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  • The patient was presented to the rDVM for progressive pelvic limb weakness.
  • The owners first noticed an acute lameness after chasing a rabbit which progressed to the patient “not using her back legs” (per owners) over several days.
  • She had a history of bilateral TPLO and multifocal osteoarthritis which was being treated with gabapentin, Galliprant, and laser therapy.
  • Physical exam revealed obesity and pyrexia (104.4o F) but no other relevant abnormalities.
  • CBC was unremarkable except for a low-normal HCT of 38%. Serum biochemistry revealed the following: o ALP 638 U/L (5-160) o ALT 133 U/L (18-121) o AST 77 U/L (16-55) o TP 7.9 g/dL (5.5-7.5) o Glob 4.7 g/dL (2.4-4.0) o T4 0.9 mcg/dL (1.0-4.0)
  • A single lateral thoracic radiograph, and right and left lateral abdominal radiographs were deemed unremarkable by the rDVM.
  • Abdominal ultrasound, adrenocortical testing, and neurology referral were discussed but not pursued.
  • 5 days later the patient was presented to the ER for progressive paraparesis. No additional testing or treatments were pursued and the patient was scheduled with the neurology service later that week.
  • Neurologic evaluation revealed ambulatory paraparesis with delayed conscious proprioception in the pelvic limbs, but no other neurologic deficits. Neuroanatomic localization was T3-L3 myelopathy. MRI was pursued.
  • Within the spinal canal there are numerous (at least 10) extramedullary, variably sized, nodular, discrete structures causing variable compression of the spinal cord. The worst compression is moderate (~40% reduction in spinal cord diameter) at the level of L4-L5, compressive material being on the right side. These nodular structures demonstrate homogeneous T2w mild hyperintensity and T1w isointensity.
  • Extending along the ventral periosteal surface of T6 is a lobulated mass with similar signal characteristics to that of the nodules in the spinal canal. The cortex adjacent to this structure is thinned and intermittently difficult to visualize.
  • There are discrete peripherally T2w/STIR hyperintense regions within the medullary cavities of multiple vertebrae, some of which appear contiguous with the nodular structures in the spinal canal. These correlate with marked patchy hyperintensity in all vertebrae, particularly the sacrum and bilateral ilial wings.
  • All visible abdominal and thoracic lymph nodes (particularly the periportal, medial iliac, and tracheobronchial nodes) are severely enlarged.
  • There is an at least 4 cm diameter mass in the right caudal lung lobe surrounded by areas of consolidated lung (atelectasis vs. neoplastic infiltration).
  • The liver contains numerous discrete round to lobulated T2w hyperintense, faintly T1w hypointense masses ranging in size from 1-8 cm in diameter distributed throughout all lobes. The two largest masses are within the left medial and lateral lobes, one of which has a discrete T2w hyperintense core and gradated appearance to its thick walls. Numerous T2w/T1w hypointense, STIR hyperintense nodules are scattered throughout the subcutaneous fat.

The combined findings of extradural spinal canal nodules, intraosseous lesions, lung mass, liver mass (likely necrotic), splenic masses, and diffuse massive lymphadenopathy are most concerning for disseminated histiocytic sarcoma. Other round cell neoplasia (such as lymphoma and multiple myeloma) could be considered but are less likely.

Ultrasound guided fine needle aspiration was subsequently performed on liver mass. Cytology confirmed a diagnosis of Histiocytic Sarcoma.

  • Histiocytic sarcoma is most often diagnosed in Bernese Mountain Dogs, Rottweilers, and Flat Coated Retrievers, with a predilection for large breed dogs in general. • Histiocytic sarcoma is a differential for lung masses, particularly if they are large or occupy the entire lobe, are peripherally located, or are located in the right middle or left cranial lobes (1).
  • Multiple myeloma could have been considered regarding the osseous lesions, but is less likely to explain the size of masses in the liver. Likewise, lymphoma could be considered for the diffuse lymphadenomegaly, but would not correlate with the expansile nature of the vertebral lesions; in the available literature, spinal lymphoma typically causes medullary lysis and infiltration without substantial cortical destruction(2–5).

1. Barrett LE, Pollard RE, Zwingenberger A, Zierenberg-Ripoll A, Skorupski KA. Radiographic characterization of primary lung tumors in 74 dogs. Vet Radiol Ultrasound. 2014;55(5):480-487. doi:10.1111/vru.12154

2. Allett B, Hecht S. Magnetic resonance imaging findings in the spine of six dogs diagnosed with lymphoma. Vet Radiol Ultrasound. 2016;57(2):154-161. doi:10.1111/vru.12340

3. Auger M, Hecht S, Springer C. Magnetic Resonance Imaging Features of Extradural Spinal Neoplasia in 60 Dogs and Seven Cats. Front Vet Sci. 2021;7:610490. doi:10.3389/fvets.2020.610490

4. Kornder J, Platt S, Eagleson J, Kent M, Holmes S. Imaging diagnosis- Vertebral polyostotic lymphoma in a geriatric dog. Vet Radiol Ultrasound. 2016;57(4):E42-E45. doi:10.1111/vru.12312 5. Palus V, Volk HA, Lamb CR, Targett MP, Cherubini GB. MRI features of CNS lymphoma in dogs and cats. Vet Radiol Ultrasound. 2012;53(1):44-49. doi:10.1111/j.1740-8261.2011.01872.x