World Arnold Chiari Malformation Association
Acquired vs. Congenital

1.  J Neurosurg 1995 Sep;83(3):556-558 Acquired Chiari I malformation and syringomyelia associated with bilateral chronic subdural hematoma. Case report.Morioka T, Shono T, Nishio S, Yoshida K, Hasuo K, Fukui M
Department of Neurosurgery, Kyushu University, Fukuoka, Japan.

The authors report a case of bilateral chronic subdural hematoma in a 25-year-old woman who had occipital and neck pain. Magnetic resonance imaging revealed progressive caudal descent of the cerebellar tonsils (acquired Chiari I malformation) and a large eccentric syrinx in the spinal cord from the C3-T7 levels. Spontaneous disappearance of the chronic subdural hematomas resulted in radiographic resolution of both lesions, as well as clinical improvement. Theories of syringomyelia formation, the relationship to acquired Chiari I malformation, and the implications of this case are discussed.


2.   J Neurosurg 1998 Feb;88(2):237-242
Acquired Chiari I malformation secondary to spontaneous spinal cerebrospinal
fluid leakage and chronic intracranial hypotension syndrome in seven cases.
Atkinson JL, Weinshenker BG, Miller GM, Piepgras DG, Mokri B

Department of Neurological Surgery, Mayo Clinic, Rochester, Minnesota 55905,

OBJECT: Spontaneous spinal cerebrospinal fluid (CSF) leakage with development of the intracranial hypotension syndrome and acquired Chiari I malformation due to lumbar spinal CSF diversion procedures have both been well described. However, concomitant presentation of both syndromes has rarely been reported. The object of this paper is to present data in seven cases in which both syndromes were present. Three illustrative cases are reported in detail. METHODS: The authors describe seven symptomatic cases of spontaneous spinal CSF leakage with chronic intracranial hypotension syndrome in which magnetic resonance (MR) images depicted dural enhancement, brain sagging, loss of CSF cisterns, and acquired Chiari I malformation. CONCLUSIONS: This subtype of intracranial hypotension syndrome probably results from chronic spinal drainage of CSF or high-flow CSF shunting and subsequent loss of brain buoyancy that results in brain settling and herniation of hindbrain structures through the foramen magnum. Of 35 cases of spontaneous spinal CSF leakage identified in the authors' practice over the last decade, MR imaging evidence of acquired Chiari I malformation has been shown in seven. Not to be confused with idiopathic Chiari I malformation, ideal therapy requires recognition of the syndrome and treatment directed to the site of the spinal CSF leak. PMID: 9452230, UI: 98112609

3.   Pediatr Neurosurg 1995;22(5):251-254
Acquired Chiari-I malformation and hydromyelia secondary to a giant   craniopharyngioma.

Lee M, Rezai AR, Wisoff JH
Division of Pediatric Neurosurgery, New York University Medical Center, NY 10016

     Hydromyelia, or hydrosyringomyelia is frequently associated with the Chiari I malformation of the cerebellar tonsils. Descent of the cerebellar tonsils is considered a congenital anomaly with a few reports of 'acquired' Chiari I malformation. We report a patient with a giant craniopharyngioma and hydrocephalus who at presentation had a concomitant Chiari I malformation and hydromyelia. The patient underwent gross total resection of the tumor and, with no further treatment, demonstrated spontaneous resolution of the Chiari I malformation and hydromyelia during the postoperative period. This suggests that the Chiari I malformation and the resulting hydromyelia were 'acquired', and were caused by an intracranial mass effect. This provides further evidence for an associative mechanism of cerebellar tonsillar descent and the development of hydromyelia. PMID: 7547457, UI: 96018158 

4.   "Acquired" Chiari I malformation. Case report.

Huang PP, Constantini S
Department of Neurosurgery, New York University Medical Center, New York.

Tonsillar descent of the cerebellum in Chiari I malformations is often considered a congenital defect. A patient is presented in whom magnetic resonance (MR) imaging revealed normally positioned cerebellar tonsils; however, 1 year later MR imaging was repeated for evaluation of gait abnormalities and showed descent of the cerebellar tonsils. This case illustrates worsening symptoms with progressive descent of the cerebellar tonsils and suggests that Chiari I malformations can evolve postnatally. Note: One would then reason that ACM is not necessarily congental i.e. is not always pre-existing:

5.   Acta Neurochir (Wien) 1998;140(5):417-27; discussion 427-8

The acquired Chiari malformation and syringomyelia following spinal CSF drainage: a study of incidence and management.

Johnston I, Jacobson E, Besser M
Department of Neurosurgery, New Children's Hospital, Australia.

Firstly, 14 patients are described who developed either an acquired Chiari malformation (ACM) alone (7 cases) or ACM and syringomyelia (7 cases) after lumbar subarachnoid space (SAS) shunting or in one case, epidural anaesthesia with SAS penetration. Four groups are considered: 3 cases with craniofacial dysostosis and communicating hydrocephalus (CH), 4 cases with CH alone, 3 cases with pseudotumour cerebri (PTC) and a miscellaneous group (4 cases). Initial treatment was varied: resiting the shunt to ventricle or cisterna magna [6], adding an H-V valve [1], syrinx shunting [4] and posterior fossa decompression [3]. Further treatment was required in 6 cases. Secondly, incidence was examined in 87 patients with PTC initially treated either by lumbar SAS shunting [70] or cisterna magna shunting [17]. In the first sub-group, 11 cases (15.7 per cent) developed an ACM, 3 symptomatic (as above) and eight asymptomatic with 1 case also having syringomyelia whereas 1 case occurred in the second group with a questionanably symptomatic ACM. While accurate for symptomatic lesions, these figures are tentative with respect to asymptomatic lesions due to inadequate pre-treatment radiology and detailed MR follow-up. The main conclusions are, first, that the incidence of symptomatic ACM and/or syringomyelia is not high enough to warrant abandoning SAS shunting; second that asymptomatic lesions need not necessarily be treated and third, that when treatment is required, shunt resiting is the first choice.

PMID: 9728240, UI: 98397486

A Case of a Temporary ACM/ Syrinx

28 yr old female with a car accident head injury- when the injury healed the ACM/syrinx almost disappeared

Source- W.C. Clivero and D.H. Dinh, Neurology, v. 30, #5, 758 (1992)


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