Nosebleeds, medically termed epistaxis, are categorized into two types based on their origin. The vast majority are anterior bleeds, originating from the front of the nose where a delicate network of small vessels, known as Kiesselbach’s plexus, is easily damaged. Posterior nosebleeds are a much less common clinical event, representing only about 6% to 10% of cases requiring medical intervention. This form of bleeding is more serious because it originates from larger blood vessels located deep in the nasal cavity, often resulting in a profuse flow that is difficult to stop without professional medical assistance.
The Source of the Bleed
A posterior nosebleed originates from vessels situated on the posterior septum or the lateral wall of the nasal cavity, far from the nostrils. This location is supplied by arteries that carry a greater volume of blood at a higher pressure than the superficial vessels found near the nasal entrance. The primary culprit in most severe posterior bleeds is the sphenopalatine artery (SPA) or one of its major branches.
The sphenopalatine artery is the terminal branch of the maxillary artery, which is part of the external carotid artery system. After entering the nasal cavity, the artery typically divides into several large branches that supply the nasal septum and the lateral wall. Damage to the wall of this deeper artery releases a significant volume of blood flow. This arterial bleeding often flows backward into the throat, making it difficult to control with simple compression and increasing the severity of the episode.
Systemic Health Conditions
The rupture of these deep-seated, high-pressure vessels is frequently linked to underlying systemic health issues that compromise the integrity of the vascular system. Chronic, uncontrolled hypertension is a commonly identified factor contributing to posterior epistaxis, making it one of the most frequent causes. Persistently elevated blood pressure places continuous stress on the walls of deeper arteries, including the sphenopalatine artery. This chronic strain changes the vessel structure, increasing fragility and susceptibility to rupture.
When a hypertensive patient experiences a sudden spike in blood pressure, weakened vessels in the posterior nasal region may fail, leading to a profuse bleed. The higher pressure also makes it more difficult for the body’s natural clotting mechanisms to seal the rupture, prolonging the episode. Atherosclerosis, where plaque builds up and hardens the arterial walls, also increases risk, particularly in older adults. Hardened arteries lose elasticity and become brittle, making them prone to tearing under normal or elevated blood flow conditions.
Conditions that impair the body’s ability to form stable blood clots also turn a minor vascular tear into a persistent, severe hemorrhage. Inherited or acquired coagulation disorders, such as hemophilia, Von Willebrand disease, or liver disease, reduce the capacity of the clotting cascade. These disorders prevent the formation of a robust fibrin plug necessary to stop the flow from a high-pressure source. Similarly, certain cancers that affect blood cell production, such as leukemia, can lead to low platelet counts, compromising the initial step of the clotting process and raising the risk of prolonged posterior bleeding.
Medication and Environmental Triggers
Beyond chronic diseases, the use of certain medications and exposure to external conditions can significantly predispose an individual to posterior nosebleeds. Medications designed to thin the blood are a major contributing factor, especially when interacting with an underlying systemic condition. Anticoagulant drugs like warfarin and direct oral anticoagulants (DOACs), along with antiplatelet agents such as aspirin and clopidogrel, interfere with the normal clotting process.
For a person taking these medications, the rupture of a nasal vessel that might otherwise be minor can rapidly escalate into a serious, uncontrolled posterior hemorrhage. Patients taking these agents for conditions like atrial fibrillation or a history of stroke have an increased rate of epistaxis, and the bleeding is often more difficult to manage. The effect of these medicines is to prevent the formation of clots, which is their therapeutic goal, but this action makes controlling any accidental bleeding a challenge.
Environmental factors also play a role by affecting the delicate nasal lining, though they more commonly cause anterior bleeds. Extremely dry air, particularly in heated indoor environments or arid climates, can dehydrate the nasal mucosa, causing it to crack and expose underlying vessels. This irritation, combined with actions like forceful nose-blowing, can sometimes trigger a posterior bleed in susceptible individuals. While minor trauma usually affects the front of the nose, severe facial trauma, such as a forceful impact or fracture, can directly damage the deeper arteries, leading to an immediate and significant posterior hemorrhage.