Cervical venous hum is a continuous murmur heard over the internal jugular veins. It is thought to be produced by the partial compression of the internal jugular vein by the transverse process of the atlas as well by the effect of gravity. It is more common on the right side because the right internal jugular vein and brachiocephalic vein has straight access to the superior vena cava so that the flow velocity is higher on the right side. The cervical venous hum is obliterated by manual compression of the internal jugular vein, Valsalva manoeuvre and the supine position. On the contrary, it increases on assuming the upright posture and during inspiration. The cervical venous hum is louder in diastole due to the rapid atrial filling. Cervical venous hum is a fairly common finding in children. Conditions causing hyperkinetic circulation like anemia, pregnancy and thyrotoxicosis may make the venous hum more prominent. The venous hum has a plateau shape in systole and a crescendo-decrescendo shape in diastole. It is better heard in the right supraclavicular fossa, with the bell of the stethoscope and the patient looking to the left side. Intensity will decrease if the person turns his chin towards the side of auscultation. Cervical venous hum is the most common continuous murmur.
Though most cases of cervical venous hum are not due to any significant pathology, rare cases of cervical venous hum due to intracranial A-V malformation have also been described [Hardison JE. Cervical venous hum: A clue to the diagnosis of intracranial arteriovenous malformation. NEJM. 1968; 278:587; Cartlidge NE et al. Intracranial A-V malformation associated with cranial bruit and cervical venous hum. Postgrad Med J. 1970;46:726-8]. In these cases, the hum was audible even in the supine position.
An interesting case of surgical treatment of cervical venous hum has also been reported [Brennan FJ, Salerno TA. Surgical treatment of symptomatic cervical venous hum. J Thorac Cardiovasc Surg. 1981;81:135-6]. This patient had pulsating tinnitus in the right ear and a venous hum heard over the right internal jugular vein. The tinnitus was abolished by manoeuvres which abolished the venous hum. Ligation of right internal jugular vein was done resulting in permanent symptomatic relief.