Epithelial inclusion cyst of the equine digital flexor tendon sheath: diagnosis by ultrasonography and magnetic resonance and successful treatment by tenoscopy
Authors: Joostens Z., Vanslambrouck L., De Cock H., Mariën T.
Journal: Vlaams Diergeneeskundig Tijdschrift
Summary
# Editorial Summary A six-year-old warmblood presenting with chronic forelimb lameness and mild digital flexor tenosynovitis was found to harbour an epithelial inclusion cyst within the distal digital flexor tendon sheath—a rarely documented location for this type of benign, keratinising lesion. Ultrasonography and magnetic resonance imaging proved complementary diagnostic tools, revealing a dense, partially lamellar mass without internal vascularity and associated pressure osteolysis of the middle phalanx, which helped differentiate the cyst from more typical fluid-filled synovial pathology. Following complete tenoscopic excision and histopathological confirmation, the horse recovered well, suggesting that even substantial masses within the tendon sheath can be successfully removed via minimally invasive surgery. Given the chronic presentation and atypical imaging appearance of these lesions in this location, epithelial inclusion cysts warrant inclusion in the differential diagnosis for horses with persistent digital flexor tenosynovitis and discrete swelling of the distomedial pastern region. For practitioners managing such cases, tenoscopic approach offers a definitive, curative treatment option with a favourable prognosis for return to function, though accurate pre-operative imaging remains essential for surgical planning and case selection.
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Practical Takeaways
- •Dense, atypical mass lesions in the digital flexor tendon sheath on imaging may represent epithelial inclusion cysts rather than typical fluid-filled cysts—maintain a broad differential diagnosis
- •Tenoscopy is an effective minimally invasive approach for complete removal of even larger masses in the tendon sheath with curative outcomes
- •Chronic unexplained distal limb lameness with mild tenosynovitis warrants thorough imaging including MRI to identify space-occupying lesions that may respond well to surgical intervention
Key Findings
- •Epithelial inclusion cyst of the digital flexor tendon sheath presented as a dense mass lesion with partial lamellar architecture on ultrasound and MRI, distinct from typical cystic lesions
- •The cyst caused chronic lameness and mild tenosynovitis with pressure osteolysis of the middle phalanx
- •Complete tenoscopic excision achieved successful resolution with good prognosis for return to function