• An 11-year-old male neutered Portuguese Water Dog presented for ataxia and abnormal mentation.
• The owner reports that the patient had seemed confused and staring at walls for a week prior to presentation. The patient also had trouble navigating corners and had eliminated in the house several times in the last few days.
• On presentation, the patient had normal mentation and appeared visual OU. The patient had markedly reduced menace response OS and normal OD, anisocoria with mydriasis OS, direct PLR absent OS with normal consensual response OD, normal direct PLR OD with absent consensual response OS. He had mild to moderate pelvic limb general proprioceptive ataxia. The remainder of the neurologic exam was unremarkable. A grade III/VI systolic cardiac murmur with PMI over left apex was auscultated. There was reduced range of motion and crepitus in both stifles and coxofemoral joints. The rest of the physical exam was unremarkable.
• Blood work was performed prior to MRI. A complete blood cell count showed a mild leukocytosis and stress leukogram. A chemistry panel displayed mild elevations to BUN, ALT, ALP as well as a mild hypokalemia.
• A left caudal pulmonary mass was found on survey thoracic radiographs prior to MRI. The owners were informed of the pulmonary mass and elected to proceed with the MRI.

MRI Report

MRI Findings:

• The brain was examined with standard MRI sequences including post contrast T1 weighted images in 3 planes.
• A seemingly crescent shaped (based on the dorsal T1 post-contrast) avidly contrast-enhancing lesion with well-defined and partially rounded borders is identified centered at the level of the interthalamic adhesion, eccentrically greater to the left of midline along the adjacent thalamus. It measures at most 8 x 8 x 9.5 mm. This lesion is hyperintense on T2/FLAIR without definitive perilesional edema or mass effect. A seemingly curvilinear shaped area of contrast enhancement measuring approximately 6.6 mm in length is identified at the junction of the left temporal/occipital lobe lateral to the left lateral ventricle. Multifocal, T2/FLAIR hyperintensities that do not display contrast enhancement are identified within the surrounding cerebrum supporting the presence of edema. These changes do not result in any significant mass effect
• .The pituitary gland is unremarkable. Overall meningeal/vascular enhancement within the brain is unremarkable. The ventricular system is unremarkable. The included portions of the cranial cervical spine are unremarkable. The cochlea of the inner ear, tympanic bulla, and external ear canals are unremarkable.
• Most appreciated on the dorsal plane post-contrast sequence, there is asymmetric accentuated contrast enhancement along portions of the left vascular tunic (i.e. for example ciliary body) and region of the choroid/retina. Overall the size of the globes are symmetric. Aqueous and vitreous humor signal is unremarkable and symmetric. No definitive abnormalities are identified along the extracalvarial portions of the optic nerve or optic chiasm. No significant abnormalities are identified along the remainder of the skull.

MRI Diagnosis:

• Intra-axial lesions at the level of the left thalamus and left temporal/occipital lobe junction with coexisting edema affiliated with the latter.
• Primary differentials include an inflammatory/infectious (including granulomatous) encephalitis followed by atypical manifestation of metastatic neoplasia. The left ocular changes are supportive of uveitis/chorioretinitis.

Additional diagnostics:

CSF Analysis:

Immediately following obtaining the MRI sequences, a CSF tap was performed and samples were sent to the reference laboratory for interpretation.

• The sample had elevated protein level of 35.5 mg/dL (0.0-35.0 mg/dL), and elevated nucleated cell count of 7 cells/uL (0-4 cells/uL). The cells are 59% unclassified cells, 29% small, mature lymphocytes, and 12% monocytoid cells.
• Unclassified cells are large (12 to 15 um) with round to oval to indented nuclei, lightly granular chromatin, possible nucleoli, and scant, deeply basophilic cytoplasm. No infectious agents are seen. There is a mild lymphocytic pleocytosis composed predominantly of large cells morphologically compatible with large lymphocytes.
  • Although it is possible this population of large cells represents a reactive population, cellular morphology and the preponderance of this population is highly suspicious for underlying large cell lymphoma.

Follow-up Radiographs:

The following day, the patient developed a wet cough with increased rate and effort. Three-view thoracic radiographs were obtained.

