Recently, the department had two patients, both with very severe head trauma, who underwent craniotomy. The patients were progressively awake after the surgery, but both experienced significant swelling in one eye and were unable to open their eyes. The eye itself was ruled out, and both were diagnosed with traumatic carotid cavernous sinus fistula through cerebral angiography, and were fully recovered through interventional therapy. How does carotid cavernous sinus fistula form? Most carotid cavernous sinus fistulas are caused by trauma. The cavernous sinus is a cavity-like structure, 2-3 cm in size, located on either side of a bony structure called the pterygoid saddle in the center of the skull base. The cavernous sinus is a venous cavity that contains venous blood. The internal carotid artery is the most important arterial blood vessel in the body supplying blood flow to the brain and there is one on one side. As the internal carotid artery travels from the neck towards the cranial cavity, a portion of it will be located entirely within the cavernous sinus, and this section is called the cavernous sinus segment of the internal carotid artery. When head trauma occurs, a fracture of the base of the skull may occur, and some tiny pieces of the fracture may puncture the internal carotid artery when the trauma occurs, causing it to rupture, and the arterial blood flows into the cavernous sinus, which is filled with venous blood. This is actually a very lucky situation. If the internal carotid artery is punctured at any other location, the patient will often die due to hemorrhage, and there is almost no chance of survival. The vein that drains venous blood from the eye is primarily the superior ophthalmic vein, which drains venous blood from the eye to the cavernous sinus. However, in the case of a carotid cavernous sinus fistula, the flow of arterial blood into the cavernous sinus due to very high pressure backs up this mixed arterial and venous blood into the eye through reflux in the superior ophthalmic vein, creating the typical ocular symptoms. The ocular symptoms of carotid cavernous sinus fistula are mainly protruding eyeballs with significant congestion, and patients often feel their eyes are distended and unable to open them. Most patients can feel a ringing sound inside the skull, which is always persistent and consistent with the rhythm of the patient’s pulse and heartbeat. With this presentation, it is important to consider the possibility of a carotid cavernous sinus fistula. If the doctor uses a stethoscope in front of the patient’s temples or above the eyes, etc., listening to the patient’s pulse rhythm consistent with the murmur, basically may be sure that the carotid cavernous sinus fistula. In some patients, the small size of the fistula does not result in an intracranial murmur, which can make the diagnosis more difficult. The diagnosis of carotid cavernous sinus fistula is confirmed by digital subtraction cerebral angiography (DSA). Other tests, such as CT of the eye to detect thickened suprachoroidal veins, and CT of the neck and cerebral angiography (CTA) are also capable of detecting the fistula. The treatment of carotid cavernous sinus fistula is mainly through interventional therapy, the most commonly used is to put a special detachable balloon into the cavernous sinus, inflate and then occlude the fistula to induce thrombosis in the cavernous sinus, to achieve the purpose of long-term healing.