During a TCD exam via the transtemporal window, an antegrade signal is noted at a depth of 50mm. Which vessel is most likely being examined?

In a transcranial Doppler (TCD) exam, the transtemporal window allows for access to several critical intracranial vessels. When an antegrade signal is detected at a depth of 50 mm, it is most commonly associated with the middle cerebral artery.

The middle cerebral artery, which branches from the internal carotid artery, is typically located at an approximate depth of 50 to 60 mm when accessed through the transtemporal window. Antegrade flow in this artery indicates that blood is moving in a forward direction toward the brain, consistent with normal physiological conditions.

Other vessels located at different depths or with varying flow directions through TCD make them less likely candidates. For example, the anterior cerebral artery generally resides deeper than the middle cerebral artery, while the posterior cerebral artery is usually accessed through the suboccipital or transforaminal approaches. Similarly, the internal carotid artery is primarily assessed using extracranial Doppler imaging, as it does not provide signals through the transtemporal window.

Thus, the antegrade signal at a depth of 50 mm strongly indicates the middle cerebral artery as the vessel being evaluated.