NAVLE Respiratory

Equine Progressive Ethmoid Hematoma Study Guide

📅 March 28, 2026 ⏱ 25 min read 👁 1 views

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.

Parameter	Details
Age	Most common in middle-aged horses (mean 9.9 years). Range: less than 1 year to 20+ years. Most commonly seen in horses greater than 6 years old.
Breed	Thoroughbreds and Arabians are overrepresented. Also reported in Warmbloods and other breeds.
Sex	No significant sex predilection, though some early reports suggested higher incidence in males.
Laterality	Unilateral in 50-84% of cases. Bilateral involvement in 16-50% of cases.
Prevalence	Accounts for 4-8% of horses with sinonasal disease at referral hospitals.

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.

The ethmoid labyrinth is located at the caudal aspect of the nasal cavity and represents the most common site of origin for PEH. The ethmoid turbinates are thin, scroll-like bones covered by highly vascular respiratory mucosa. The rich vascular supply of this region predisposes it to hemorrhagic lesion development.

High-YieldAll equine paranasal sinuses communicate with the middle nasal meatus via the nasomaxillary aperture. This explains why lesions originating in the ethmoid region can extend into multiple sinus compartments and the nasal passage.

Clinical Sign	Clinical Significance
Epistaxis	Low-volume, intermittent, unilateral (or bilateral with bilateral lesions). Often blood-tinged serous discharge.
Respiratory noise	Stertorous breathing when mass obstructs nasal airflow. More common with large or nasally-extending lesions.
Reduced airflow	Decreased airflow from affected nasal passage. May cause exercise intolerance in performance horses.
Facial deformity	Rare. Occurs only with very large, long-standing lesions causing bone remodeling.
Malodorous breath	May occur with secondary infection or tissue necrosis within the sinus.
Other signs	Head shyness, headshaking, exophthalmos (rare), coughing (rare).

Etiology and Pathophysiology

Etiology

The exact cause of PEH remains unknown. Proposed etiologies include chronic infection, repeated submucosal hemorrhage, trauma, congenital abnormalities, and aberrant angiogenesis. However, none of these theories have been definitively proven. Some researchers have suggested a possible association between PEH and paranasal sinus cysts based on histologic evidence of repeated hemorrhages within cyst walls, but this relationship remains unconfirmed.

Pathophysiology

PEH develops as an angiomatous mass originating from the mucosal lining of the ethmoid conchae or, less commonly, from the walls of the maxillary or frontal sinuses. The lesion expands through a cycle of repeated submucosal hemorrhage, which causes the overlying mucosa to stretch and thicken, forming the characteristic encapsulating membrane.

As the hematoma enlarges, it follows the path of least resistance, extending into adjacent structures. Large hematomas typically start within the ethmoid labyrinth, while smaller lesions may originate on the sinus floor. The mass commonly extends ventrally into the nasal passage, where it becomes visible on endoscopy, or dorsally into the frontal or maxillary sinuses.

Pressure necrosis of surrounding bone occurs as the hematoma expands, though facial distortion is relatively uncommon except in advanced cases. Ulceration of the overlying mucosa leads to the characteristic intermittent epistaxis.

Condition	Key Differentiating Features	Prognosis
Paranasal sinus cyst	Fluid-filled cavity with epithelial lining. Facial swelling more common. May have bony spicules in wall.	Good with surgical drainage/excision
Nasal polyp	Pedunculated, gelatinous mass. Less hemorrhagic. Often arise from ethmoidal conchae.	Good with surgical removal
Sinonasal neoplasia	Invasive, destructive. SCC most common. Older horses. Purulent discharge, bone destruction.	Poor - often extensive at diagnosis
Guttural pouch mycosis	Fungal plaques visible on endoscopy. Profuse epistaxis (often fatal). Dysphagia, cranial nerve deficits.	Guarded - risk of carotid rupture
EIPH	Exercise-associated. Bilateral epistaxis. BAL positive for hemosiderophages.	Variable - depends on severity
Sinonasal mycosis	Fungal granuloma or plaque. Often secondary to PEH surgery. Fibrinonecrotic appearance.	Guarded with antifungal treatment

Signalment and Epidemiology

Treatment	Indications and Technique	Considerations
Intralesional Formalin Injection	Small lesions (less than 5cm) accessible via endoscope. Use 4% formaldehyde (10% formalin) injected transendoscopically. Repeat every 3-4 weeks until resolution.	Minimally invasive, standing procedure. Mean 5-7 injections needed. Risk of sinusitis, conchal necrosis, cribriform plate penetration.
Nd:YAG Laser Ablation	Lesions less than 5cm in nasal fundus. Noncontact technique at 60W power. Multiple sessions often required.	Standing procedure. Reduced hemorrhage. Not suitable for sinus-extending lesions. 70% success rate reported.
Surgical Excision (Frontonasal Bone Flap)	Large lesions, sinus involvement. Bone flap provides access for complete excision and visualization of origin for radical debridement.	Most complete removal. Significant hemorrhage risk (prepare blood transfusion). 20-50% recurrence rate. Can be combined with laser.
Cryosurgery	Adjunct to surgical excision. Application of liquid nitrogen to lesion base after debulking.	May reduce recurrence. Risk of damage to cribriform plate and adjacent structures. Freezing depth difficult to control.

