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UF Health University of Florida
Veterinary Diagnostic Imaging College of Veterinary Medicine
LA Radiology Overview

Case reveal

Findings:

BRAIN

  • Centered within the left aspect of the medulla oblongata, extending caudal to the pons to the level of the foramen magnum, there is a focal, ill-defined and non-contrast enhancing T2W and FLAIR hyperintense region (yellow circle).

ADDITINAL FINDINGS

  • Incompletely evaluated within the field of view, within the right conchofrontal sinus, there is a large amount of mildly heterogeneously contrast enhancing, iso to mildly T2W and FLAIR hyperintense and heterogeneously T1W hypointense material. On T2*W images, this material contains multiple, small, variable-shaped regions of signal void.
  • The right dorsal periocular soft tissues included in the field of view are moderately thickened and heterogeneous

Conclusions:

  • Locally extensive intra-axial brainstem lesion (left medulla oblongata) with likely involvement of the left facial motor nucleus and left caudal cerebellar peduncle in association with the reported neurological clinical signs. Differential diagnoses for this lesion include infectious or inflammatory encephalitis (e.g. equine protozoal myeloencephalitis), infiltrative neoplasia (e.g. lymphoma) or less likely infarction.
  • Incompletely evaluated moderate peribulbar soft tissue swelling with right conchofrontal effusion (e.g. hemorrhage), compatible with the reported facial trauma.

Follow-up:

CASE OUTCOME:

  • Following the MRI, cerebrospinal fluid was obtained for cytology and EPM testing. During recovery, the patient was unable to stand and was humanely euthanized.

CSF CYTOLOGY:

  •  Minimally increased microprotein, reflecting a biologic variation or due to impaired blood brain barrier permeability.

EPM TESTING:

  • Sarcocystic neuroma and Neospora hughesi serum:CSF ratio of 25 (a ratio less than 100 is highly diagnostic of clinical EPM)

GROSS NECROPSY:

  • Moderate focally extensive encephalomalacia (left brainstem- soft, poorly demarcated and light grey to light yellow region)
  • Moderate hemorrhage within the right conchofrontal sinus with right periorbital skin wound and subcutaneous edema 

HISTOPATHOLOGY:

  • Multifocally within the left cerebral cortex, left caudate nucleus, left thalamus and hyppocampus, midbrain and brainstem, there is a mild increase in glial cells number (gliosis), as well as hyperchromatic glial cells (glial satellitosis), with evidence of axonal degeneration. Similar findings are also identified within the medulla oblongata with small areas of acute hemorrhage within the neuronal parenchyma. 

FINAL ANATOMIC DIAGNOSIS: Moderate multifocal encephalitis, predominantly left-sided (cerebral cortex and brainstem), with secondary axonal degeneration, gliosis, and glial satellitosis

In correlation with the positive Sarcocystis neurona​ serology testing, equine protozoal encephalitis (EPM) was identified as the likely etiology for the histologically confirmed encephalitis.

A little bit more…

  • Previous studies evaluating the clinical progression of horses experimentally infected with EPM have also failed to recover the protozoa on post-mortem evaluation​.1,2 The absence of schizonts and merozoites in the histological sections may be in response to the prior therapy or due to sampling limitations. Alternatively, an immune-mediated pathogenesis has also been proposed as an etiology for the CNS inflammatory lesions described in Sarcocystis neurona ​positive horses.1 
  • The magnetic resonance imaging (MRI) appearance of the normal equine brain has previously been described using low field and high field MRI systems.3,4 However, there are no prior studies describing the MRI features of EPM in large population of horses. A prior report by Ferrell et al. identified brain lesions in two horses with positive CSF Western immunoblot testing for Sarcocystis neurona antibodies; however, histology was not available to confirm the etiology of the lesions​, which included a pituitary gland nodule containing protein-rich fluid and a fluid-cavitated cerebral mass.5 Another report identified multifocal areas of contrast enhancement in the cerebral cortex of a 2-month-old colt with suspected EPM, based on a positive Western immunoblot test and positive response to empirical treatment.6 In the current case, the brainstem lesion differed from prior MRI descriptions of possible EPM lesions, but corresponded to microscopic changes identified in histologically confirmed EPM cases.7 In addition, acute lesions have been described to contain multifocal regions of hemorrhage, similar to the current case. 7
  • The location and distribution of the brainstem inflammatory lesions correlated with the patient’s clinical signs and neurolocalization on physical examination. ​Sarcocystis neurona has been described to more commonly affect the brainstem, but can affect all regions of the CNS. 7 Clinical signs are variable depending on the location of lesions.7 – Increased recovery risks should be taken into consideration when anesthetizing a neurologic patient.8

References:

  1. Arencibia, Alberto, et al. “Magnetic resonance imaging of the normal equine brain.” Veterinary Radiology & Ultrasound 42.5 (2001): 405-408.
  2. Schmidt, Martin J., Carola Knemeyer, and Helmut Heinsen. “Neuroanatomy of the equine brain as revealed by high-field (3Tesla) magnetic-resonance-imaging.” PloS one 14.4 (2019).
  3. Sofaly, C. D., et al. “Experimental induction of equine protozoan myeloencephalitis (EPM) in the horse: Effect of Sarcocystis neurona sporocyst inoculation dose on the development of clinical neurologic disease.” Journal of Parasitology 88.6 (2002): 1164-1170.
  4. Fenger, Clara K., et al. “Experimental induction of equine protozoal myeloencephalitis in horses using Sarcocystis sp. sporocysts from the opossum (Didelphis virginiana).” Veterinary Parasitology 68.3 (1997): 199-213.
  5. Ferrell, Eric A., et al. “Magnetic resonance for evaluation of neurologic disease in 12 horses.” Veterinary Radiology & Ultrasound 43.6 (2002): 510-516.
  6. Gray, L. C., et al. “Suspected protozoal myeloencephalitis in a two-month-old colt.” Veterinary Record 149.9 (2001): 269-273.
  7. Dubey, J. P., et al. “A review of Sarcocystis neurona and equine protozoal myeloencephalitis (EPM).” Veterinary parasitology 95.2-4 (2001): 89-131.
  8. Hubbell, J. A. E. “Recovery from anaesthesia in horses.” Equine Veterinary Education 11.3 (1999): 160-167.