Images below require Macromedia's Flash Player to view

Neuroradiology Case of the Week

Case 167

Sudhir Kathuria, MD, Xiang Liu, MD, PhD, Sven Ekholm, MD, PhD,
and Per-Lennart Westesson, MD, PhD, DDS

Clinical Presentation: A 50-year-old patient with history of old infarction with bilateral hyper-reflexia.

Radiological Findings:

Diagnosis: Wallerian degeneration

Discussion: Wallerian degeneration is the process of progressive demyelination and disintegration of the distal axonal segment following the damage to the neuron. Wallerian degeneration may result from cerebral infarction, hemorrhage, trauma, necrosis, and focal demyelination. Magnetic resonance imaging (MRI) provides excellent visualization of intergraded (Wallerian) degeneration in brain.

     Wallerian degeneration develops through various stages.

• First stage is characterized by the physical disintegration of the axons and myelin sheaths with little chemical changes.
• Second stage is characterized by rapid destruction of the myelin fragments observed in first stage. In humans, within three months most of myelin breaks down into simple lipids and neutral fats.
• In the Third stage, the myelin sheath has almost disappeared, and gliosis occupies the area of the degenerated axons and myelin sheaths.
• The Fourth stage is characterized by volume loss following atrophy of the white matter tracts.

     These histologic and metabolic changes provide specific findings at MR imaging. In stage 1 that lasts for first 4 week, usually we don’t see any signal abnormality on conventional MR. However, DWI has shown increased signal in cerebral peduncles as early as 3 days after stroke showing early stages of wallerian degeneration but only in about 20% of cases. Some studies have shown that Diffusion tensor imaging (DTI) is able to show this abnormality even earlier than DWI and with higher sensitivity. In stage 2 that is about 4-14 weeks after stroke, the tissue becomes more hydrophobic and results in hypointense signal intensity in T2-weighted and Proton density images. Stage 3 results from subsequent myelin lipid breakdown, gliosis, and tissue becomes hydrophilic that gives hyperintense signal on T2-weighted and FLAIR images. After several years, in stage 4 or end stage, we see volume loss from atrophy that in brain stem is seen as unilateral shrinkage following Wallerian degeneration of the corticospinal tract.

References:

1. De Simone T, Regna-Gladin C, Carriero MR, Farina L, Savoiardo M. Wallerian degeneration of the pontocerebellar fibers. AJNR Am J Neuroradiol. 2005 May;26(5):1062-5. [Medline]
2. Igarashi H, Katayama Y, Tsuganezawa T, Yamamuro M, Terashi A, Owan C. Three-dimensional anisotropy contrast (3DAC) magnetic resonance imaging of the human brain: application to assess Wallerian degeneration. Intern Med. 1998 Aug;37(8):662-8. [Medline]
3. Castillo M, Mukherji SK. Early abnormalities related to postinfarction Wallerian degeneration: evaluation with MR diffusion-weighted imaging. J Comput Assist Tomogr. 1999 Nov-Dec;23(6):1004-7. [Medline]
4. Kuhn MJ, Johnson KA, Davis KR. Wallerian degeneration: evaluation with MR imaging. Radiology. 1988 Jul;168(1):199-202. [Medline]
5. Inoue Y, Matsumura Y, Fukuda T, Nemoto Y, Shirahata N, et al. MR imaging of Wallerian degeneration in the brainstem: temporal relationships. AJNR Am J Neuroradiol. 1990 Sep-Oct;11(5):897-902. [Medline]