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Neuroradiology Case of
the Week
Case 126
Loris F. Cedeno, MD, Jeevak Almast, MD,
and Per-Lennart Westesson, MD, PhD, DDS
Clinical
Presentation: A
33-year-old female who is 28 weeks pregnant presented with a possible fetal cerebellar abnormality on prenatal ultrasound.
Radiological
Findings: The left cerebellar hemisphere is not visualized. The fourth ventricle appears to communicate with the subarachnoid space. The right cerebellar hemisphere is normal in appearance. The posterior fossa is not enlarged. The tentorium cerebelli is normal in location. The pons is normal in appearance and the vermis is present. However a true coronal view was not obtained due to fetal movement. (Figs. 1-5).
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Figure 5 |
Diagnosis:
Cerebellar dysplasia/cerebellar atrophy/hypoplasia of unknown cause
Discussion: Cerebellar dysplasias are a heterogeneous group of entities including cerebellar ageneses, hypoplasia, and even early cerebellar atrophy. Malformations can affect the vermis or the hemispheres (often bilaterally) as well as possibly the brainstem. They are very different entities sometimes classified as the conglomerate of Dandy Walker variants in the literature.
The cerebellum develops from centers in the rhombic lip of the metencephalon. These grow into the cerebellar hemispheres and fuse centrally to form the vermis. Fusion starts anterosuperiorly with the posteroinferior part of the vermis fuses last. There are several genes and certain molecules such as netrins that play a role in cerebellar development. Abnormalities associated with these elements can be diffuse and/or severe. Hypoplastic cerebella can be considered to result from reduction or premature cessation of cell production or cell migration or of excessive apoptosis in the developing cerebellum. Dysplastic cerebella are considered to be the result of abnormal cell migration and cortical organization, with resultant distortions of folia and fissures.
Unilateral cerebellar aplasia is one of the least frequent malformations of the cerebellum. When associated with other cerebral anomalies, it can be secondary to genetic causes. It can also occur as part of crossed cerebellar diaschisis which is defined as functional impairment and cerebellar atrophy, remote from and contralateral to a causative supratentorial lesion. In addition, unilateral or focal cerebellar atrophy can be due to a localized hypoxic-ischemic lesion, early vascular insult or infarct. This was felt to be the most likely cause in our patient as no other parenchymal abnormalities were appreciated.
References:
- Akgul E, Soyupak S, Bicakci K. Unilateral cerebellar aplasia, (2002, May 14). [Online] [http://www.eurorad.org/case.cfm?UID=1639] Luxembourg, Euromultimedia.
- Patel S, Barkovich AJ. Analysis and classification of cerebellar malformations. AJNR Am J Neuroradiol. 2002 Aug;23(7):1074-87. [Medline]
- Garel C. MRI of the Fetal Brain, Springer-Verlag, 2004, Chapter 12.
- Kozic D, Kostic VS. Crossed cerebrocerebellar atrophy. Arch Neurol. 2001 Nov;58(11):1929-30. [Medline]
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