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Michaela J. Beasley, Elizabeth C. Hiebert, Cody Alcott, Nicholas Jeffery, Brooklynn LaFoon-Jones, Jennifer M. Gambino
Background
Aberrant migration of Dirofilaria immitis (heartworm) into the central nervous system is rare but can result in severe neurologic disease. Previous reports have described its occurrence, but there is limited information on the computed tomographic (CT) and magnetic resonance imaging (MRI) characteristics of this condition. This study aimed to describe the clinical and imaging findings of four dogs diagnosed with verminous myelopathy due to D. immitis migration into the cervical subarachnoid space.
Methods
A retrospective case series was conducted by reviewing medical records from two veterinary institutions. Four toy breed dogs with MRI-confirmed cervical subarachnoid D. immitis migration were included. Clinical data, diagnostic imaging (MRI and CT when available), and surgical or necropsy findings were analyzed. Imaging findings were assessed for lesion characteristics, spinal cord compression, and nematode visualization.
Results
All dogs were heartworm antigen-positive and presented with neurological signs ranging from cervical hyperesthesia to tetraparesis. MRI revealed a single, large, fusiform, intradural-extramedullary mass with mixed T2-weighted and T1-weighted signal intensity, compressing the spinal cord. Nematodes appeared as serpentine or circular hypointense structures within the subarachnoid space. CT, performed in two dogs, demonstrated mildly enhancing intradural-extramedullary lesions. Surgical removal was performed in three dogs, with live immature D. immitis worms extracted, leading to full neurological recovery. One dog was euthanized, and necropsy confirmed an adult heartworm at C2.
Limitations
The study included only four cases, limiting generalizability. Variability in CT protocols and the absence of standardized MRI criteria for nematode detection may have influenced findings. The retrospective nature of the study also restricted control over data collection and imaging techniques.
Conclusions
Cervical spinal subarachnoid D. immitis migration should be considered in dogs with compatible clinical and imaging findings, especially in endemic regions. MRI is the preferred diagnostic tool, as CT findings were inconsistent. Surgical removal resulted in complete resolution of clinical signs in three cases, indicating that early detection and intervention may lead to a favorable prognosis.
Sagittal pre- (A-C) and postcontrast (D and E) MRI of patient 2 (3T, dorsal recumbency). A, FRFSE myelogram-like sequence, 1.2 mm slice thickness The loss of normal CSF signal hyperintensity at C2-4 is due to the space occupying nature of the lesion (arrowheads). The well-delineated, linear nematode is void of signal (arrow). (B) T2-W image, 2 mm slice thickness. T2-W hyperintensity predominates due to subdural edema and inflammation surrounding the hypointense nematode (arrow). C, T1-W FLAIR image, 2 mm slice thickness. The lesion is iso- to hypointense (compared to white matter). There is no evidence of early to late subacute hemorrhage. The nematode is persistently hypointense (arrow). Fat saturated postcontrast T1-W FLAIR FS+C image (D) 2 mm slice thickness; and transverse T1-W FSPGR FS+C image (E) 2.4 mm slice thickness. Avid dural enhancement surrounds the nonenhancing nematode (arrow, D). In cross section, the coiled, non-enhancing, compressive nematode has a pinpoint intradural architecture (small arrows, E). These image features were consistently seen in all four dogs and were interpreted to be representative of the lesion
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