Case of the Month: May, 2012, Page 2

Answer: Mucopolysaccharidosis. Genetic testing confirmed the diagnosis of Hunter’s syndrome.

Imaging findings:

  • Axial T1 and T2 MRI of the brain: On T1 diffuse ovoid and lenticular areas of hypointensity in the white matter are present. These areas have high T2 signal similar to CSF. Not shown: There is no associated gliosis or enhancement. These findings are consistent with prominent Virchow-Robin spaces.
  • Sagittal T1 of the cervical spine and Sagittal T2 of lumbar spine: There is a pannusbetween the arch of C1 and the odontoid process that extends posteriorly. It is causing narrowing of the spinal canal. The lumbar vertebrae demonstrate anterior beaking and posterior scalloping.

Discussion:

  • Mucopolysaccharidosis is an inherited disorder of the lysosomal enzymes that break down mucopolysaccharides, also known as glycosaminoglycans (GAGs). GAGs are proteins that are bound to repeating chains of sugar and form a wide variety of compounds. Some well-known members of this group of molecules include heparin, which is vital in anticoagulation, and chondroitin which is found in joints, ligaments, tendons and cartilage. The ubiquity of these molecules means they build up in nearly all tissues. This produces clinical and radiological findings which at first may seem unrelated.
  • Virchow-Robin spaces are perivascular spaces normally filled with interstitial fluid. In Hunter’s syndrome, these spaces become distended with mucopolysaccharides. The pannus at C1-2 is also formed by deposition within the stabilizing ligaments of the atlanto-axial joint. This cervical spine is particularly important to monitor because of the potential for spinal canal compromise and atlanto-axial instability. However, all tendons and ligaments are susceptible to enlargement.
  • The deposition of mucopolysaccharides within the vertebrae creates characteristic “beaks” andscallops seen on MRI. Deposition in the calvarium results in macrocephaly, frontal bossing and coarse facies. Long tubular bones such as ribs and fingers are particularly susceptible to widening. The chest x-ray below is from the same patient and shows “oar ribs” which are ribs with normal thickness at the costovertebral joints but widen more distally. In this example, the lower ribs show this finding best.

(Click here for larger image.)


 

Prognosis and Treatment:

  • Unfortunately, the mucopolysaccharidoses are progressive diseases that often lead to significant morbidity and mortality. Radiologists should be cognizant of the wide variety of imaging manifestations.

References:
 

  • Heike E. Daldrup-Link, Charles A. Goodin. Essentials of Pediatric Radiology: A Multimodality Approach 2010, pg 244-248.
  • Kwee RM, Kwee TC. “RSNA Education Exhibits: Virchow-Robin Spaces at MR Imaging.” Radiographics July-August 2007 27:4 1071-1086; doi:10.1148/rg.274065722.
  • Statdx.com
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