Progressive ethmoidal hematomas (PEHs) in horses are non-cancerous masses that develop from the ethmoidal labyrinth. This a structure with a high concentration of blood vessels within the horse’s nasal sinuses. [1]

PEHs are composed of blood surrounded by a thin layer of connective tissue, making them susceptible to damage and profuse bleeding. [1] The most common presentation of ethmoidal hematomas is bleeding from one or both nostrils.

Veterinarians diagnose ethmoidal hematomas in horses using an endoscope passed into the nasal cavity. Treatment options include surgical removal, laser reduction, cryosurgery, and formalin injection.

The overall prognosis of ethmoidal hematomas is poor, as recurrence is very common despite treatment. Many horses with ethmoidal hematomas can be managed with repeated treatments when symptoms redevelop.

Progressive Ethmoidal Hematomas in Horses

Progressive ethmoidal hematomas are benign masses that can form at the back of the horse’s nasal passages. When PEHs develop in horses, they can grow and spread into the nasal cavity and the surrounding sinuses. [1]

PEHs in horses are usually not life-threatening, but they can limit a horse’s performance and may lead to sinus and airway issues if not addressed. [1][3] This condition is relatively uncommon in horses but may be suspected if a horse experiences recurrent nosebleeds unrelated to exercise. [1]

The name “progressive ethmoidal hematomas” denotes the following:

  • Progressive: Indicates that the condition tends to worsen over time if not treated
  • Ethmoidal: Originates from the ethmoidal turbinates, which are small, scroll-like bony structures covered with mucous membranes, located at the back of the nasal cavity​
  • Hematomas: Blood-filled masses that results from blood pooling or clotting within the tissue​


The underlying cause of PEHs in horses is unknown, however damage to the protective layer of mucus-secreting tissue lining the nasal sinuses is likely a trigger. [1]

Damage to the mucosa lining causes small bleeds underneath the surface, resulting in a pocket of blood. [2] It is theorized that continued irritation and damage enlarges the pocket, eventually forming an ethmoidal hematoma. [2]

Around half of horses that have PEH have a mass in both nasal sinuses (bilateral). [1]

Currently, the only predisposing risk factor for PEH is increasing age, as rates of occurrence are higher in older horses. [1]


The main symptom of PEH is periodic bloody discharge from a nostril (epistaxis). [1] Horses with bilateral PEHs may have bleeding from both nostrils. [1]

Other symptoms of PEH may include: [1][3]

  • Swelling of the face
  • Noisy breathing
  • Bad breath
  • Difficulty breathing
  • Coughing
  • Head shaking


Periodic bloody discharge from the nose usually suggests a diagnosis of ethmoidal hematoma.

Confirming the diagnosis involves endoscopy, a procedure in which a camera is used to examine the inside of the nasal passages and visualize the mass. [1] On endoscopy, ethmoidal hematomas are a purple-red or green-yellow mass that obstructs the nasal cavity. [2]

Often, PEH masses obstruct the entire nasal cavity, which makes it challenging to confirm the exact size and location of the mass on endoscopy. [2] Other diagnostic tests that may help determine the extent and size of the mass include: [1][2]

  • X-rays of the head
  • Computed tomography (CT scan)
  • Magnetic resonance imaging (MRI)

Differential Diagnosis

Other types of masses can also occur within the nasal sinuses. To confirm that the mass is an ethmoidal hematoma, a biopsy (small sample of tissue) is required to analyze what type of cells are present in the mass. [1]

Other masses that can resemble PEHs include: [2]

  • Nasal polyps
  • Fungal infections
  • Traumatic injuries from a foreign body entering the nasal passage
  • Tumors