Usually not. A head CT done without contrast given into a vein in most cases will not identify an aneurysm. Rarely, a large aneurysm may be seen as a mass, but we won’t know it’s an aneurysm for sure just with a head CT. Smaller aneurysms will not be seen because the blood vessels of the brain are not shown well on a head CT.
A brain aneurysm is best detected using a special test of the blood vessels of the brain called an angiogram. This can be a CT or MRI angiogram. A head CT is best at showing a bleed inside the brain. It also shows masses, shift of structures from a mass or edema. CT is also good at showing the ventricular system and any enlargement. A head CT may show a stroke which is past the early stage.
A head CT is a good start at evaluating symptoms referred to the head. It is especially good at determining whether something needs urgent attention. It does not show aneurysms or many other conditions which may be responsible for neurological symptoms. An MRI of the brain is best for that.
A head CT is good for showing a bleed related to a ruptured aneurysm called a subarachnoid bleed. This will be seen as bright density hemorrhage in the subarachnoid space of the brain. In some cases, your doctor will need to do a lumbar puncture to diagnose a ruptured aneurysm.
If there is a bleed into the subarachnoid space, than a special imaging test called an angiogram will be ordered to look for aneurysm. Sometimes this is ordered initially when the doctor suspects an aneurysm or complications. The angiogram is good at showing the major arteries and it’s branches. Even tiny aneurysms are sometimes seen on these tests.
A head CT therefore will not show most aneurysms. A head CT done without contrast given into the vein is a great test to detect urgent conditions but not an aneurysm. It can show the bleed from a ruptured aneurysm. Further testing with an angiogram of the blood vessels will be needed to look for an aneurysm.