Intratracheal Leiomyosarcoma in a 13-Year-Old German Riding Pony Mare.

Intratracheal leiomyosarcoma, a rare type of tumor originating in the trachea, was diagnosed and partially removed in a 13-year-old German Riding Pony mare with severe respiratory distress, resulting in significant clinical improvement. The study demonstrates the successful use of transendoscopic electrosurgical excision as a treatment option for this uncommon condition in horses.

Case Presentation and Clinical Signs

• A 13-year-old German Riding Pony mare exhibited progressive respiratory noise and mixed dyspnoea which rapidly worsened into respiratory distress.
• Clinical examination revealed:
  • Marked rattling sounds heard during both inspiration and expiration from the trachea.
  • Severe, rattling vesicular lung sounds indicating airway compromise.
• Arterial blood gas analysis showed moderate hypoxaemia, with partial pressure of arterial oxygen measured at 76 mmHg at rest.

Diagnostic Procedures

• Upper airway endoscopy identified a distinct pink, cauliflower-like pedunculated mass.
• The mass originated from the dorsal tracheal wall approximately 15 cm cranial to the tracheal bifurcation.
• The lesion caused an estimated 60% obstruction of the tracheal lumen, explaining the respiratory symptoms.

Treatment Approach

• The mass was removed via transendoscopic electrosurgical excision, a minimally invasive technique using an endoscope and electrosurgical tools.
• Complete removal with tumour-free margins was not achieved, indicating possible residual tumor tissue.
• Peri-operative management involved:
  • Antimicrobial therapy to prevent infection after surgery.
  • Anti-inflammatory medication to control inflammation.
  • Bronchodilatory therapy to ease airway constriction and improve breathing.

Histopathological Findings

• Microscopic examination of the excised tissue confirmed the diagnosis of leiomyosarcoma, a malignant tumor derived from smooth muscle cells.

Postoperative Outcomes and Follow-Up

• Rapid clinical improvement was observed after surgery, with amelioration of respiratory distress symptoms.
• One month post-surgery, follow-up endoscopy showed proper healing of the surgical site.
• A small vascularized tissue mass within the scar was noted; this was suspicious for residual tumor.
• At a seven-month follow-up, no significant tumor progression was detected, suggesting stability of the residual lesion.

Significance and Implications

• This case highlights that tracheal leiomyosarcoma, although rare, should be considered in differential diagnoses for horses presenting with respiratory distress and airway obstruction.
• Transendoscopic electrosurgical excision is demonstrated as a feasible and minimally invasive therapeutic option for removing intratracheal masses in horses.
• Careful monitoring of residual tumor growth is essential, as complete excision may not always be possible.