My father began prostate and bladder issues back 2013 and was treated for it by a urologist. 2day the doctor said he notice a small dot from the ultra sound on his bladder. what do you think could be the the causes of a dot from the the ultra sound?

Bladder tumor: ultra sound is minimally accurate to evaluate tumors.cystoscopy is better.Stones are easier to interpret.The finding may only be an innocuous fold in the bladder mucosa.Prostatic protrusion could also be an explanation.Cytology and cystoscopy with biopsy would be definitive.

Something or nothing: Urologist has likely advised cystoscopic examination to check bladder lining. Could be something benign or could be small early tumor which might respond to a minor cystoscopic resection. If so specimen would be examined by pathologist to provide accurate diagnosis. It could be suggestive of bladder stone If "dot" is echo dense & casts a "shadow".

Unreliable at times: A small dot as reported on US can be false positive, but requires a direct look into the bladder with cystoscope to confirm. Besides, it is useful to know every study has its own limit of specificity & sensitivity. How old is your father-I assumed around in his 50s? if so, all his problem likely results from aging-related impaired relaxation of urinary sphincter, i.e, bladder neck, prostate.