Cystic Sinus

• Occurs in horses
• Usually originate in maxillary sinus
• Can extend to other sinuses
• Some have dentigerous origin
• Many are congenital
• Histology:
  • Lined with pseudostratified epithelium overlying granulation tissue
  • Haemorrhage under the epithelium
  • Cyst walls contain bone spicules with osteoclastic and osteoblastic activity