46-Day-Old Female Thoroughbred

Signalment & History

  • This patient presents to your clinic with dyspnea and fever.
  • You order thorax radiographs.

    Findings

  • There is an unstructured interstitial to alveolar pattern within the ventral aspect of left caudal lung lobe, and an unstructured interstitial pattern within the ventral aspect of the right caudal lung lobe (green oval).
  • Multifocal round soft tissue opaque nodules are present in the right and left caudal lung lobes (white arrowhead).
  • A moderate amount of gas is seen outlining the tracheal walls in the caudal cervical and cranial mediastinal region.¬†(blue arrows).

Multiple open physes are seen and are consistent with the age of the patient


Diagnosis

  • This patient is diagnosed with Rhodococcus pneumonia or bacterial pneumonia with pulmonary abscesses.
  • Mild pneumomediastinum, may be iatrogenic; however, tracheal or esophageal injury cannot be excluded.

 Pneumonia in foal

  • Rhodococcus Equi has worldwide distribution and is know to produce purulent pneumonia. It is the most important cause of disease in foal between 1 and 6 months.
  • The infection is by Inhalation and ingestion routes, with a higher incidence in foal with failure in the transfer of maternal immunity.
  • Three clinical forms of the disease have been recognized:
  1. Acute pneumonia
  2. Chronic suppurative pneumonic form with extensive pyogranulomatous abscesses
  3. Intestinal form associated with mesenteric lymphadenitis (less common)

Radiographic signs of pneumonia in foals

  • Thoracic radiography is used to assess the severity of pneumonia and the response therapy.
  • The more common finding is an alveolar pattern characterized by ill-defined regional consolidation. The consolidated lesions are more often seen as nodular and Cavitary lesions compatible with pulmonary abscess. Pulmonary lymphadenopathy may also be present.
  • Non-septic immune mediates polysynovitis can be a consequence in approximately one-third of cases, particularly in the tibiotarsal and stifle joint. And septic arthritis and osteomyelitis due to bacteremic spread may affect different joint.

Ultrasonographic signs of pneumonia in foals

  • Ultrasonography is a helpful diagnostic tool when lung involvement includes peripheral areas. However, in most horses and foals with pulmonary abscessation, the periphery of the lung is affected enabling the ultrasonographer to successfully image some of the abscesses.
  • Ultrasonographically, abscess may or may not be surrounded by an echogenic fibrous capsule. The center may appear hypoechoic, isoechoic or septate, depending upon the type of fluid present. Acoustic enhancement from the far wall may occur if fluid filled. Additionally, if multiple small hyperechoic foci (suggestive of gas), are present within the abscess, a gas producing bacteria or communication with a bronchus should be considered.
  • Ultrasonographic visualization of consolidated lung occurs because of the replacement of alveolar air with fluid or cells producing an acoustic window.

Pulmonary consolidation is typically characterized as a poorly defined, hypoechoic (when compared to muscle) region that extends into the lung parenchyma and may contain one or a combination of the following structures within its center: air or fluid bronchograms, pulmonary vessels, or areas of trapped air. It is usually present in the ventral lung margins. It can be differentiated from abscess because bronchi and vessels are absent from the center of an abscess.Sonogram of the thorax from a 3-month-old thoroughbred with pulmonary abscessation secondary to Rhodococcus Equi pneumonia. Note the well-defined, circular hypoechoic region in the periphery of the lung, consistent with a pulmonary abscess. There is no evidence of pulmonary vessels or bronchi. The reverberation artifact deep to the abscess is a result of gas shadowing created by the interface of aerated lung deep to the abscess (Ramirez et al., 2004).
Sonogram of the thorax from a 4-month-old Thoroughbred with pulmonary consolidation secondary to Rhodococcus Equi pneumonia. Note the ill-defined hypoechoic region with a hyperechoic margin in the periphery of the lung. Pulmonary bronchi (arrow) within the lung parenchyma give it a liver-like appearance. The hyperechoic margin is indicative of air within the adjacent aerated lung.(Ramirez et al., 2004)

References

  • Takai, S. epidemiology of Rhodococcus Equi infections: a review. Veterinary microbiology 56 (1197) 167-176.
  • Giguere, S. and Prescott, J. clinical manifestations, diagnosis, treatment, and prevention of Rhodococcus Equi infections in foals. Veterinary Microbiology. 56 (1997) 312-334.
  • Ramirez et al. Diagnostic contribution of thoracic ultrasonography in 17 foals with Rhodococcus equi pneumonia. Veterinary Radiology and Ultrasound, vol 45, No. 2, 2004, pp 172-176.
  • Lamb et al, thoracic radiography in the neonatal foal: a preliminary report. Veterinary Radiology and Ultrasound, Vol. 31, No. 1, 1990; pp 11-16.