Findings:
- Within the cranioventral mediastinum, a large, partially well-defined, smoothly marginated and rounded soft tissue opaque mass is identified (yellow arrows). This mass is cranially obscured by the humerus.
- The physes are open, consistent with the patient’s young age
Conclusions:
- Cranioventral mediastinal mass, raising concerns for neoplasia, such as lymphosarcoma or less likely thymoma, Lymphadenopathy or a mass of other tissue of origin may also be considered. An abscess is thought less likely in the absence of supportive clinical signs. This mass is likely causing compression of the regional vasculature and subsequent venous congestion.
Follow-up:
Ultrasound evaluation of the mass:
A biopsy of the cranial mediastinal mass was obtained and submitted for histopathology.
Diagnosis: Mediastinal lymphoma
Note: Mediastinal masses in young horses are typically of T cell origin; however, given the small population of B cells noted in this obtained tissue, a T cell rich B cell lymphoma cannot be completely ruled out.
Given the limited medical management options, the patient was discharged with corticosteroid therapy.
A little bit more…
- Lymphomosarcoma is the most common thoracic neoplasia in horses (representing approximately half of all thoracic neoplasms) (Garber et al., Mair et al., Marqués et al., Davis et al.).
- Horses with mediastinal lymphosarcoma usually have neoplastic infiltration of other organs, especially the abdominal lymph nodes, liver, spleen and kidneys (Garber et al., Janvier et al.).
- Most prevalent clinical signs include (Garber et al.):
- Weight loss
- Jugular distension
- Ventral edema
- Muffled heart sounds
- Tachycardia
- Most horses develop pleural effusion which may result in dyspnea (Mair et al.). In horses with pleural effusion, neoplastic cells are most often identified on cytology (Garber et al., Mair et al., Marqués et al.).
- Peripheral lymphadenopathy is rarely observed (Mair et al.).
- No age predilection (juvenile to over 30 years of age) (Garber et al., De Clercq et al.).
- The use of ultrasound for the evaluation of the cranial mediastinum in horses with lymphosarcoma was previously described by Garber et al.:
- Large (usually >4cm in size) lobular mediastinal mass with varying echogenicity. Most tend to be homogeneously hypoechoic. More complex mixed echogenicity may be associated with the presence of necrosis.
- Mediastinal effusion is usually not seen.
- Variable amounts of pleural effusion.
- Thoracocentesis prior to radiographs is recommended for improved visualization of cranial mediastinal disease (Davis et al.).
- Many cases of equine lymphoma are caught too late in the progression of the disease to be treated and treatment options are very limited. Lack of clinical signs enables the cancer to grow and proliferate to a point where treatment is not viable.
- Death usually occurs within months after the emergence of clinical signs and a diagnosis is achieved (Garber et al., De Clercq et al.)
- Chemotherapy protocols are available but there is little data about efficacy and length of time for response (Garber et al.).
References:
- Garber, Jenifer L., Virginia B. Reef, and Johanna M. Reimer. “Sonographic findings in horses with mediastinal lymphosarcoma: 13 cases (1985–1992).” Journal of the American Veterinary Medical Association 205.10 (1994): 1432-1436.
- Mair, T. S., B. R. Rush, and R. L. Tucker. “Clinical and diagnostic features of thoracic neoplasia in the horse.” Equine Veterinary Education 16.1 (2004): 30-36.
- De Clercq, Dominique, et al. “Ultrasound‐guided biopsy as a diagnostic aid in three horses with a cranial mediastinal lymphosarcoma.” Veterinary record 154.23 (2004): 722-726.
- Marqués, Fernando J., et al. “Respiratory distress due to retropharyngeal and neck swelling in a horse with mediastinal lymphosarcoma.” Compend. Contin. Educ. Vet 34 (2012): E5.
- Janvier, Valentin, et al. “Ultrasonographic findings in 13 horses with lymphoma.” Veterinary Radiology & Ultrasound 57.1 (2016): 65-74.
- Davis, E. G., and B. R. Rush. “Diagnostic challenges: equine thoracic neoplasia.” Equine Veterinary Education 25.2 (2013): 96-107.
