The sigmoid sinus is a large vein within the skull that drains blood from the brain. It forms an S-shaped curve as it travels through the temporal bone, behind the ear, eventually connecting to the internal jugular vein. A sigmoid sinus diverticulum is an abnormal outpouching or sac-like protrusion from the wall of this blood vessel. While often discovered incidentally and remaining without symptoms, its presence can sometimes lead to notable symptoms and potential complications.
What is Sigmoid Sinus Diverticulum?
A sigmoid sinus diverticulum is a balloon-like bulge extending from the sigmoid sinus wall, often pushing into the adjacent mastoid bone behind the ear. This anatomical variation can occur with or without a complete absence of the bone covering the sinus, known as dehiscence. The sigmoid sinus is a paired dural venous sinus, collecting deoxygenated blood from various parts of the brain and skull.
The precise cause of a sigmoid sinus diverticulum is not always clear. It is believed to result from a localized weakness in the sinus wall or chronic low-pressure erosion of the surrounding bone. Some instances might be present from birth, while others may develop over time. Although many individuals with a sigmoid sinus diverticulum experience no symptoms, these outpouchings are found in about 1% of the general population. However, their prevalence significantly increases to approximately 23-24% among individuals who experience pulsatile tinnitus.
Why Sigmoid Sinus Diverticulum Can Be Serious
A sigmoid sinus diverticulum can become a concern due to the symptoms and complications it may cause. The most common symptom is pulsatile tinnitus, a rhythmic, pulsing sound in the ear synchronized with the heartbeat. This sound can be described as a whooshing or throbbing noise. The diverticulum causes turbulent blood flow within the sinus. This turbulence, combined with a potentially thinned or absent bony barrier, allows the sound of blood flow to be transmitted directly to the nearby inner and middle ear structures.
Beyond pulsatile tinnitus, a sigmoid sinus diverticulum can also contribute to other issues. In some cases, it may be associated with hearing loss, although the specific type of hearing loss can vary. The presence of a diverticulum can also be linked to symptoms related to elevated intracranial pressure, such as headaches. This connection is sometimes observed in patients with idiopathic intracranial hypertension (IIH), a condition characterized by increased pressure within the skull without an obvious cause. The diverticulum might alter normal venous drainage, potentially contributing to these pressure changes.
How Sigmoid Sinus Diverticulum is Diagnosed and Treated
Diagnosing a sigmoid sinus diverticulum typically involves clinical evaluation and specialized imaging studies. When a patient reports symptoms like pulsatile tinnitus, medical professionals often suspect a vascular cause. Initial diagnostic steps usually include imaging techniques such as Magnetic Resonance Imaging (MRI) with venography (MRV) or Computed Tomography (CT) with venography (CTV). High-resolution CT scans of the temporal bone are particularly useful for visualizing the bony anatomy and identifying the diverticulum or any associated bone defects. In some instances, a cerebral angiogram may be performed to provide a detailed view of the blood flow dynamics within the sinus.
Treatment approaches for sigmoid sinus diverticulum depend on the severity of symptoms and the specific anatomical features of the diverticulum. For individuals with mild or no symptoms, a conservative approach involving observation and monitoring may be sufficient. However, for those experiencing significant pulsatile tinnitus or other debilitating symptoms, interventional treatments are often considered. These can include:
Endovascular procedures, where a stent might be placed within the sigmoid sinus to improve blood flow and reduce turbulence, or the diverticulum itself might be coiled to block the turbulent flow.
Surgical repair, such as diverticulectomy (removal of the outpouching), venoplasty (reshaping the sinus), or resurfacing the dehiscent bone over the sinus to restore the sound barrier.
Living with Sigmoid Sinus Diverticulum: Outlook and Management
For many individuals, a sigmoid sinus diverticulum is an incidental finding that does not cause any symptoms, and thus requires no specific treatment beyond continued monitoring. In these asymptomatic cases, regular follow-up appointments may be recommended to ensure that no new symptoms develop. For those who do experience symptoms, particularly pulsatile tinnitus, the outlook is generally positive with appropriate management.
Treatments for symptomatic sigmoid sinus diverticulum are often effective in alleviating or resolving the pulsatile tinnitus. Patients who undergo interventional procedures or surgical repair frequently report significant relief from their symptoms. It is important for individuals to maintain realistic expectations regarding symptom resolution, as complete disappearance of all symptoms may not always occur. Long-term management typically involves ongoing communication with medical professionals to address any persistent or new concerns and to ensure the continued effectiveness of any treatment received.