Angiomyolipoma is a benign tumor, and when asymptomatic and with diameter of 4 cm, doesn't require treatment.
As your doctor has told you, you'll be followed up with ultrasound or other imagining techniques, to see if the tumor is growing larger than 4 cm.
Treatment will be indicate if the tumor grows larger, causes some complications like bleeding, or, if the doctor can't exclude the malignancy (possible cancerous nature).

How can the doctor tell if this tumor is benign or cancer ??? I have been told they are just going to watch the tumor currently and I need to have another ultrasound in 6 months. My worry is that cancer runs in my family and I have lost family members because of it. I am scared to just sit back and just wait and see if it grows. How do I know it is not cancer. I do not want to sit back, wait, and then find out I have stage 4 cancer.
Thanks for you assistants on helping me learn about this tumor I have !!!

I was just diagnosed with the same type of tumor (mine is only 5mm). My doctor wasn't forthcoming with information (other than get another ultrasound in 6 months) but I can tell you what I have discovered online. In ultrasound imagery, different types of materials show up either lighter or darker. Objects with a higher fat content, for example, tend to show up as lighter in color. I'm assuming the doctor who read your ultrasound determined, based on the how the image of your tumor appeared on the screen, that the content of the tumor was consistent with a benign tumor, rather than cancer. There are also probably differences in shape, etc., between a angiomyolipoma and a cancerous tumor. From what I've read, these types of tumors can be successfully identified via ultrasound without additional testing.

I will say, however, that from what I've read that tumors larger than 4 cm or ones that have resulted in symptoms (I'm assuming that if they thought you had a gallbladder problem it was because you were experiencing discomfort) are more likely to be removed. This isn't because they are cancerous or will turn cancerous this is in order to eliminate the pain (if it is bothering you enough to want to go through surgery). Also, larger tumors of this type could hemorrhage. Nothing life threatening in that, either, but apparently something to consider. If you're concerned, you could always go for a second opinion (particularly if you wait a while and you're still experiencing pain).

I hope that helps. Good luck and I hope you're feeling better, soon!

I have to say. I had a angiomyolipoma of my R-kidney. All the scans, ultrasounds, Ct's, Mri's and even blood tests all said I had renal cell carcinoma! they removed my whole kidney and only after pathology did they say it was non cancerous angiomyolipoma. So I have to diagree on the scanning results in my case (showing it was cancer because of the darkness and they found no fat content on any of the scans.) However, they had said because of the location of the tumor they would have had to remove my kidney anyway. You want to make sure your tumor is not near any large veins or artieries where it can cause a rupture orcausing clots. As a matter of fact, they were so sure that I had cancer that they did not want to biposy it for fear of pulling cancer cells to other parts of the body. You need an MRI to show exact location and if it interferes with any other structures, veins/arteries. They also told me that the odd's of getting another tumor are nill. It is 4 years later and another tumor in my L-kidney. Good Luck to you and make sure you cover all your bases, if your not happy and content with what your Dr tell's you then seek a second, third or 4th opinion. I had 3 seperate opinions and they all said cancer and they were all wrong.