PET-CT in brain disorders: The South African context

Abstract

Positron emission tomography combined with X-ray computed tomography (PET-CT) has an established role in the management of brain disorders, but may be underutilised in South Africa. Possible barriers to access include the limited number of PET-CT facilities and the lack of contemporary guidelines for the use of brain PET-CT in South Africa. The current review aims to highlight the evidence-based usage of brain Positron emission tomography (PET) in dementia, movement disorders, brain tumours, epilepsy, neuropsychiatric lupus, immune-mediated encephalitides, and brain infections. While being areas of research, there is currently no clinical role for the use of PET-CT in traumatic brain injury or in psychiatric or neurodevelopmental disorders. Strategies to expand the appropriate use of PET-CT in brain disorders are discussed in this article.

Keywords: F-18 fluoro-dihydroxyphenylalanine; F-18 fluorodeoxyglucose; Parkinson’s disease; brain; brain tumour; dementia; positron emission tomography.

FIGURE 1

Fluorine-18 FDG PET scans in dementia. Maximum intensity projections of the PET scan (in the right lateral position) are shown on the top row (individually scaled for comparability). Corresponding statistical images (reductions compared to a normal database) are shown in the bottom row.

FIGURE 2

Example of a single-subject statistical analysis (decreases) for a FDG PET scan of a patient with dementia with Lewy Bodies. The top row represents surface projections of both brain hemispheres from different angles. Subsequent rows represent negative deviations from the normal database mean (z-score) for all brain regions, normalised to global counts (GLB), thalamus (THL), cerebellum (CBL), and pons (PNS). Similar outputs are generated for statistical increases (not shown). In this example, reduced metabolism in bilateral parietal occipital vortices is evident. Such analyses are highly recommended to support the interpretation of brain PETs.

FIGURE 3

Fluorine-18 FDOPA PET scans in five patients with movement disorders demonstrating absence of dopaminergic deficit (a) in a patient with essential tremor, and progressive stages of dopaminergic deficit (b – e) in patients with neurodegenerative disorders of the striatum.

FIGURE 4

Fluorine-18 FDOPA (a) and FDG (b) PET scans in a patient with a movement disorder. The FDOPA PET convincingly demonstrates dopaminergic loss in bilateral putamina, while the FDG study demonstrates normal metabolism. These features are consistent with a diagnosis of idiopathic Parkinson’s disease.

FIGURE 5

Interictal FDG PET scan in a patient with intractable temporal lobe epilepsy being worked up for epilepsy surgery. The scan demonstrates marked hypometabolism in the left temporal lobe, confirming lateralisation of the epileptogenic focus. The right panel demonstrates the PET maximum intensity projection; top row - PET orthogonal slices; bottom row - fused (PET-CT) orthogonal slices.

FIGURE 6

Fluorine-18 FDG (a) and FDOPA (b) PET-CT (fusion) and PET images of a patient with suspected recurrence of a low-grade glioma. The FDG PET-CT study was normal, while FDOPA PET-CT (preferred) demonstrates clear recurrence in the right putamen. This recurrent lesion was initially missed on MRI.

FIGURE 7

Fluorine-18 FDG PET (maximum intensity projection) in a patient known with systemic lupus erythematosus who presented with new-onset of choreoathetoid movements. Intense, symmetrical uptake in the striatal nuclei is consistent with a known neurological manifestation of systemic lupus erythematosus. MRI in this case reported non-specific features of microangiopathy.