What is the role of MRI in the workup of olivopontocerebellar atrophy (OPCA)?

Updated: Dec 17, 2018
  • Author: Sombat Muengtaweepongsa, MD, MSc; Chief Editor: Selim R Benbadis, MD  more...
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Answer

MRI is the imaging study of choice in patients with olivopontocerebellar atrophy (OPCA) because CT scanning does not provide adequate resolution of the pons and cerebellum. MRI typically shows (1) pancerebellar and brainstem atrophy, with flattening of the pons; (2) an enlarged fourth ventricle and cerebellopontine angle; and (3) demyelination of the transverse pontine fibers. This demyelination of the transverse pontine fibers is responsible for the "hot cross bun" sign in a T2 weighted scan, which is thought to be highly specific for multiple system atrophy. Putaminal hyposignal intensity with hypersignal intensity rim in a T2 weighted scan represents putaminal atrophy also suggestive of a diagnosis of multiple system atrophy. [116, 117]

Axial T2 brain shows hyperintensity signals within Axial T2 brain shows hyperintensity signals within pons ("hot cross bun" sign).

 

Axial T2 weighed shows putaminal hyposignal intens Axial T2 weighed shows putaminal hyposignal intensity with hypersinal intensity rim.

In the first year after the onset of cerebellar symptoms in patients with OPCA, MRIs may be normal; therefore, serial MRI examinations are necessary for detecting infratentorial atrophy.

Brain MRI is also useful in patients presenting with spinocerebellar syndromes to exclude the diagnoses of multiple sclerosis, cerebrovascular disease, and malignancy.

MRI also permits visualization of pontine atrophy, which distinguishes OPCA from other forms of genetic ataxias, and presentations of multiple system atrophy that do not yet heavily involve the pons. MRI findings in old patients with some late-onset genetic ataxias, such as spinocerebellar ataxia type 36 (SCA-36), may show similar pattern of OPCA. [118]

MR SPECT has been used in case reports and shows a decreased NAA/Cr ratio consistent with atrophy. The clinical use of this is not yet defined. [119]

Positron emission tomography (PET) scanning shows reduced metabolism in the brain stem and cerebellum. While this finding is of academic interest, PET scanning is not necessary for the diagnostic workup of a patient with OPCA, and the results do not distinguish subtypes of OPCA.


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