Let's assume an adrenal tumor has been confirmed with either blood testing, imaging, or both. Two questions must be answered next:
- Is the tumor benign or malignant?
- Should you choose surgical treatment or medical management?
Benign vs. Malignant
While only approximately 15% of canine Cushing’s syndrome patients have adrenal tumors, half of them will have benign tumors and half will have malignant ones. The choice of therapy may well depend on which one the patient has.
If imaging has not yet been performed, this is the time to do so. Chest radiographs will be important as malignant adrenal tumors tend to spread to the chest. If such spread is seen, the tumor can be assumed to be malignant. Absence of such findings does not mean the tumor is benign. Ultrasound of the abdomen, if this has not already been done, (or even CT scanning, MRI imaging, or nuclear medicine scanning) will be needed to determine the size of the tumor, and to check for invasion of local abdominal tissues (especially in the liver).
Between evaluation of the chest and the abdomen, it may be possible to non-invasively determine if the tumor is malignant. It should be noted that the absence of tumor spread does not mean that the tumor is benign. If there is obvious spread to other organs, medical management is the only meaningful hope for the patient. Discuss with your veterinarian whether a referral to an oncologist for the most current medication plan is in your pet's best interest.
What if Imaging Fails to Confirm that the Tumor is Malignant?
As mentioned, it is not possible to say that the tumor is benign simply because tumor spread has not been detected. Still, no evidence of spread is about as close to determining that the tumor is benign as we can get without actually obtaining tissue samples. If the adrenal tumor is benign, there is an excellent chance for complete recovery if the tumor is surgically removed. The smaller the tumor, the easier the surgery, though the surgery involves delicate tissue in a difficult area.
What if Imaging Indicates the Tumor is Malignant?
If there is obvious tumor spread, surgery may be too risky. The decision to proceed with medical therapy will depend on how debilitated the patient is, and the degree of tumor spread versus the severity of the clinical signs of Cushing's disease. Relief, but not cure, of the clinical signs may be achieved by removing part of the tumor. Medical management with trilostane or with high doses of lysodren would be fair alternatives.
What you Should Know about Surgery
- Removing the adrenal gland is a relatively difficult surgery and may be best left to surgeons who perform this surgery with some regularity. (The adrenal gland is located between the aorta, which is the body's largest artery; the renal artery and vein, which are the sole blood supply to the kidney; and the phrenicoabdominal artery. This vascular area is half-jokingly referred to by surgeons as the Bermuda triangle. Surgery here is not for the inexperienced.) Removing an adrenal tumor is generally considered to be one of the most difficult surgeries in veterinary practice.
- Risk of bleeding is higher for larger tumors, especially if they are malignant and have invaded local structures. It is quite possible that the full extent of such invasion will not be apparent prior to surgery.
Animals with Cushing's syndrome have poor healing ability and tend to have high blood pressure. Several months of medical therapy (i.e., lysodren or trilostane) prior to surgery may be a good means to strengthen the patient, especially if the tumor is believed to be benign.
Illustration by Wendy Brooks, DVM
- The dog's natural cortisone mechanisms will have been suppressed by the tumor. This suppression means the patient will not be able to produce adrenal steroids on their own for a while and they will need to be given as medications. Several months of prednisone will likely be required at home. Some patients require florinef as an additional supplement. ACTH stimulation test are used to monitor the need for medication.
- Adrenal tissue is notoriously difficult for pathologists to grade as benign or malignant. It is possible that a tumor initially graded as benign will later turn out to be malignant.
- In a statistical survey of 63 dogs undergoing surgery for adrenal tumors:
- 6% (4) had inoperable tumors and were euthanized on the surgery table.
- 29% (18) died either in surgery or shortly thereafter due to complications.
The most common serious complication is thromboembolism (abnormal blood clots), which typically happens in the first 24 hours after surgery. This risk is tremendously reduced if the surgery can be performed by laparoscopy. Incisions are smaller, organ manipulation and bleeding is less and recovery is faster. Laparoscopy uses several small holes in the belly wall through which instruments, including a small video camera, can be inserted. Surgery takes place inside the belly and is viewed on a video screen or through a lens.
Laparoscopic surgical equipment. Photo courtesy of Wikipedia Commons.
Medical Therapy for the Adrenal Tumor
As can be seen from the above discussion, adrenalectomy is a high-risk surgery. It may not be a good choice for an elderly debilitated patient, especially if the tumor is large or has evidence of spread. Further, a 24-hour specialty center is usually needed for this sophisticated procedure and these centers may not be accessible, plus there is a great deal of expense involved in a surgical adventure of this magnitude. For these reasons, medical management may be selected as an alternative.
Lysodren is a chemotherapy drug that is able to erode the cortisol-producing layers of the adrenal gland. This ability has made lysodren the traditional medication for treating pituitary Cushing’s disease. It turns out the adrenal tumors will respond to higher doses as well. The higher doses needed to control adrenal tumors tend to produce more lysodren reactions than are seen when treating pituitary tumors. The average survival time for this type of therapy is 16 months.
Trilostane can also be used for functioning adrenal tumors though it will not actually diminish adrenal tissue (which could potentially diminish the tumor). Trilostane acts by inactivating excess steroid hormones and thereby managing the symptoms of Cushing's disease. You would think that this would not be effective since it does not directly affect the tumor, but at least one study showed a comparable survival time to that of patients on lysodren. As with lysodren, a protocol is needed that is different from those using the same drugs to treat pituitary-dependent Cushing's disease.