1.5 Tesla Magnetic Resonance Imaging Features of Canine Intracranial Intra-axial Hematomas

Background
The study addresses the differentiation of solitary intra-axial hematomas from hemorrhagic neoplasms using MRI in dogs. Accurate distinction is crucial due to differing treatments and prognoses. MRI's ability to detect intracranial hemorrhage in dogs is well-established, but the specific features of hematomas are less documented compared to human medicine. This research aimed to describe the MRI features of canine intra-axial hematomas and compare these findings to the established progression of hemorrhages in humans.

Methods
This retrospective study analyzed MRI data from ten dogs diagnosed with intra-axial hematomas. Inclusion criteria included complete brain MRI studies, histopathological confirmation, or follow-up imaging/clinical resolution. MRI protocols varied across institutions, but all used 1.5 Tesla magnets. Observers evaluated lesion location, size, shape, signal intensity, contrast enhancement, perilesional edema, and mass effects.

Results
-Lesion Characteristics: All hematomas had two distinct regions—a hypointense peripheral border and a heterogeneous, predominantly hyperintense central region on T2W and gradient echo (GRE) images. Peripheral enhancement was noted in 6/10 cases, while no central enhancement was observed.

-Clinical Correlation: Hematomas localized primarily in the white matter of the forebrain, with the frontal lobe being most affected. Presenting signs included seizures, ataxia, and hemiparesis.

-Temporal Evolution: All lesions showed characteristics of 2–7 day-old hematomas, consistent with the early subacute phase in dogs. Follow-up MRIs in four cases demonstrated lesion resolution and absence of perilesional edema.

-Signal Patterns: The uniform, complete hypointense rim and central hyperintensity in the hematomas mirrored findings in benign human cases. Distinct dichotomy between the peripheral and central regions was noted.

Limitations
The study's small sample size and limited histopathological confirmation (2/10 cases) constrain its generalizability. Retrospective design and variation in MRI protocols may introduce bias. Additionally, the inability to assess chronic hematoma evolution due to limited follow-up imaging restricts comprehensive understanding.

Conclusions
Canine intra-axial hematomas exhibit MRI features similar to benign human hematomas, including a thin hypointense rim, central hyperintensity, and peripheral enhancement without central enhancement. Accurate differentiation from neoplastic lesions is critical, and follow-up imaging is recommended for ambiguous cases. The study provides foundational imaging characteristics for clinical decision-making but underscores the need for further prospective studies.

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