Case Report: 18F-Fluoro-L-Phenylalanine Positron Emission Tomography Findings and Immunoreactivity for L-Type Amino Acid Transporter 1 in a Dog With Meningioma

Abstract

A 12-year-old intact female Miniature Pinscher dog weighing 5.4 kg presented with a history of seizures. On neurological examination, postural reactions were decreased in the left-sided limbs, and menace responses were bilaterally absent. Magnetic resonance imaging (MRI) of the brain was performed, and a solitary amorphous mass (2.7 × 1.9 × 2.2 cm) was observed on the right side of the frontal lobe. Based on the signalment, clinical signs, and MRI findings, a brain tumor was tentatively diagnosed, and meningioma was suspected. The dog was treated with hydroxyurea, prednisolone, and other antiepileptic drugs. One week after the treatment began, postural reactions returned to normal, and the menace response improved. At 119 days after treatment, 18F-fluoro-L-phenylalanine (18F-FDOPA) positron emission tomography (PET) was performed. Marked 18F-FDOPA uptake was observed in the lesion. The mean and maximal standardized uptake values of the lesion were 2.61 and 3.72, respectively, and the tumor-to-normal tissue ratio was 1.95. At 355 days after the initial treatment, a second MRI scan was performed and the tumor size had increased to 3.5 × 2.8 × 2.9 cm. The dog died 443 days after the initial treatment and was definitively diagnosed with grade 1 meningioma by histopathological examination. Immunohistochemical staining for Ki67 and L-type amino acid transporter 1 was positive and negative for p53, respectively. The labeling index of Ki67 was 2.4%. This is the first case to demonstrate 18F-FDOPA PET findings in a clinical case of a dog histologically diagnosed with a meningioma.

Keywords: 18F-FDOPA; L-type amino acid transporter 1; brain tumor; canine; meningioma; positron emission tomography.

Figure 1

Findings from the first and second magnetic resonance (MRI) imaging of a dog with meningioma. Transverse T2-weighted (A,E), fluid-attenuated inversion recovery (B,F), and post-contrast (C,G) images at the optic chiasm level and sagittal T2-weighted images (D,H). The first MRI scan was performed before chemotherapy. A solitary amorphous mass (2.7 × 1.9 × 2.2 cm) can be observed in the right frontal lobe. The tumor lesion (arrows) shows hyperintensity on T2-weighted (A,D) and fluid-attenuated inversion recovery (B) images. Post-contrast (C) image shows uniformly remarkable enhancement (arrowhead). Second MRI was obtained 355 days after initial chemotherapy (E–H). A more severe midline shift compared with the findings of the first MRI scan can be observed and the size of the tumor increased to 3.5 × 2.8 × 2.9 cm.

Figure 2

18F-fluorodopa (18F-FDOPA) positron emission tomography (PET)/computed tomography (CT) findings in a dog with meningioma. PET/CT scan was performed 119 days after initial chemotherapy. (A) On 18F-FDOPA PET image, increased 18F-FDOPA uptake is shown with a black color, while low uptake is shown with a white color. 18F-FDOPA uptake was remarkable in the lesion (arrows). (B) On PET/CT fusion image, increased 18F-FDOPA uptake appeared to be yellow, while low uptake appeared black to red. (C) A contrast-enhanced CT image shows an intense enhancement of the mass. (D) Bone window CT after contrast medium injection (window width of 2,000 Hounsfield units, window level of 500 Hounsfield units) revealed cranial bone lysis around the tumor (arrowhead).

Figure 3

Histopathology and immunohistochemical evaluation of a meningioma in a dog. (A) Normal brain tissue was compressed by an encapsulated neoplastic mass (asterisk). Hematoxylin and eosin; ×6 magnification; bar = 5 mm. (B) Syncytial growth of round to oval meningothelial cells consisting solid sheet and meningeal whorls (arrow). Nuclei contain a clear space with prominent nucleoli (arrowhead). Hematoxylin and eosin; ×200 magnification; bar = 100 μm. (C) A Ki67 positive cell (arrowhead) can be observed. Hematoxylin counterstain; ×400 magnification; bar = 50 μm. (D) L-type amino acid transporter 1 stain showing strongly diffuse positive staining. Hematoxylin counterstain; ×100 magnification; bar = 200 μm.