classification A/B according to the presence or absence of syringomyelic cavity has more clinical significance than the classic classification according to Chiari. The study assumes that in group B, decompression of bony structures is a sufficient surgical procedure. In contrast, procedure of choice in group B was surgery according to Gardner and its modifications. In 1996, we changed the surgical methods in group A patients according to preliminary surgical data and first results of parallel CSF pressure measurement in the head and lumbar spine (these results were published elsewhere). The main conclusion of evaluations in this group of surgically treated patients with hindbrain malformation remain as follows: 1. arrest of disease progression can be considered a success in group A (syringomyelia present), 2. but in group B (syringomyelia absent), mere stabilization without other effects is an unsatisfactory result.

        Key words: Chiari malformation, syringomyelia, decompression of craniocervical junction, neocisterna magna, dural plasty