We are back from RSNA and it is time to post a new educational activity in our blog.  This presentation, by one of our previous neuroradiology fellows, addresses the typical and atypical findings and utility of DWI in the evaluation of brain abscesses.

Further questioning of patient disclosed that the symptoms had had a sudden onset 7 days earlier.  The diagnosis of subacute infarction of the right posterior inferior cerebellar artery territory was considered as the most likely cause of the findings.  The patient was followed and repeat MRI three months later demonstrated only malacia and atrophy in the location.

Llermitte-Duclos disease (a.k.a. dysplastic gangliocytoma of the cerebellum) is the CNS hallmark of Cowden syndrome.  It is probably a malformative hamartoma of the cerebellum seen nearly exclusively in this syndrome.  The typical lesion has a “corduroy” or “tiger striped” appearance, does not enhance after contrast, has restricted diffusion (presumably due to its high cellularity), and normal-to-increased perfusion. MRS shows low NAA, decreased Cho/Cr, elevated lactate and high myoinositol and at times the spectra may be near normal (see below).  PET shows increased FDG accumulation.  Thus to differentiate it from an infarct with similar appearance perfusion and PET studies are best when in doubt.  Additionally, contrast enhancement in Llermitte-Duclos is extremely rare.

Suggested readings:

Klish J, JUengling F, Spreer J, Koch D, et la. Llhermitte-Duclos disease: assessment with MR imaging, positron emission tomography, single photon emission CT, and MR spectroscopy. AJNR Am J Neuroradiol 2001; 22: 824-30

Moonis G, Ibrahim M, Melhem ER. Diffusion-weighted MRI in Llermitte-Duclos disease: report of two cases. Neuroradiology 2004; 46: 351-54

Awwad EE, Levy E, Martin DW, Merenda GO. Atypical MR appearance of Lhermitte-Duclos disease with contrast enhancement. AJNR Am J Neuroradiol 1995; 16: 1719-20

1.  I have  a sample with some ADC values obtained in 1,5 T and others obtained in 3T ( same b value). Can I use the ADC values for statistics or do you think that they cannot be compared?

2.  Are the ADC values obtained using a diffusion sequence  the same that the ADC values obtained in a DTI sequence with 12 directions?

Thank you in advance.

This patient had left central retinal artery occlusion and acute ischemic optic neuropathy. There is restricted diffusion in the anterior left optic nerve which is much more obvious than the mild perineural enhancement on coronal postcontrast images.