Comparison of the ability of computed tomography and magnetic resonance imaging to detect iliosacral metastasis of canine apocrine gland anal sac adenocarcinoma.

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The most common cancer of the perianal region arises from the apocrine glands associated with the anal sac. In many cases these tumors are found unexpectedly on a routine rectal examination. Anal sac tumors are often very large before they cause a detectable problem, such as perianal swelling, straining to defecate, licking at the perianal region, and bleeding. These tumors can invade the surrounding tissue and often spread to other organs (metastasize) early in the course of disease. 50-80% of these tumors will metastasize to the regional lymph nodes, typically the lumbar (also named medial iliac) lymph nodes, which are located on the inside of the abdominal cavity just below the lumbar vertebrae.

Staging tests then help to determine the extent of disease throughout the body as well as a dog's general health. These tests typically include blood work (a complete blood count and serum biochemical profile), urinalysis, thoracic x-rays, abdominal imaging (ultrasound, Ct or MRI) and aspirates of the regional lymph nodes. However, the best imaging modality to assess the lymph nodes is not known. The goal of this study is to compare ultrasound, CT and MRI for the ability to detect lymph node metastasis for apocrine gland anal sac adenocarcinoma.

Purpose:

The purpose of this study is to determine the best imaging modality (ultrasound, computed tomography, or magnetic resonance imaging) to detect lymph node metastasis (spread) in dogs that have apocrine gland anal sac adenocarcinoma (AGASACA).

Clinical Protocol: Clinical patients with perianal masses known or suspected to be AGASACA will be presented to the Kansas State University Veterinary Health Center. Fine needle aspiration of the mass will be performed if a diagnosis has not previously been confirmed. Initial diagnostics (i.e. CBC, chemistry, chest x-rays) will be performed If not completed within the past month. Upon confirmation of AGASACA, animals enrolled in the study will be placed under anesthesia.

While under anesthesia, three imaging techniques will be performed in a randomized order. An abdominal ultrasound will be performed by a board-certified radiologist. Computed tomography of the abdomen and pelvis will be performed in three steps. After an initial imaging study, 1-milliliter injections of a contrast agent will be injected in four spots surrounding the AGASACA. Repeated computed tomography scans of the pelvis and caudal abdomen will be performed at 1, 3, 5, and 10 minutes and, if needed, 25 min after injection. The purpose of these scans is to look for uptake of contrast into lymph nodes. The first node to uptake the contrast is referred to as the sentinel lymph node. After completing these scans, intravenous iodinated contrast will be injected at a dose of 2 ml/kg, and a final computed tomography study of the abdominal and pelvic cavities will be performed. Magnetic resonance imaging of the caudal abdomen and pelvic region will be obtained. During the study, gadolinium based IV contrast will be administered.

Immediately following completion of all three imaging modalities, one of the study investigators, a board-certified veterinary radiologist, will assess the images. Imaging characteristics will be used to determine if any lymph nodes are suspected to contain metastatic disease. Any lymph nodes that suspected to be metastatic based on any of the three imaging modalities will be sampled via ultrasound-guided fine needle aspirate and a cytologic diagnosis will be determined by a board certified veterinary clinical pathologist. In the case that no suspected-metastatic lymph nodes are observed on any of the three imaging modalities, the node identified as the sentinel node on computed tomography will be sampled via ultrasound guided fine needle aspirate.

Anesthetic and analgesic protocols will be at the discretion of the attending anesthesiologist and will be tailored specifically to each patient. Following anesthesia, the patient will be recovered. Based on the results of the imaging, the attending clinician will discuss treatment options. If surgery is elected, it will be performed the day after imaging or later. If lymph nodes are removed during the surgery, they will be submitted for histopathologic analysis.

Investigators:

David Upchurch, DVM, MS, DACVS
Alexis Watanabe, DVM
Nicolette Cassel, BVSc, MMedVet, DECVDI
Stacy McHaney, DVM, DACVR

Eligibility:

To be eligible for inclusion in this study each dog must be diagnosed and AGASACA via fine needle aspirate or biopsy either prior to arrival at Kansas State University or during the initial appointment. Dogs will be excluded from the study if they have had previous surgical removal of the primary mass. Other exclusion criteria will include prior surgery, pathologic conditions, or trauma that could affect lymph node drainage (e.g. pelvic trauma, prior iliosacral lymph node removal), any systemic illnesses that would prevent them from undergoing anesthesia or intravenous contrast administration (e.g. severe cardiovascular, renal, or respiratory disease), or any metallic implants that would preclude them from undergoing MRI

Risks:

While uncommon, there are risks to anesthesia in dogs. These include reactions to the anesthetic drugs, low blood pressure, aspiration pneumonia, and death. Close monitoring will be performed for the entirety of the sedation and during the immediate recovery period. Additionally, risks of contrast agent administration include damage to the kidneys or allergic reactions, although these complications are very rare.

Fees for Services:

Study funds will cover the cost of all three imaging techniques (ultrasound, computed tomography and Magnetic resonance imaging) as well as the cost of anesthesia during the imaging, contrast agents, and ultrasound-guided lymph node aspirates. The client will be responsible for any blood tests, cytology or thoracic imaging performed prior to study enrollment as well as the cost of surgery and surgery-related anesthesia charges.

Owner Responsibilities:

The owner will be responsible for following up with a re-check appointment in 2 weeks following surgery. This can be performed at the KSU VHC or with their primary care veterinarian. If performed with the primary care veterinarian, the contact information of the clinic should be made available to the study investigators.

For questions or concerns regarding this study, please contact either:

Alexis Watanabe
David Upchurch; (785)-532-5690