Could you spot an ependymoma?

VRU 2024

John F Griffin IV, William S Stevenson, Nathan C Nelson, Annie V Chen, Silke Hecht, Brian F Porter, C Elizabeth Boudreau, Swan Specchi, Marco Bernardini, Wilfried Mai

Background
Ependymomas are rare neoplasms in dogs, originating from the ependymal cells lining the ventricular system and central canal of the spinal cord. Limited descriptions of their magnetic resonance imaging (MRI) features exist. This study aims to detail the MRI characteristics of canine ependymomas, including intracranial and spinal cord lesions, to aid in differential diagnosis.

Methods
A multicenter, retrospective case series analyzed MRI scans of six dogs with histopathologically confirmed ependymomas (three intracranial and three spinal cord). MRI sequences included T1-weighted (T1W), T2-weighted (T2W), and contrast-enhanced images. Imaging features were independently evaluated by three veterinary radiologists, with consensus achieved for discrepancies.

Results
Intracranial Ependymomas:
-Located in the forebrain with heterogeneous signal intensity on T1W and T2W images.
-All showed hyperintensity to normal-appearing gray matter (NAGM) on T2W images, heterogeneous contrast enhancement, and signs of transtentorial herniation.
-Two cases exhibited intralesional cyst-like structures, T2W hyperintense edema, and a midline shift.

Spinal Cord Ependymomas:
-Intramedullary lesions located in the cervical or thoracic spinal cord.
-Isointense to NAGM on T1W images, hyperintense on T2W images, and associated with perilesional T2W hyperintensity.
-Moderate, heterogeneous contrast enhancement was present in all cases, but no intralesional cysts were observed.
-One dog had drop metastases (leptomeningeal spread).

Limitations
Small sample size (six cases) limits the generalizability of findings. Additionally, variations in MRI equipment and technical parameters across institutions could affect imaging consistency. Lack of brain imaging in spinal cord cases precluded assessment for primary tumors or additional metastases.

Conclusions
MRI features of canine ependymomas include intraventricular or intra-axial forebrain and intramedullary spinal cord masses with variable contrast enhancement and T2W hyperintensity. Although imaging features overlap with other CNS tumors, specific characteristics like intralesional cysts or drop metastases may suggest ependymoma as a differential diagnosis. Histopathological confirmation remains essential for definitive diagnosis.

MRI of ependymoma in a 5-year-old Rottweiler (field strength = 3 tesla). There is a contrast-enhancing mass involving the third ventricle and thalamus (*). A, The white arrowhead denotes a small area of intralesional fluid accumulation. The small white arrows denote the T2W hyperintensity of the adjacent brain (presumed vasogenic edema). The small black arrow denotes the third ventricle, which is displaced and abnormally shaped. B, The black arrowhead denotes a small region of reduced signal intensity, thought to represent intralesional hemorrhage. B, There is a susceptibility artifact involving the dorsal aspect of the brain. This is attributed to the close proximity of the air-filled frontal sinuses. T2W, T2-weighted image; T2*W, T2*-weighted image; T1W, T1-weighted image; T1W+C, T1-weighted image made after gadolinium-based contrast medium administration.

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