Tinnitus is a symptom defined as the perception of noise in the absence of an acoustic stimulus. Tinnitus is most commonly heard as a ringing, buzzing or hissing sound. Approximately 4% of patients with tinnitus, however, describe the sound as a pulsing noise (1). Pulsatile tinnitus that is the same rhythm as a person’s heartbeat is known as pulse-synchronous tinnitus (PST). Some of the causes of pulse-synchronous tinnitus are listed in the table below.

TABLE. Adapted from Harvey, RS, et al.(2) (Legend: Atherosclerosis = hardening of blood vessels; Arteriovenous malformation = tangle of abnormal blood vessels connecting arteries and veins; fistula = abnormal communication between two different areas of the body; idiopathic = unknown cause; sigmoid sinus = large venous sinus draining blood from the brain into the jugular vein in the neck. The sigmoid sinus is located in the mastoid bone behind the ear; dehiscence = loss of bone over an area; Glomus tumor = benign tumor that is filled with many blood vessels; Paget’s disease = disorder of bone that weakens bone and causes increased blood flow through the affected bone; anemia = low blood count; thyrotoxicosis = disorder of the thyroid that causes a hyperactive thyroid gland. The thyroid gland helps to regulate the body’s metabolism.)

Pulsatile tinnitus that is faster than a person’s heartbeat is often due to myoclonus (muscle spasm) of the muscles in the back of the throat (palatal myoclonus), or due to myoclonus of one of the small muscles in the middle ear (tensor tympani or stapedius muscle). Pulse-synchronous tinnitus is the much more common type of pulsatile tinnitus and will be the focus of this article, with an emphasis on sigmoid sinus dehiscence/diverticulum as the cause.

Pulse-synchronous tinnitus (PST) is the ability to hear one’s own blood flow (2). PST may be due to an enhanced perception of bodily sounds, such as in the case of superior semicircular canal dehiscence. (The superior semicircular canal is one of the fluid-filled, hallow balance canals of the inner ear that is normally covered by bone. A dehiscence means that the bone is absent in an area normally covered by bone.) In some cases of superior semicircular canal dehiscence, one is able to hear one’s eyes move.
 
More commonly, pulse-synchronous tinnitus is due to an abnormality in the way blood flows near the ear. Atherosclerosis, and sigmoid sinus dehiscence or sigmoid sinus diverticulum are some of the more common causes of abnormal blood flow near the ear. Atherosclerosis is a hardening of the walls of an artery (fast-flow system) or a vein (slow-flow system). Atherosclerosis may cause a narrowing of the lumen of the blood vessel. Narrowing of a blood vessel causes a turbulence in the area of narrowing. Arterial or venous narrowing is similar to narrowing the opening of a water hose. When the opening of a water hose is narrowed, for example with a thumb, the water flows out with more force, and therefore, a turbulent sound is generated.

Sigmoid sinus dehiscence or sigmoid sinus diverticulum are some of the most commonly identified causes of pulse-synchronous tinnitus, occurring in 4 – 40% of cases of PST (3-6). The sigmoid sinus is a large vein located inside the bone behind the ear, which is known as the mastoid bone (See Figure at head of this article). The sigmoid sinus drains blood from around the brain and then into the jugular vein in the neck. The sigmoid sinus is normally covered by bone. Since the mastoid bone is made up of a honeycomb type of arrangement, there are times when there is thin or no bone over the sigmoid sinus. A dehiscence over the sigmoid sinus means there is no bone over the sinus in the area of the dehiscence. A diverticulum is an abnormal outpouching or protrusion of the sinus. A diverticulum may occur in an area of weakness in the wall of the sinus. (An everyday example of a diverticulum would be a weakness in the wall of a balloon; when the balloon is filled with water, the weak portion of the balloon dilates away from the main portion of the balloon, creating a diverticulum.) The bone covering the sigmoid sinus acts as a sound barrier for the normal pulsing sounds of venous blood passing through the sinus. If the bony barrier is removed, as in the case of sigmoid sinus dehiscence, the normal pulsing sounds of the sinus may travel to the nearby middle and inner ear. A sigmoid sinus diverticulum, on the hand, causes turbulent blood flow in the area of the diverticulum.

