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January 2020, Volume 70, Issue 1

IMAGING CORNER

Radiation induced Wallerian degeneration of corticospinal tract in a case of brain tumour

Javaria Aleem  ( Shaukat Khanam Memorial Cancer Hospital, Lahore, Pakistan )
Hira Farooq  ( Shaukat Khanam Memorial Cancer Hospital, Lahore, Pakistan )
Imran Khalid Niazi  ( Shaukat Khanam Memorial Cancer Hospital, Lahore, Pakistan )

Wallerian degeneration is antegrade degeneration that occurs distal to point of injury. Here we present a case of a 50 years old man, diagnosed as Astrocytoma grade II and IDH muted right frontal lobe, underwent surgical debulking of tumour followed by radiotherapy. After 1 year of radiation he developed left sided body weakness. MRI was performed that revealed linear T2/FLAIR hyperintense signals extending from centrum semiovale along the posterior limb of internal capsule to the cerebral peduncle reaching upto the pons consistent with radiation induced Wallerian degeneration.



Discussion


Wallerian degeneration is cascade of catabolic biochemical events mediated by innate immune response to neuron injury. It is also called as orthograde or antegrade degeneration as this process is directed away from cell body. It is named after the English neurophysiologist Augustus Volney Waller (1816-1870), who described the process in 1850.1 The insult to neuron can be due to various etiologies like brain infarction, haemorrhage, necrosis, demyelination, trauma, tumour, radiation or chemical. This catabolic process occurs in four steps and is mediated by invasion of series of macrophages, cytokines and activated Schwann cells. It is usually classified into four stages. The first stage involves degeneration of the axons and myelin sheaths with recruitment of macrophages and release of tumour necrosis factors and interleukins (0-4weeks). In the second stage there is rapid destruction of degenerated myelin protein fragments while lipids remain intact (4-14 weeks). Third, myelin lipid degeneration results in gliosis (>14 weeks). In the end stage there is atrophy of the white matter tracts (occurs in months to years). The small nerve fibers have capability to regenerate at severed ends and joins proximal end.1 Radiology has a key role in early detection and prevention of progression. On CT scan it appears as hypodensity along corticospinal tract pathway. MRI is important in early diagnosis, evaluating patholophysiological and chemical changes. On MRIT2W images show hypointense band in initial 10-14 days due to increase lipid content of myelin sheath and after 4 weeks signals turn to hyperintense. 2 In our case MRI FLAIR images demonstrated linear hyperintense band along path of right corticospinal tract extending from internal capsule to brain stem. This represents chronic nature and was induced by radiation to right frontal lobe tumour. The purpose of this case is to highlight the fact that this is one of the causes in deterioration of patient's condition in post therapy state. This should be considered while evaluating worsening patient symptoms with brain tumour in addition to tumour extension or therapy complications.


References


1. Kuhn MJ, Mikulis DJ, Ayoub DM, Kosofsky BE, Davis KR, Taveras JM. Wallerian degeneration after cerebral infarction: evaluation with sequenti al MR imaging. Radiolog y. 19 89 ;17 2:179 -82.

2. Puig J, Pedraza S, Blasco G, Daunis-I-Estadella J, Prats A, Prados F, et al. Wallerian Degeneration in the Corticospinal Tract Evaluated by Diffusion Tensor Imaging Correlates with Motor Deficit 30 Days after Middle CerebralArtery Ischemic Stroke. AJNR Am J Neuroradiol. 2010 ;31:1324-30.

Journal of the Pakistan Medical Association has agreed to receive and publish manuscripts in accordance with the principles of the following committees: