We all know healthcare is expensive in the Unites States. Most of us have paid a medical bill, wondering why the cost of that seemingly small procedure is so high. But what are the most expensive surgeries? Here's a list of the top ten most expensive medical procedures according to a 2008 Millman report and citizenreviewonline.org, along with the reasons why they cost so much:

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1. Intestine Transplant
Cost: $1,121,800

A transplant of the intestine is done to replace dead intestinal tissue with live tissue from a donor, often because of disease or the presence of a tumor. Because intestinal disease is sometimes accompanied by liver failure, intestine transplants can be done in conjunction with a liver transplant, adding more than $180,000 to the bill.

2. Heart Transplant
Cost: $787,700

Heart transplants are among the most complicated of procedures, carrying great risk. Waiting lists are long, and preparation for the surgery is lengthy and expensive. Add to this the expensive procurement of the organ, and you can see why the cost is so great.

3. Bone Marrow Transplant
Cost: $676,800 Allogeneic ($300,400 for Autologous)

Bone marrow transplants can be done with a donor's marrow (allogeneic) or your own bone marrow (autologous), costing much less. Finding a donor for a bone marrow transplant is difficult, and complications after the procedure are very common. Add to this the risky nature of the procedure, the lengthy prep time in the hospital as well as an extensive recovery period, and you have a cocktail for a hefty medical bill.

4. Lung Transplant
Cost: $657,800 double ($450,400 for single)

When other therapies don't work, lung transplants are a last resort for patients of lung disease like emphysema and cystic fibrosis. As with other transplant surgeries, wait lists are long and cost is high because of the lengthy hospital stay.

5. Liver Transplant
Cost: $523,400

As with a heart transplant, liver transplants are high risk and high cost, with an accompanying waiting list. Criteria are high, which means administrative and prep procedure costs add to the bottom line.

6. Open Heart Surgery
Cost: $324,000

With heart disease as the leading cause of death in the U.S. at 26%, open heart surgery is a more common procedure than may be expected. Part of the high cost of open heart surgery is because it's often an urgent medical procedure that is usually followed by complications. Longer care and follow-up needed after surgery add to the price tag.

7. Pancreas Transplant
Cost: $275,500

Transplants of the pancreas are usually needed when a patient has type 1 diabetes or renal failure. It is often done in tandem with a kidney transplant, almost doubling the cost of the surgeries at $439,000.

8. Kidney Transplant
Cost: $259,000

Kidney transplants, like the other transplants on this list, are expensive due to the risk, recovery and prep expense. The one difference is that with kidney transplants, the old kidney isn't removed because it's been shown it reduces risk that way; surgeons find a different blood supply to attach the new kidney to.

9. Tracheotomy
Cost: $205,000

A tracheotomy involves making an incision in the neck to allow the patient to breathe, either permanently or temporarily. Since this is often an emergency room procedure, costs are high. After care is extensive, adding to the bill.

10. Destruction of Lesion of Retina
Cost: $153,000

When lesions on a retina (this is part of the eye), also called retinoblastoma, are removed, the risks are great as with the above-mentioned procedures. This procedure is pricey because of the precision skills required for this procedure, the lengthy recovery and follow-up.

Bottom Line
If you think these costs are high, consider that patients with a chronic disease affecting more than one organ often need multiple organ transplants, with bills exceeding a million dollars. Why the whopping price tags for all these surgeries? In cases of transplants, the hospital stay before and after the surgery makes up about 75 percent of the bill. Some of the cost comes from liability insurance, those high premiums hospitals and doctors have to pay to cover themselves in case of lawsuits. A side-effect of the large amount of liability lawsuits is that doctors often order more (expensive) tests than needed to cover themselves, a practice called defensive medicine.

Lack of insurance among more than 47 million Americans drives costs up, since the uninsured use emergency rooms, and often when they've waited so long that pricey emergency surgery is the only option. Add this to the high cost of medication and medical equipment, and you can see how these price tags balloon. The bottom line: health insurance coverage is vital if you need one of these life-threatening and extremely expensive procedures. (Learn what your options are in Fighting The High Costs Of Healthcare and Buying Private Health Insurance.)