Other / Other / MRI

SMART syndrome

Stroke-like neurological episodes with seizures occurring years (6-30 years) after cerebral radiation therapy (>50 Gy), typically in patients with prior history of brain irradiation and seizure disorder.

Key Images

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Look For First
  • Prominent unilateral gyral enhancement on T1 post-gadolinium within previously irradiated territory
  • Cortical thickening and T2/FLAIR hyperintensity in the affected gyri
  • Imaging findings appearing 2-7 days AFTER symptom onset (not concurrent)
Key Image Findings
  • T1 post-gadolinium shows prominent cortical and leptomeningeal gyral enhancement, typically unilateral and confined to irradiated brain regions
  • T2/FLAIR demonstrates hyperintense signal with cortical thickening in the affected territory, often with mild mass effect
  • DWI/ADC shows variable and minor diffusion restriction, predominantly reflecting T2 shine-through rather than true restricted diffusion
  • CT may show low-density changes with mass effect acutely, and laminar necrosis features (cortical calcifications) on follow-up
  • Perfusion imaging (PWI) demonstrates mild cerebral blood flow increase acutely, with variable cerebral blood volume elevation in acute phase normalizing during postictal phase
  • SWI may reveal foci of susceptibility artifacts reflecting cavernous malformations from remote radiotherapy rather than SMART itself
  • 18-FDG and 18-F amino acid PET-CT show cortical hypermetabolism during acute phase and hypometabolism during recovery phase
  • Imaging abnormalities typically persist for weeks, distinguishing from transient postictal changes, with permanent imaging sequelae (cortical injury, paramagnetic substrate) visible in ~27% of patients
Differential Diagnosis
  • Non-convulsive status epilepticus and repeated focal seizures: similar imaging and clinical features but SMART changes persist for weeks whereas post-ictal changes resolve quickly
  • Peri-ictal pseudoprogression (PIPG): occurs in tumor patients, shows less cortical enhancement and more leptomeningeal enhancement, and lacks prominent headache
  • Subacute cerebral infarction: follows defined vascular territory distribution unlike SMART's irradiation-based distribution
  • Posterior reversible encephalopathy syndrome (PRES): typically bilateral and multi-lobar without irradiation history
  • MELAS (mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes): typically multifocal and not confined to irradiated territories
  • Hemiplegic migraine: lacks the persistent imaging enhancement and thickening characteristic of SMART
Discussion

SMART syndrome is a delayed complication of cerebral radiation therapy representing either a severe manifestation of peri-ictal pseudoprogression or an exacerbation of normal postictal phenomena due to radiation-induced changes in irradiated brain

Clinical diagnosis requires three key elements: prior cranial irradiation (years earlier), acute stroke-like symptoms referable to a unilateral cortical area, and prominent gyral enhancement on MRI within previously irradiated brain

Timing is critical: imaging abnormalities do not appear simultaneously with symptom onset but develop over 2-7 days after symptom onset; early negative imaging should prompt repeat scanning after 1 week

Most patients experience self-limited resolution with complete recovery within 2-5 weeks (up to 3 months), but incomplete recovery occurs in ~45% and permanent imaging changes appear in ~27% of patients

Pathophysiology remains uncertain; biopsies typically do not reveal specific abnormalities beyond those expected from prior radiotherapy, suggesting functional rather than structural mechanism

Antiseizure medications and calcium channel blockers may help in patients without self-limited disease, though evidence is limited

Reporting Pearls

Describe the findings as "unilateral gyral enhancement with cortical thickening and T2/FLAIR hyperintensity confined to the irradiated territory, consistent with SMART syndrome in this patient with remote history of cerebral radiotherapy." Always note the timing relative to symptom onset and recommend follow-up imaging if initial scan was obtained early in the clinical course.

Pitfalls
  • Misinterpreting the imaging as tumor recurrence or progression—key distinguishing features are the unilateral gyral-cortical enhancement pattern, lack of mass effect, and absence of residual/recurrent tumor on prior imaging
  • Performing imaging too early in the clinical course and missing the diagnosis—imaging abnormalities take 2-7 days to develop, so early negative scans require follow-up imaging 1 week later
  • Confusing SMART with peri-ictal pseudoprogression (PIPG) or status epilepticus—SMART shows more prominent cortical enhancement and lasts for weeks, while PIPG and seizure-related changes resolve more quickly
  • Failing to consider SMART in the differential when encountering stroke-like symptoms with enhancement in a patient with remote history of brain radiotherapy, leading to unnecessary workup for ischemic stroke or tumor
Source: Reference source

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