Clinical Signs

Cardinal Clinical Sign

Mild, intermittent, spontaneous, unilateral epistaxis is the hallmark clinical sign of PEH. The epistaxis is characteristically low-volume and spontaneous (not associated with exercise), distinguishing it from exercise-induced pulmonary hemorrhage (EIPH).

Additional Clinical Signs

NAVLE TipThe key clinical feature distinguishing PEH from EIPH is that PEH-associated epistaxis is typically spontaneous, unilateral, and NOT associated with exercise. EIPH produces bilateral epistaxis during or immediately after strenuous exercise.

Factor	Impact on Prognosis
Unilateral vs. Bilateral	Bilateral lesions have higher recurrence rate (50%) compared to unilateral (7-20%)
Lesion Size	Smaller lesions (less than 5cm) have 99% recovery; larger lesions 80-90% recovery
Overall Recurrence	17-50% recurrence within months to years, regardless of treatment modality
Without Treatment	Progressive enlargement leading to airway obstruction and dyspnea - treatment recommended

Diagnosis

Diagnosis of PEH relies on a combination of clinical history, physical examination findings, and diagnostic imaging. Definitive diagnosis requires histopathologic examination of the removed tissue.

Endoscopy

Upper airway endoscopy is the primary diagnostic tool for visualizing PEH extending into the nasal passage. The characteristic endoscopic appearance includes:

Smooth, glistening, multicolored mass (yellow, yellow-green, yellow-gray, red, or purple)
Spherical or lobulated shape with well-defined capsule
Petechial hemorrhages or surface erosions on the capsule
Origin from the ethmoid region (caudal nasal cavity)
May extend rostrally toward nares or caudally into nasopharynx

Radiography

Skull radiographs (minimum four views: lateral, dorsoventral, and bilateral oblique projections) can demonstrate:

Well-circumscribed, smooth-bordered soft tissue opacity
Single or multilobular rounded opacities in the ethmoid region
Loss of normal laminated appearance of ethmoid turbinates
Extension into frontal, maxillary, or sphenopalatine sinuses

Limitation: Radiography may fail to detect small lesions or accurately predict lesion location in approximately 30% of cases. Bilateral involvement is detected radiographically in only 25% of cases where it actually occurs.

Computed Tomography (CT)

CT is the gold standard imaging modality for evaluating PEH. Benefits of CT include:

Superior visualization of lesion extent and sinus involvement
Detection of bilateral disease (missed in 60% of cases by radiography alone)
Better assessment of sphenopalatine sinus involvement
Differentiation between fluid and solid mass lesions
Surgical planning for complete excision

CT characteristics of PEH: Well-defined, round to ovoid, soft tissue attenuating mass. May show mixed or hyperattenuating swirling pattern. Peripheral enhancement possible on contrast studies. Located in ethmoid region with extension into adjacent sinuses.

High-YieldIn one study, CT provided new diagnostic information affecting treatment in 63% of horses. Bilateral disease was undetected prior to CT in 5 of 8 horses with bilateral involvement. Always recommend CT for surgical planning when available.

Histopathology

Histopathologic examination is required for definitive diagnosis. Characteristic findings include:

Nonneoplastic angiomatous mass covered by respiratory epithelium
Fibrous capsule lined by respiratory epithelium
Stroma containing blood, fibrous tissue, and hemosiderin-laden macrophages
Evidence of recent and older hemorrhage
Occasional calcareous deposits and necrotic debris
Giant cells and inflammatory infiltrate

Differential Diagnosis

The differential diagnosis for horses presenting with epistaxis and sinonasal masses includes:

Treatment Options

Treatment selection depends on lesion size, location, extent of sinus involvement, equipment availability, and economic considerations. All treatment modalities carry significant risk of recurrence.

High-YieldIntralesional formalin injection using 4% formaldehyde solution is a commonly tested treatment modality. The solution is injected transendoscopically until the lesion distends and leakage occurs. Treatments are repeated at 3-4 week intervals. Complete resolution occurs in approximately 60% of cases after a median of 5 injections.

Prognosis

The prognosis for PEH is guarded to fair due to the high recurrence rate regardless of treatment modality. Key prognostic factors include:

NAVLE TipRegular endoscopic re-evaluation every 6 months post-treatment is recommended to detect recurrence early. Both nasal passages should always be examined since bilateral involvement occurs in up to 50% of cases and may develop on the contralateral side after successful unilateral treatment.

Memory Aids

PEH Key Features: "ETHMOID"

Epistaxis - intermittent, spontaneous, unilateral
Thoroughbreds predisposed
Hemosiderin-laden macrophages on histopath
Middle-aged horses (mean ~10 years)
Origin from ethmoid turbinates
Injection of formalin for treatment
Diagnosis by endoscopy (multicolored mass)

PEH vs EIPH: "When does it bleed?"

PEH = Spontaneous (at rest), unilateral, low volume

EIPH = Exercise-induced, bilateral, higher volume

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