• Findings: The cardiac silhouette and pulmonary vasculature remain within normal limits. There is a solid, ~ 6 x 5 cm soft tissue mass within the axial aspect of the left caudal lung lobe. The margins of this lesion are well-defined on the lateral view. It summates with the apex of the cardiac silhouette on the ventrodorsal projection due to its location. There is a variable unstructured interstitial coalescing to alveolar pattern within both subsegments of the left cranial lung lobe, right middle and to a lesser degree right cranial lung lobe. On the current examination, there is also variability in the diameter of the gas column within the trachea being moderately narrowed throughout the mid cervical through cranial thoracic trachea to approximately the level of T4. No definitive abnormalities are identified in the region of the esophagus. No intrathoracic lymphadenopathy or pleural effusion is appreciated.
• Radiographic Diagnosis: Ventrally distributed pulmonary infiltrates and moderate narrowing of the gas column along the cervical and intrathoracic trachea. Aspiration pneumonia and tracheal wall edema/inflammation are prioritized given the appearance/distribution and history of recent general anesthesia. Left caudal lung lobe pulmonary mass. Primary consideration is primary pulmonary neoplasia such as a carcinoma.

Conclusion and Case Discussion

Following the diagnosis of aspiration pneumonia, the owners elected humane euthanasia.

CNS lymphoma is the third most common secondary intracranial tumor in dogs and accounted for only 4% of all primary intracranial tumors.^{1, 2} The mean age of dogs with CNS lymphoma was reported to be 7.4 years with Rottweilers being predisposed. Primary CNS lymphoma can involve the neuroparenchyma and/or the meninges. Secondary CNS lymphomas represent a metastatic process from a lymphoma outside the CNS, and are more common. The etiology is unknown in both animals and humans, except in cats in which FeLV is often involved and in immunocompromised humans in which the Epstein-Barr virus (EBV) plays a major role (EBV has not been associated with PCNSL in immunocompetent human patients).³ Previous studies have described MRI findings for CNS lymphoma typically as T2 isointense to hyperintense and FLAIR isointense compared to grey matter, strongly homogeneous contrast enhancing lesions with indistinct margins, and perilesional FLAIR hyperintensities as well as mass effect.⁴ These findings differ greatly from the images obtained in this case, which displayed lesions that were T2 and FLAIR hyperintense with well-defined margins and no evidence of FLAIR perilesional hyperintensities or mass effect, though it did show strongly homogeneous contrast enhancement. This case demonstrates the diversity of presentation for CNS lymphoma on MRI and how CNS lymphoma can mimic many other differential diagnoses. Unfortunately, histopathology was not obtained in this case to definitively determine the nature of the pulmonary mass. Secondary pulmonary lymphoma can present as a solitary mass in the context of multicentric or extranodal disease.⁵ Alternatively, a synchronous primary pulmonary neoplasm is a more common presentation.⁷

References

1. Snyder JM, Shofer FS, Van Winkle TJ, Massicotte C. Canine intracranial primary neoplasia: 173 cases (1986–2003). J Vet Intern Med 2006; 20: 669– 675.

2. Snyder JM, Lipitz L, Skorupski KA, Shofer FS, Van Winkle TJ. Secondary intracranial neoplasia in the dog: 177 cases (1986–2003). J Vet Intern Med 2008; 22: 172– 177.

3. Arbelo M, Espinosa de los Monteros A, Herraez P, et al. Primary central nervous system T-cell lymphoma in a common dolphin (Delphinus delphis). J Comp Path. 2014; 150:336-340.

4. Palus, V., Volk, H.A., Lamb, C.R., Targett, M.P. and Cherubini, G.B. (2012), MRI FEATURES OF CNS LYMPHOMA IN DOGS AND CATS. Veterinary Radiology & Ultrasound, 53: 44-49. https://doi.org/10.1111/j.1740-8261.2011.01872.x

5. Geyer, N.E., Reichle, J.K., Valdés-Martínez, A., Williams, J., Goggin, J.M., Leach, L., Hanson, J., Hill, S. and Axam, T. (2010), RADIOGRAPHIC APPEARANCE OF CONFIRMED PULMONARY LYMPHOMA IN CATS AND DOGS. Veterinary Radiology & Ultrasound, 51: 386-390. https://doi.org/10.1111/j.1740-8261.2010.01683.x