Initial CT finding
Martínez-Segura, Ana Belén (M.D.); Felices-Farias, José Manuel (M.D.); San-Leandro-Pardo, David (M.D.); Vázquez-Sáez, Victoria (M.D., Ph.D.); Bañón-García, Inmaculada (M.D.)Patient
37 years, male
A 37-year-old male patient arrived at the emergency room due to first episode of left facial paralysis and a subsequent generalized tonic-clonic seizure without sphincters relaxation. He remained in a post-critical state of drowsiness for a few minutes and recovered asymptomatic. The neurological examination revealed no abnormalities.
An unenhanced head Computed Tomography (CT) (Fig. 1) was performed, which showed a cortico-subcortical hypoattenuating area in the right frontal lobe, suggested of space-occupying lesion. To complete the examination, the patient underwent a brain Magnetic Resonance Image (MRI) (Fig. 2 and 3). It showed an intra-axial mass, measuring 2.8 x 3.1 x 2.7 cm, hypointense on T1-weighted image (WI), hyperintense on T2WI, with hemosiderin foci and hypointense core with hyperintense periphery on fluid-attenuated inversion recovery (FLAIR) sequence (mismatch sign). It had no restricted diffusion, no elevated perfusion and showed a nodular area of enhancement. Single-voxel MRI spectroscopy revealed reduced N-acetyl aspartate (NAA) and elevated choline (Cho), myoinositol, lipids and lactate. These findings were compatible with low-grade glial tumour, oligodendroglioma as the first diagnostic option. The patient underwent tumour resection. The histopathological analysis confirmed an anaplastic astrocytoma with isocitrate dehydrogenase (IDH) mutation and no 1p/19q co-deletion, World Health Organization (WHO) grade III.
Anaplastic astrocytoma (AA) consists in a malignant primary brain tumour . The clinical presentation includes focal neurologic symptoms depending on localization and generalized symptoms like headache, seizures, personality changes and cognitive dysfunction.
According to the 2016 WHO Classification of Tumours of the Central Nervous System (which integrated molecular markers in addition to histological features), AA corresponds with IDH-mutant and 1p/19q intact glioma . The IDH mutation and no 1p/19q co-deletion status can be predicted by conventional and advanced MRI .
MRI with gadolinium contrast is the imaging test of election for diagnosis and management . AA involves the white matter and causes expansion of the surrounding cortex. On conventional MRI, the T2-FLAIR mismatch sign is an easily detectable imaging finding that has been studied and validated recently [3–6]. It seems to play a relevant role in making preoperative diagnosis and treatment planning [7,8].
The T2-FLAIR mismatch sign is defined by a homogenously hyperintense signal on T2WI and a central hypointensity with peripheral hyperintensity on FLAIR . It represents a radiogenomic biomarker considered highly specific for IDH-mutant and 1p/19q non-co-deleted gliomas (astrocytomas), though with a low sensibility . This sign may reflect microcystic changes in IDH-mutant astrocytomas . False positives are uncommon in adults, due to oligodendroglioma (IDH-mutant and 1p/19q co-deleted glioma), compared to pediatric patients , as dysembryoplasticneuroepithelial tumour might also show similar findings on MRI, thus decreasing the specificity of the mismatch sign .
This sign is usually accompanied by hypodensity on CT, hypointensity on T1WI, facilitated diffusion, little or no contrast enhancement and low relative cerebral blood volume (rCBV) . The detection of 2-hydroxyglutarate on gliomas by MR spectroscopy has not been implemented due to overlap by other metabolites presented in normal brain.
Although IDH-mutant, 1p/19q non-co-deleted astrocytomas affect younger patients and have intermediate prognosis [1,2,6], the T2-FLAIR mismatch sign is not associated with survival [5,6,12].
The treatment of AA consists of surgical resection with safe margins, followed by radiotherapy and chemotherapy .
Written informed patient consent for publication has been obtained.
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