Pulsatile tinnitus usually beats in cadence with the heart.  It is caused by the sound of blood flowing through vessels.   There are many causes, most are benign but still may need treatment.  

There are four categories of causes:

1)  Arterial Sounds
2)  Venous Sounds
3)  Benign or Malignant Tumors
4)  Spasm of Middle Ear Muscles

Diagnosis of the cause of pulsatile tinnitus involves the imaging of the vascular system of the head and neck. 

To the right, is a video of a CT angiogram which visualizes the arterial vascular system of the head and neck (this is an old video and one would probably consider MRI angiographic as an alternative test).  Other tests which may be ordered are carotid ultrasound, MRI angiography and standard angiography.

A carotid ultrasound can test for carotid plaques which can cause pulsatile tinnitus and if obstructive or friable may cause a stroke.  However, it does not evaluate the siphon portion of the internal carotid artery or the intracranial vessels.  CT angiograms are non-invasive tests but donot delineate the arterial system as well as standard angiography.  Both use iodine as a contrast agent plus the CT angiogram uses ionizing radiation.   MRI angiography can give very good pictures of the vascular system but has a slight increase in error as compared to standard angiography but the pictures many not be of the same quality.  The use of contrast (gadolinium) can help improve pictures quality but in rare patients, it can be toxic to the kidneys.   Standard angiography is an invasive test that has a small but real risk of complications.  Angiograms of the carotid artery have been reported to have a 1% to 2% chance of a stroke - View Reference.

These tests may find vascular malformations and vascular tumors, such as a glomus tympanicum or jugulari.  Glomus tumors or paraganglioms are a type of vascular tumor.  They are usually benign but may rarely be malignant.   The angiogram shown on the right demonstrates a small glomus tumor in the middle ear cavity. 

View Video
 

Increase venous flow can cause a vascular hum.  This is due to noisy blood flow through the internal jugular vein, the large vein which delivers blood from the brain to the heart.   The loudness of a hum can vary with different head positions and may be stopped by placing light pressure on the neck.

Increased intracranial pressure or normal pressure hydrocephalus can cause a venous hum.   Normal pressure hydrocephalus usually occurs in individuals over the age of 60.  It is a very slow and mild increase in the pressure of the cerebral spinal fluid which can over time cause dilatation of the ventricles and dementia.  

Anatomical abnormalities such as a jugular bulb which is dehiscent into the middle ear can cause pulsatile tinnitus.  Below is a 48 year old patient patient with a jugular diverticulum which caused pulsatile tinnitus. 
  

  
Middle ear infections and fluid can also cause pulsatile tinnitus by increasing middle ear blood flow. 

Spasms and contraction of middle ear muscles such as the tensor tympani muscle can cause a type of tinnitus which does not beat with the heart.  This contraction moves the eardrum and the patient can usually feels the motion and finds it annoying.