SMART syndrome

Last revised by Dr Rohit Sharma on 15 May 2022

SMART syndrome, an acronym for stroke-like migraine attacks after radiation therapy, is an uncommon delayed complication of cerebral radiation therapy. It is probably a more severe manifestation of peri-ictal pseudoprogression (PIPG)

SMART syndrome is encountered in individuals who have received therapeutic cerebral irradiation (>50 Gy), typically years later (6-30 years) 1,2,6. In most instances, patients have a history of seizures 6

The diagnosis of SMART syndrome is essentially one of exclusion and can only be entertained in the correct clinical setting. Various criteria have been proposed 2,8 although these are evolving. They can be generally summarized as follows:

  • patient: history of cranial irradiation (typically years ago) with no residual/recurrent tumor
  • clinical: prolonged (usually reversible) symptoms referrable to a unilateral cortical area that has been irradiated
  • imaging: prominent gyral enhancement (usually transient) within an area of previously irradiated brain

Patients usually present with seizures and subacute stroke-like episodes with symptoms such as hemiplegia, aphasia, and hemianopia 6. These episodes have been associated with headaches and are often preceded by a migraine-like aura 1,2.

The precise mechanism that underlies SMART syndrome is uncertain and biopsies obtained from some patients do not reveal specific abnormalities above and beyond those expected in previously irradiated brain 6

It is hypothesized that SMART syndrome represents an exacerbation of normal post-ictal phenomena due to prior radiotherapy 6

MRI is the modality of choice to investigate SMART syndrome. Importantly, imaging abnormalities do not precede or coincide with symptom onset; rather, it takes 2-7 days for imaging abnormalities to develop 6. As such, if imaging is performed early, a repeat scan is advisable a week later to have a better chance of identifying abnormalities.  

On initial imaging, a region of relatively minor low density with mass effect can be seen. Features of laminar necrosis in the involved territory, such as cortical calcifications, can be seen following the initial episode.

The hallmark of SMART syndrome is prominent gyral enhancement with mild mass effect cortical thickening (hyperintense in T2 and FLAIR) with or without diffusion restriction. It is usually unilateral and confined to the areas of the brain that underwent irradiation. 

  • T1:
    • initially low signal
    • hyperintense signal within the cortex can be seen if associated with cortical laminar necrosis on follow-up imaging
  • T2/FLAIR: hyperintense signal, often with cortical thickening
  • DWI/ADC: diffusion restriction is minor and variable, dominated by T2 shine through effects 6
  • SWI: foci of susceptibility artifacts may be seen, thought to be related to cavernous malformations induced by remote radiotherapy rather than SMART syndrome directly
  • T1C+ (Gd): prominent gyriform enhancement (cortical and leptomeningeal)

SMART syndrome was initially thought to be self-limiting with gradual and complete resolution over the course of several weeks; typically occurring within 2-5 weeks but can take up to 3 months 4,6.

However, incomplete clinical recovery is not uncommon (up to ~45% of subjects in one series 6). In a smaller proportion of patients (~27%) permanent imaging sequelae are also encountered consistent with cortical laminar necrosis, visible within a few weeks of presentation 6

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Cases and figures

  • Case 1
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  • Case 2
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  • Case 3
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