Cystitis usually indicates an infection or inflammatory process of the bladder. Infectious cystitis that is treated with antibiotics is usually diagnosed using an analysis of your urine. There are other causes of cystitis which are inflammatory, like after certain chemotherapy or radiation treatments.
On CT scan, the bladder can sometimes look thickened. This can be a real thickening of the wall, or a thickening because the bladder is not fully filled. It can be difficult to tell in some cases when the bladder is not fully filled. The radiologist will therefore describe it as a finding but leave it up to the clinical doctor to determine whether it is clinically significant by writing: correlate clinically.
This means that the significance of the imaging finding should be correlated with clinical and laboratory findings. For example, a 20 year old women with lower urinary symptoms, pain and fever may well have cystitis and this can be confirmed with an analysis of the urine.
A 70 year old man who has bladder wall thickening and no symptoms referable to the urinary tract may have a thickened bladder wall from a big prostate. A big prostate may partially block the flow of urine from the bladder and cause the bladder muscle to thicken.
A 35 year old man who has an appendicitis in the emergency room has a thickened bladder wall. But the radiologist notes that this may simply be the result of incomplete filling of the bladder. He alerts the emergency physician to correlate clinically. That is, see whether that finding could represent cystitis based on his clinical symptoms and analysis of the urine.
By mentioning bladder wall thickening and stating correlate clinically, the radiologist is alerting the referring physician that something is wrong on imaging. He is telling the clinical physician that he should make sure this finding truly represents an abnormality based on the patient’s clinical presentation. The physician should treat the patient and not an imaging finding. Imaging is just one additional piece of information.