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Findings: A prominence of the 4th ventricle was noted, disproportionate to the size of the lateral and 3rd ventricles. Multiple remote infarcts in the right temporal lobe, left cerebellum, lacunar infarct in the brainstem and small vessel ischemic changes in the subcortical white matter tracks. Diffuse cerebellar atrophy was also noted.
Diagnosis: Isolated dilation of the fourth ventricle.
Discussion: The differential diagnoses of an isolated dilation of the fourth ventricle include — cerebellar atrophy, arachnoid cysts, "Isolated fourth ventricle" (IFV) and "Disproportionately large, communicating fourth ventricle" (DLCFV). Intraventricular arachnoid cysts are very rare, with only very few cases having been reported in the literature, out of which only two cases have been reported presenting as a normal pressure hydrocephalus.
In this patient, with no prior history of neurosurgery, CNS infection or tumor, the diagnosis of IFV and DLCFV are effectively ruled out. The CT does not show the presence of a cyst, moreover the likelihood of a normal pressure hydrocephalus is very low. The likely diagnosis in this patient is cerebellar atrophy, as may be seen with alcohol use, with the atrophy mostly in the periventricular areas. The causes for cerebellar degeneration are — age related in the dorsomedial vermian lobules; developmental as in infantile autism, fragile X syndrome, Rett and Down’s syndromes; hereditary as in olivoponto-cerebellar atrophy (OPCA), cerebellar cortical degeneration and spinocerebellar degeneration (Friedreich’s ataxia); and acquired in ethanol abuse, paraneoplastic syndromes (subacute cortical cerebellar degeneration, and opsoclonus-myoclonus).
A diagnosis of IFV is made when there is enlargement of the fourth ventricle with obstruction of both the inlet (aqueduct of Sylvius) and the outlet (foramina of Lushka and Magendie) to the ventricle. The condition is almost always secondary to shunting of the lateral ventricles. Four cases of IFV following neurocysticercosis have been reported. DLCFV is similar to IFV except here the aqueduct is patent, which can be demonstrated by Conray or Metrizamide ventriculography. Here too, the condition is often post-shunting, but can occur after other CNS/spinal surgery, meningitis or after subarachnoid hemorrhage. Both these conditions present with a similar imaging appearance — dilation of the fourth ventricle, compression and distortion of the brain stem and upward tentorial herniation. The symptoms are that of cerebellar and lower cranial nerve dysfunction, with the cerebellar triad of nystagmus, Parinaud’s sign and truncal ataxia being characteristic.
References:
Scotti G, et al. "The isolated fourth ventricle in children: CT and clinical
review of 16 cases". AJR Am J Roentgenol, 135(6): 1233-1238, 1980.
Matsumoto M, et al. "Disproportionately large communicating fourth
ventricle — report of 2 cases". No Shinkei Geka, 11(11): 1185-1190, 1983.
Kojima N, et al. "Clinical evaluation of isolated fourth ventricle".
No To Shinkei, 40(7): 679-687, 1988.
Shose, et al. "Disproportionately large, communicating fourth ventricle.
Case report." Neurol Med Chir (Tokyo), 31(13): 1003-1007, 1991.
Harrison’s Principles of Internal Medicine, 13th edition, p1223.
Kuroki T, et al. "Disproportionately large, communicating fourth ventricle;
report of 4 cases". No Shinkei Geka, 20(6): 707-711, 1992.
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