Diagnosis
 
Several factors are used to try to determine the cause of pulse-synchronous tinnitus. These factors include determining an individual’s past and current health history, performing a targeted physical exam and obtaining radiographic imaging studies. For example, physical examination can often identify if PST is due to a venous cause. In many cases of venous PST, the tinnitus intensity is changed when the jugular vein in the neck is compressed, or when the neck is rotated away from the side experiencing PST.  
There are several radiographic imaging studies used to determine the cause of pulse-synchronous tinnitus. These studies include magnetic resonance imaging (MRI) of the brain, magnetic resonance angiography (MRA) of the brain and/or neck to evaluate arteries in the brain/neck, magnetic resonance venography (MRV) brain and/or neck for the venous system, CT temporal bones, CT angiography of the brain, and cerebral angiogram (similar to cardiac angiogram for the heart). Each of these imaging studies provides unique information. Which study, or studies, is/are used is determined by the possible cause for PST based on the individual’s history and physical exam. Sigmoid sinus dehiscence/diverticulum is best seen on a dedicated CT radiographic imaging of the ear and surrounding structures (CT temporal bones). The images below are examples of a normal sigmoid sinus (image on left) and sigmoid sinus dehiscence (image on right). [CT: White structures = bone; Black = air; Gray = soft tissue]

Pulse-synchronous tinnitus due to sigmoid sinus dehiscence/diverticulum occurs most commonly on the right side. This right-sided frequency is believed to be due to the finding that the right side is often the larger, and therefore, dominant side of the cerebral (brain) venous system (7). Right-sided dominance of the sigmoid sinus means that an increased diameter makes turbulent flow more likely than on the other side (7).

Treatment
 
Sigmoid sinus dehiscence and sigmoid sinus diverticulum are potentially surgically correctable causes for pulse-synchronous tinnitus. Surgical treatment of sigmoid sinus abnormalities is performed under general anesthesia and patients typically go home the same day or stay one night in the hospital. The procedure involves an incision behind the ear followed by opening the mastoid bone behind the ear. The sigmoid sinus is exposed and the defect(s) identified. In the case of dehiscence, the area of bone dehiscence is repaired using three layers: bone dust obtained from opening the mastoid bone, temporalis fascia (thin tissue over a muscle exposed before the mastoid bone is opened), and synthetic bone cement, as the last layer used for closure. In most cases of a sigmoid sinus diverticulum, the diverticulum is first made considerably smaller with cautery. Then, the three layers as described for dehiscence repair are used to cover the diverticulum.

Results of Surgical Treatment

Complete resolution of pulsatile tinnitus from sigmoid sinus dehiscence/diverticulum surgical repair has been reported to occur in 74% of patients, with the remainder achieving partial resolution (14%) or no improvement (12%) (8). Our practice has seen similar results using the surgical techniques outlined above for PST and sigmoid sinus wall abnormalities.

Final Thoughts

Despite the fact that sigmoid sinus wall abnormalities are one of the more commonly identifiable causes for pulse-synchronous tinnitus, there are times when the cause of PST cannot be identified. Various authors have reported identifying a definitive cause for PST in 68 – 72% of patients with pulsatile tinnitus (6,9).

References
 
1.         Stouffer JL, Tyler RS. Characterization of tinnitus by tinnitus patients. J Speech Hear Disord 1990; 55:439-453.
2.         Harvey RS, Hertzano R, Kelman SE, Eisenman DJ. Pulse-synchronous tinnitus and sigmoid sinus wall anomalies: descriptive epidemiology and the idiopathic intracranial hypertension patient population. Otol Neurotol 2014; 35:7-15.
3.         Grewal AK, Kim HY, Comstock RH, 3rd, Berkowitz F, Kim HJ, Jay AK. Clinical presentation and imaging findings in patients with pulsatile tinnitus and sigmoid sinus diverticulum/dehiscence. Otol Neurotol 2014; 35:16-21.
4.         Schoeff S, Nicholas B, Mukherjee S, Kesser BW. Imaging prevalence of sigmoid sinus dehiscence among patients with and without pulsatile tinnitus. Otolaryngol Head Neck Surg 2014; 150:841-846.
5.         Zeng R, Wang GP, Liu ZHet al. Sigmoid Sinus Wall Reconstruction for Pulsatile Tinnitus Caused by Sigmoid Sinus Wall Dehiscence: A Single-Center Experience. PLoS One 2016; 11:e0164728.
6.         Mattox DE, Hudgins P. Algorithm for evaluation of pulsatile tinnitus. Acta Otolaryngol 2008; 128:427-431.
7.         Friedmann DR, Eubig J, McGill M, Babb JS, Pramanik BK, Lalwani AK. Development of the jugular bulb: a radiologic study. Otol Neurotol 2011; 32:1389-1395.
8.         Wang GP, Zeng R, Ma XB, Liu ZH, Wang ZC, Gong SS. Surgical treatment of pulsatile tinnitus caused by the sigmoid sinus diverticulum: a preliminary study. Medicine (Baltimore) 2015; 94:e882.
9.         Sonmez G, Basekim CC, Ozturk E, Gungor A, Kizilkaya E. Imaging of pulsatile tinnitus: a review of 74 patients. Clin Imaging 2007; 31:102-108.