CT/MRI Society Case of the Month
March 2006
Sponsored by Eklin Medical Systems
Patient Identification Number: CTMRSOC1
Patient Surname Code: CTMRSOC
Patient First Name Code: HECHT
Accession Number: MAR06
Contributor: Silke Hecht
Contributor’s Affiliation: University of Tennessee College of Veterinary Medicine
Species: Canine
Breed: Toy Poodle
Age at exam: 3 years
Gender: Female spayed
Presenting signs and pertinent history: Presented to the neurology service with a 5 month history of progressive neck pain, increased vocalization and decreased neck movement. History of occasional seizures since 1 year of age (total 5-6 episodes/2 years)
Clinical/Neuro exam findings: Ataxia in all 4 limbs, tetraparesis, mild spinal hyperesthesia.
Relevant Laboratory data: Bloodwork unremarkable. CSF analysis unremarkable. Serology for toxoplasmosis, coccidiomycosis, neosporosis, cryptococcosis, blastomycosis, histoplasmosis and tick-borne diseases negative.
Primary clinical rule-out pre imaging: C1-C5 lesion; Anomalous/developmental (syringohydromyelia subsequent to Chiari type malformation) vs. inflammatory (infectious/non-infectious) vs. neoplastic vs. intervertebral disc disease.
Modality: MR
Manufacturer: Siemens Symphony
Model/Field Strength: 1.5 T
Sequences Acquired:
1) Brain: Transverse T1-w SE; transverse and sagittal T2-w SE ; transverse PD-w ; transverse FLAIR ; transverse T1-w SE post contrast
2) Cervical spine (study performed after brain MRI, i.e. all sequences post contrast): Sagittal and transverse T1-w SE; sagittal and transverse T2-w SE; sagittal and dorsal STIR; sagittal and dorsal HASTE (ultrafast heavily T2-w “myelogram” sequence)
CT/MR Findings:
1) Brain: On the sagittal T2-w images there is mild crowding of the caudal fossa with attenuation of the subarachnoid space and occipital impingement upon the cerebellum. There is thickening of the lining of both tympanic bullae.
2) Cervical spine: There is a fusiform mass within the spinal canal dorsal to the spinal cord extending from midbody C2 to the cranial aspect of C5. This mass is isointense to normal spinal cord on T2-w images, hypointense on STIR, and shows strong homogenous contrast enhancement. On the sagittal T1-w post contrast images there is the impression of a “dural tail” extending cranially and caudally along the dorsal aspect of the spinal cord. There is no evidence of a classic intradural-extramedullary sign on the HASTE images. The spinal cord adjacent to the mass shows ill-defined T2 hyperintensity, and the central canal is widened.
CT/MR Assessment:
1) Mass associated with the dorsal aspect of the spinal canal. Although there was no evidence of a classic “golf-tee” sign based on the HASTE images, an intradural-extramedullary mass (meningioma vs. lymphoma) was considered the most likely differential diagnosis based on the fusiform shape and the impression of a dural tail sign. An extradural or intramedullary lesion could not be excluded. Concurrent spinal cord edema and mild hydromyelia.
2) Mild crowding of the caudal fossa and occipital impingement upon the cerebellum, compatible with a Chiari-type malformation and likely incidental.
3) Thickening of the lining of both tympanic bullae, possibly secondary to previous or chronic otitis and likely incidental.
Post Imaging Management:
A dorsal laminectomy of C2-C4 was performed. The mass was determined to be intramedullary, with indistinguishable borders from the spinal cord. Complete removal therefore was not possible. The mass was debulked, and samples were submitted for cytology and histopathology.
Outcome:
The dog recovered slowly from anesthesia but was able to get up and stand on its own 2 days following surgery. Spinal hyperesthesia was decreased compared to the preoperative state. The dog showed continuous improvement and was discharged 5 days following surgery on prednisone, tramadol, clindamycin, omeprazol and diazepam. Impression cytology of the mass showed mild mixed (neutrophilic and lymphocytic) inflammation. Histopathology revealed marked, diffuse, necrotizing and pyogranulomatous myelitis, with complete replacement of spinal cord parenchyma by infiltrates of macrophages, neutrophils, plasma cells and lymphocytes. Special stains for bacteria and fungi were negative.
Final Diagnosis based on all diagnostic tests and outcome: Granulomatous meningoencephalitis (GME)
Comments:
GME is an idiopathic inflammatory disease of the CNS, characterized pathologically by accumulation of mononuclear cells in the parenchyma and meninges of brain and spinal cord. Young to middle-aged female dogs of small breeds (poodles, terriers) are predisposed. Clinical signs of either focal or multifocal CNS dysfunction are possible. In the disseminated form, lesions are distributed throughout the central nervous system with a predilection for the white matter of the cerebrum, cerebellum, brainstem and cervical spinal cord. The focal form occurs as a single granulomatous mass.
Most reported cases of GME have been diagnosed at necropsy. Antemortem diagnosis is based on signalment, history and results of diagnostic tests. Although most dogs show abnormalities on CSF analysis, the results are equivocal or normal in 10% of the patients.1,2
CT and MRI findings of GME of the brain have been reported.3,4 On CT, disseminated GME manifests as multiple contrast-enhancing lesions involving brain and meninges, possibly with concurrent edema and mass effect. Focal GME appears as an iso- or hyperdense mass. On MRI, focal GME has been described as iso- or hypointense mass on T1-w images and hyperintense mass on T2-w images with variable contrast enhancement.
Differentiating intradural from intradural-extramedullary lesions based on MRI can be difficult when an intramedullary mass borders the subarachnoid space or an intradural mass infiltrates the spinal cord.5 A myelogram might have been useful in identifying the location of this lesion.
References:
1. Dewey CW. Encephalopathies: Disorders of the Brain. In: Dewey CW, ed. A Practical Guide to Canine and Feline Neurology. Ames: Iowa State Press, 2003;99-178.
2. Thomas WB. Nonneoplastic disorders of the brain. Clinical Techniques in Small Animal Practice 1999;14:125-147.
3. Lobetti RG, Pearson J. Magnetic resonance imaging in the diagnosis of focal granulomatous meningoencephalitis in two dogs. Veterinary Radiology & Ultrasound 1996;37:424-427.
4. Dzyban LA, Tidwell AS. Imaging diagnosis - granulomatous meningoencephalitis in a dog. Vet Radiol Ultrasound 1996;37:428-430.
5. Kippenes H, Gavin PR, Bagley RS, et al. Magnetic resonance imaging features of tumors of the spine and spinal cord in dogs. Veterinary Radiology & Ultrasound 1999;40:627-633.
Acknowledgements:
Thanks to Billy Thomas, Bill Adams, Don Thrall and Ian Robertson