Subependymal Spread of Glioblastoma Multiforme in Positron Emission Tomography/Computed Tomography

Sir,

In a paper published recently aimed to compare the diagnostic reliability of (¹⁸F)-L-dihydroxyphenylalanine (¹⁸F FDOPA) versus magnetic resonance imaging (MRI) in primary brain tumors,[1] positron emission tomography/computed tomography (PET/CT) proved to be superior to MRI in evaluating recurrence and residual tumor tissue.[1] Here, we report a case of recurrent glioblastoma multiforme (GM) of the left frontal lobe. The patient was admitted to our center after a seizure episode in the right upper limb and a history of cognitive and memory impairment, apathy, and depression. The patient underwent surgical resection of the primary tumor and then underwent an ¹⁸F FDOPA PET/CT examination 2 months after surgery.

In Figure 1 (a, arrows), the axial PET/CT performed 15 min after the injection of 210 MBq of ¹⁸F FDOPA with a low-dose CT scan of the head for attenuation correction and reconstruction of PET images performed by means of ordered subset expectation maximization algorithm with four iterations and twenty subsets show an increased uptake of the radiotracer in two subependymal areas around the right lateral ventricle (arrows) which was evident as intense contrast enhancement on T1-weighted MR images (b and c, arrows). These findings have been confirmed in a subsequent MRI scan performed after 3 months, showing an increase in size of the subependymal findings [Figure 1]. In Figure 1a, the “*” highlights an area of ¹⁸F FDOPA uptake that is consistent with inflammatory process at the surgical site.[2] Informed consent was obtained from the patient.

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Figure 1 Multimodality imaging, (a) axial PET/CT image, (b,c) T1 weighed MR images, of glioblastoma multiforme showing subependymal spread as indicated by arrows)

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[¹⁸F] FDOPA PET/CT has been proposed for the study of primary brain tumors and a higher diagnostic accuracy of this imaging modality as compared to contrast-enhanced MRI, has been reported.[1] Multifocal lesions with subependymal or subarachnoid spread is a quiet rare condition representing approximately 1.2% of recurrence in GM and approximately 15% of the intracranial dissemination of GM in adults.[3] If one considers that subependymal and periventricular enhancement in MRI could be related to several benign conditions (periventricular vascular structures, arteriovenous malformations, collateral venous drainage, etc.),[4] this report highlights that ¹⁸F FDOPA PET could be used in addition to conventional imaging modalities for staging and detection of GM and its recurrence at this unusual site for its capability to discriminate between benign and pathological tissue.