"Diagnostic Imaging of an Oncology Patient" TUMOR TIDBITS, A BIWEEKLY VETERINARY ONCOLOGY E-LETTER Volume 2; Number 22; December 19, 2001. Editor: Kevin A. Hahn, DVM, PhD, Dipl - ACVIM (Oncology) & Overall Nice Guy! ANNOUNCEMENTS: Happy Holidays from the Doctors and Staff at Gulf Coast Veterinary Oncology! Don't forget to check our web site for the latest information at our Houston, Tomball and San Antonio locations! THIS WEEK'S TUMOR TIDBIT: DIAGNOSTIC IMAGING OF AN ONCOLOGY PATIENT As in human medicine, veterinary medicine has shown an increasing trend toward non-invasive procedures to diagnose many different types of the neoplasia, whether primary or metastatic. In response to this need and technologic advances, radiology has evolved to include many different forms of imaging in nuclear medicine, color flow and power doppler ultrasonography, and magnetic resonance imaging (MRI). PLAIN FILM SURVEY RADIOGRAPHY Despite new advances, plain film radiographs remain the standard. The radiograph is not intended to serve as a short cut diagnosis or take precedence over a thorough physical examination. It provides information about disease location, type, and extent; supplements findings from the database; and helps formulate and integrate treatment strategies. Radiographic nterpretation must be consistent and thorough. Procedurally, the clinician should: assess radiographic technical quality, check for artifacts, evaluate extrathoracic structures (spine, ribs, soft tissue), analyze thoracic organs and structures (trachea, heart, lungs), assess breed specific anatomic variations, and, correlate areas of concern/suspicion with the data base (including physical examination, ECG, clinical pathology, echocardiogram, and other imaging techniques). NUCLEAR MEDICINE Nuclear medicine techniques have been used extensively in humans to diagnose various forms of cancer. In fact, nuclear oncology is one of the most promising fields, as new, tumor-specific, radiopharmaceuticals are being introduced with increasing frequency. Veterinary nuclear medicine is being used clinically to help diagnose the presence of primary bony and soft tissue tumors, as well as in the staging of potential metastatic disease. The thyroid scan using either 99m TcO4 r 123I have been used to evaluate suspect thyroid adenocarcinomas in both dogs and cats. Although a thyroid scan cannot differentiate benign versus malignant disease, it is helpful as a screening tool. Benign hyperfunctional thyroid glands have round or oval shapes, homogeneous uptake with intense centers and tapering margins. “Hot nodulesEor dumbbell shaped glands are common, as is benign ectopic thyroid tissue. Glands that have irregular shapes, heterogeneous uptake with multiple photopenic areas and evidenc e of extension (invasi Bone scans are being used with increasing frequency to evaluate possible bony metastatic disease. Although the frequency of skeletal metastasis from primary bone tumor is low, the presence of metastatic disease may greatly alter the treatment plan or the owner decision to treat at all. The incidence of metastatic disease to bone from other types of tumors has not been evaluated extensively. It is known, however, that prostatic and mammary gland adenocarcinomas, as well as transitional cell carcinomas may metastasize to the bone. Bone scanning is the most sensitive and economical way to evaluate this possibility. Gallium (67 Ga) has been used in humans to detect local recurrences of primary soft tissue sarcomas, as well as defining the presence of regional metastasis. Tumor types evaluated in humans include leiomyosarcomas, mesotheliomas, schwannoma, rhabdomyosarcoma, fibrosarcoma, liposarcoma and synovial cell sarcoma. 67 Ga appears to be specific for active malignant sarcomatous tissue, and can differentiate benign fibrous (scar) tissue from active tumor tissue. In this regard, 67 Ga appears to diagnose primary soft tissue fibrosarcomas and demonstrate regional metastatic “skipElesions, therefore guiding the surgeon for more complete surgical removal, as well as diagnose early recurrence. The ptake in these tumors does not appear to be altered by previous radiation, chemotherapy, or soft tissue surgery. All sarcomatous tissue seen had marked, heterogeneous uptake, and mostly poorly defined margins. ULTRASONOGRAPHY Ultrasound has been used extensively to evaluate intrabdominal, intracardiac and heart base neoplasia. Similar to many forms of nuclear scintigraphy, ultrasound is very sensitive, but in many cases rather non-specific. Ultrasound is especially sensitive when there is nodular or multinodular disease, where the nodules have different acoustic properties than the surrounding tissue parenchyma. The sensitivity of ultrasound to diagnose diffuse diseases such as mast cell tumors or lymphosarcoma is much less. Ultrasound guided aspirates and true-cut biopsies have become the method of choice for obtaining tissue samples for cytologic or histologic diagnose. The advantages of ultrasound guided tissue sampling are many and include minimal morbidity, the ability to sample specific nodules and normal tissue, and the ability to sample nodules located deep within an organ. Disadvantages include limited tissue sample volumes. Color flow Doppler ultrasound has been investigated in many types of tumors to evaluate increased blood flow and abnormal arteriovenous shunting. Recently, an alternative to the display of frequency information with color flow Doppler imaging is to use a color map that displays the integrated power of the Doppler signal instead of its mean frequency shift. The result is that there is no aliasing. The image gives no information as regards to the direction of flow or velocity, and is much less angle dependent than frequency-based color flow imaging where noise from vessel wall movements may add to the displayed information. This form of Doppler is referred to as “Power DopplerE The resultant image permits higher effective gain settings for flow detection and increased sensitivity for flow detection, and is especially useful for evaluating “slow-flowE MAGNETIC RESONANCE IMAGING Magnetic resonance imaging is now commonly used to diagnose many forms of neoplasia that due to their location, are difficult to evaluate using other modalities. Examples include brain and brain stem neoplasia, spinal cord tumors, and adrenal tumors. MRI has shown to be helpful in demonstrating the size, shape, and amount of local tissue invasion. For nasal adenocarcinomas, it is much more sensitive than even high quality radiographs in evaluating the extent of disease. It has been shown to be superior to computed tomography (CT) in determining invasion into the rostral brain. It is also felt to be superior to CT in differentiating tumor tissue versus trapped fluid in the frontal sinus. CT, on the other hand is considered to be more sensitive than MRI in evaluating bony lysis secondary to tumor invasion. MR cannot differentiate between types of primary brain neoplasia, but based on the tumors location, amount of signal intensity on T1, T2, proton density and contrast enhanced T1 im ages, an educated gues WHAT DO WE DO AT GULF COAST? Well, the correct answer is whatever it takes to establish an appropriate diagnostic or therapeutic plan for the pet with cancer. There is a limit to the technology and it can be tumor type dependent. The basic approach is when in doubt, check it out. Don't hesitate to call or email us at Gulf Coast Veterinary Oncology! We can forward additional info by email if needed to our Radiologists. ALL THE BEST AND HAVE A GREAT HOLIDAY SEASON, Kevin A. Hahn, DVM, PhD Diplomate ACVIM (Oncology) & Overall Nice Guy Gulf Coast Veterinary Specialists 1111 West Loop South, Suite 150 Houston, TX 77027 P: 713.693.1166 F: 713.693.1167 http://www.gcvs.com mailto:drhahn@gulfcoastvetspec.com