11-year-old spayed female Miniature Schnauzer

1. The vertebral body of the first thoracic vertebra (Th1) is diffusely hyperintense on T1, T2 and STIR images and displays moderate diffuse contrast enhancement. There is moderate ventral and mild dorsal attenuation of the subarachnoid fluid signal at the level of Th1 on HASTE images. There is loss of the normal hypointense cortical bone signal at the left cranioventral aspect of the Th1 vertebral body with mild contrast enhancement of the soft tissues adjacent to the cortical disruption. Mild contrast enhancement of the soft tissues along the right dorsal aspect of Th1 is also noted. The ventral vertebral sinus is moderately distended from the caudal aspect of C7 to the cranial aspect of Th2.
2. In addition to the changes associated with the first thoracic vertebra there are T1 and T2 hyperintense areas associated with multiple vertebral bodies of the cervical and cranial thoracic spine, most obvious at C7 and Th2. These hyperintense areas attenuate on STIR and do not show evidence of pathologic contrast enhancement.
3. There is mild decrease in normal T2 signal intensity of all intervertebral discs except C2/3 and C3/4. There is very mild herniation of the intervertebral disc C4/5 without evidence of spinal cord compression. There is a large, fusiform, T2 and T1 hyperintense mass within the right axilla which does not display contrast enhancement and is hypointense on fat suppressed post contrast images.

Summary

1. Monostotic lesion of the first thoracic vertebra. The changes are centered on the medullary cavity of the vertebral body, with suspicion of mild focal cortical lysis of the ventral vertebral body. Round cell neoplasia (e.g. plasma cell tumor, lymphoma or histiocytic sarcoma) was considered the most likely differential diagnosis, although a primary bone tumor or a single metastatic lesion could not be excluded. Tissue sampling was recommended for further evaluation.
2. Intensity changes of other vertebral bodies are consistent with incidental fatty degeneration of bone marrow.
3. Mild multifocal disc degenerative changes are also incidental.
4. Incidental right axillary lipoma

Diagnosis

CT-guided fine needle aspiration of the vertebral body of T1 was performed (see CT image) and yielded a diagnosis of plasma cell tumor.

Plasma cell neoplasia is a variant of lymphoproliferative disease and may affect a variety of organs (1,2). Plasma cell tumors originating from bone marrow may be isolated but more commonly affect multiple sites (multiple myeloma). The diagnosis of multiple myeloma usually follows the demonstration of bone marrow plasmacytosis, the identification of multifocal osteolytic bone lesions, and the demonstration of serum or urine myeloma proteins. In this dog, no additional lesions were detected on MRI of the cervical spine or on pre-anesthetic thoracic radiographs. However, additional bone lesions in other areas may have gone unnoticed. Unfortunately, the dog’s owners declined further work-up, so a definitive diagnosis of isolated plasma cell tumor (vs. multiple myeloma) was not possible.

Reports on MRI findings in canine vertebral plasmacytoma and multiple myeloma are scarce. T1 hyperintensity of the lesion observed in the current patient was surprising but has been reported previously (3). Use of a fat suppressed sequence was especially helpful in this dog as additional T1 and T2 hyperintense areas in multiple vertebral bodies related to fatty degeneration of bone marrow may have resulted in an erroneous diagnosis of polyostotic bone disease.

References

1. Vail DM. Plasma cell neoplasms. In: Small Animal Clinical Oncology, 4th ed. Withrow SJ, Vail DM, eds. St. Louis: Saunders Elsevier 2007; 769-84.
2. DeNicola DB. Round cells. In: Cowell and Tyler’s Diagnostic Cytology and Hematology of the Dog and Cat, 4th ed. Valenciano AC, Cowell RL, eds. St. Louis: Elsevier Mosby 2014; 70-9.
3. Kippenes H, Gavin PR, Bagley RS, Silver GM, Tucker RL, Sande RD. Magnetic resonance imaging features of tumors of the spine and spinal cord in dogs. Vet Radiol Ultrasound 1999;40:627-33.