Equine Progressive Ethmoid Hematoma Study Guide

Overview and Clinical Importance

Progressive Ethmoid Hematoma (PEH) is a nonneoplastic, locally destructive, well-encapsulated mass of the nasal passages and paranasal sinuses in horses. Despite its tumor-like appearance and progressive growth, PEH is technically benign. The condition accounts for approximately 4-8% of all sinonasal disease in horses and represents an important differential diagnosis for any horse presenting with epistaxis.

PEH develops from an aberrant vasoproliferative response within the submucosa of the ethmoid turbinates or paranasal sinuses. The mass expands through repeated hemorrhage into the submucosa, causing the mucosa to stretch and thicken, forming the characteristic capsule. Without treatment, the hematoma progressively enlarges, potentially causing significant airway obstruction and facial deformity.

Relevant Anatomy

Understanding equine paranasal sinus anatomy is essential for comprehending PEH development and treatment planning. The equine paranasal sinus system consists of seven pairs of sinuses: the frontal sinus, dorsal conchal sinus, ventral conchal sinus, rostral maxillary sinus, caudal maxillary sinus, sphenopalatine sinus (divided into sphenoidal and palatine portions), and middle conchal sinus.