Clinical and Pathological Findings in a Red-Tailed Boa Constrictor (Boa constrictor constrictor) with a Primary Neural Neoplasm within the Diencephalon and Mesencephalon
A 22-yr-old red-tailed boa constrictor (Boa constrictor constrictor) was evaluated for neurologic abnormalities, including cervical weakness and right-sided optical and thermal blindness. Previous diagnostic testing of this individual had ruled out inclusion body disease of boids as a cause of the neurologic signs. Magnetic resonance imaging (MRI) with the use of both a 7-T research unit and a 1.5-T clinical unit was performed, and confirmed the diagnosis of a large mass within the diencephalon and mesencephalon causing hydrocephalus and asymmetry of the lateral ventricles. Both MRI units provided diagnostic images. Based upon the lack of surgical or medical options for treatment, euthanasia was elected. Necropsy and histopathology confirmed the presence of an intracranial mass, with gross images closely mirroring those noted antemortem with MRI. The mass was likely to have an ependymal or astrocytic origin based on immunoreactivity of neoplastic cells to glial fibrillary acidic protein and caused complete compression and/or effacement of components of the diencephalon, including the thalamus and pineal gland, as well as the mesencephalon. This case illustrates the neurologic deficits, application of advanced MRI for neuroimaging, and immunohistological characteristics of an uncommon primary neural neoplasia in a snake.Abstract
Dorsal plane T2-weighted images from a 7-T MRI of a red-tailed boa constrictor. The rostrum of the snake is toward the upper part of the image, and the right side of the snake is on the left side of the image. The hyperintense fluid in the lateral ventricles (star) highlights the asymmetric dilation and extension into the olfactory lobes. The slightly hypointense mass is in the region of the tectum; susceptibility artifacts are indicative of hemorrhage and more visible in 1B (short arrows). The mass is thought to be causing compression and obstruction of the ventricular system.
Magnetic resonance imaging (MRI) from a red-tailed boa from two MRI units; sagittal (A) and transverse (B) T2-weighted images from a 7-T research MRI unit and sagittal (C) and transverse (D) T1-weighted postcontrast images from a 1.5-T clinical MRI unit. On sagittal views (A, C) the rostrum is towards the left of the image and dorsal is toward the top of the image. On transverse views (B, D) dorsal is towards the top of the image and the right side of the patient is on the left side of the image. The mass (*) effaces the tectum and compresses the medulla. There is zipper artifact on the right-hand side of B.
Gross examination of the brain of a red-tailed boa constrictor euthanized due to an intracranial mass. A. The prosencephalon (PRO) is diffusely congested and enlarged bilaterally compared to the rhomboencephalon. Note the prominent pineal gland (PIN). See brain drawing in Figure 4 for neuroanatomical landmarks. B. On formalin 10-day postfixation transverse sections, the mass (arrows) completely replaced the thalamus and PIN, displacing the surrounding cerebral hemispheres. On cross section the mass is smooth, mottled white to tan, and firm, with one area of softness consistent with intratumoral necrosis (NEC). Note that the tumor is adhered to the dura mater at the level of the pineal gland. The mass extends to the midbrain (image to the right).
Diagrammatic dorsal view of the brain of a red-tailed boa constrictor with an intracranial mass (in red) within the diencephalon and midbrain and displacing laterally the telencephalic structures (cerebrum and hippocampus [not shown]) and dorsally the mesencephalic tectum (colliculi). The red vertical lines on the diagram denote the brain levels at which transverse sections 1–3 depicted below were obtained: 1. The tumor has totally replaced the diencephalon and compresses the surrounding cerebral lobes. 2. The tumor obliterates the dorsal diencephalon, which includes the thalamus and epithalamus (pineal gland; arrow). Note the dark basophilia of the multilobulated tumor. 3. The tumor extends into the midbrain. Note the multifocal dystrophic mineralization (small dark purple random foci), which are present within areas of necrosis.
Histologic and immunophenotypical characteristics of the primary diencephalic tumor. (A) The tumor is composed of small lobules of neoplastic cells with scant cytoplasm and dark basophilic round to elongated nuclei that are separated by fine bundles of fibrovascular stroma (arrows). Hematoxylin and eosin stain. ×200. (B) The cytoplasm of neoplastic cells are strongly immunoreactive for glial fibrillary acidic protein (GFAP). Immunohistochemistry. ×200. (C) Most neoplastic cells immunoreact to GFAP. Immunohistochemistry. ×400. (D) Very few cells within the neoplasm have cytoplasmic immunoreactivity to S-100. Immunohistochemistry. ×400.
