Mass effect is the mechanical effect of a mass. For example, if you have a big benign tumor inside your chest, what effect does if have on your lungs' ability to do their job? If you have a big abscess near your esophagus, how does that affect your ability to swallow?
If you have a growing aneurysm inside your head then ....
You know an aneurysm dissects the layers of an artery, right? So if you have other, smaller arteries going off the one with an aneurysm developing, what happens to their blood supply? Suppose they're spinal perforators? Or the mesenteric artery? What are the effects from those being disrupted?
You probably know that atrial fibrillation puts a patient at risk for emboli, because the blood just kind of sits in the non-contracting atrium and can develop clots. What do you think might happen if there's blood pooling in an aneurysm?
When an aneurysm ruptures, what might the patient experience? Does it depend on where the aneurysm is? What might the nurse observe, depending on where it is?