VETERINARY DIAGNOSTIC IMAGING
IMAGERIE DIAGNOSTIQUE VÉTÉRINAIRE
Robert Hylands
History and clinical signs
A 12-year-old, spayed female, Labrador retriever was referred to North Town Veterinary Hospital for spinal and abdominal computed tomography (CT) imag- ing and angiography. The dog had been tentatively diag- nosed by its regular veterinarian as having adrenal gland dependent hyperadrenocorticism. A previous ultrasono- graphic examination had demonstrated both adrenal glands to be enlarged, with the left one dramatically affected. She also had episodes of anxiety and hind end weakness, clinically supported by a wide base stance.
Clinically, the dog was polyuric/polydipsic and had episodes of heavy panting. Her complete blood (cell) count (CBC) indicated a mild anemia - red blood cell count 4 × 1012/L (reference range, 5.9 to 8.3 × 1012/L) and her biochemical profile demonstrated an elevation in both alkaline phosphatase (AP) 630 U/L (reference range, 18 to 94 U/L) and alanine aminotransferase (ALT) 99 U/L (reference range, 15 to 75 U/L) (Advance Vet Lab, Mississauga, Ontario). A low dose dexamethazone suppression test (LDDT) revealed no post-dexametha- zone cortisol depression at 2 h (460 nmol/L; reference
range, 0 to 30 mol/L) and 6 h (113 nmol/L) sampling (Advanced Vet Lab).
The retriever’s episodes of anxiety were considered to be the consequence of periods of hypertension, yet blood pressure measurements failed to confirm this. Scanning plain radiographs of the lumbar region outlined the dis- tribution of vertebral discospondylosis and calcification of disk material at lumbar vertebrae (L) 3-4 and L4-5. On a lateral radiographic view, a mild dorsal protrusion of mineralized disk material was suspected at the level of L4 and thought to be contributing to the dog’s hind end weakness. An iohexol (Omnipaque 350; Amersham Health, Oakville, Ontario) contrast enhanced abdominal spiral CT scan (Toshiba Express CT Scanner; Toshiba Medical Systems, Markham, Ontario) was performed to illustrate the 2 regions of interest. High-resolution images were obtained of both adrenal glands along with those of the caudal vena cava taken in the portal phase of con- trast enhancement (Figure 1). A 2nd series of 2-mm thickness views were taken parallel to and centered over the L4-5 disk space to confirm if the disk protrusion was clinically significant (Figure 2).
Colon
Vena Cava
Cranial Mesenteric artery
Blood in the vein
Rt Kidney
Dorsal Aorta
Rt Adrenal Carcinoma
Pheochromocytoma
DISC
Mild Protrusion
CHORD
Phęochromocytoma invading the Vena Cava
Adrenal Mass
Liver
VENA CAVA
What are your clinical diagnoses, differential diagnosis, and diagnostic plans?
Discussion
Our clinical diagnosis was malignant pheochromocytoma of the left adrenal gland invading the caudal vena cava, accompanied by a cortisol secreting adrenocortical car- cinoma of the right adrenal gland. Both tumors were clearly outlined and functionally differentiated by the distribution of the contrast material within in their paren- chyma. The functional characteristics of each neoplastic gland were later confirmed by histiological examination (Yager-Best Histovet, Guelph, Ontario) and showed a high correlation with the CT findings.
The smaller right adrenal carcinoma imaged predomi- nantly as a more homogeneous gland, whereas the large pheochromocytoma appeared as an irregularly shaped hyperdense tumor with multiple focal zones of low attenuation. These areas represented low iohexal uptake, giving the gland a very distinct mottled appearance.
The left tumor was effectively visualized by CT angiog- raphy to be invading the caudal vena cava and restricting its blood flow by approximately 60 % (Figures 1 and 3). The length of the infiltration into the vein craniad was approximately 4.5 cm, as measured by CT and later confirmed on post mortem (Figures 3 and 4). Both tumors also showed areas of mineralization within their parenchyma.
A color Doppler ultrasonographic (ATL Ultra Mark 9 HDI; Phillips Medical Systems, Markham, Ontario) examination was attempted prior to the CT scan in order to visualize any invasion of the caudal vena cava, but the results were inconclusive. Contrast enhanced CT has been reported to be very effective in differentiating pheochromocytomas (1). When such a tumor is sus- pected, care should be taken anytime any contrast agent is injected, as this can potentially precipitate a catechol-
Extension into the Vena Cava
Adrenal gland Pheochromocytoma
amine release, resulting in a hypertensive paroxysm. For this reason alone, in the future, magnetic resonance imaging (MRI), when available, may prove to be a safer diagnostic imaging alternative, since the use of an inject- able contrast agent is not usually needed in most, but not all, cases. In MRI, if the study is optimized for the inclu- sion of the adrenal glands, a fast spin echo sequence can outline a corticomedullary-like pattern, but a paramag- netic contrast agent must be used (2). This resolution is not possible with conventional spiral CT, but it may be with dynamic CT (5), where the scanner repeats and compares slices at the same location every 5 to 7 s over 5 min as the gland is being enhanced with an IV agent. By contrast, in some canine patients with pituitary dependent hyperadrenocorticism, dynamic CT has been the choice over MRI for the detection of microadenomas (3), because it can identify the enhancement of the neu- rophypophysis in a pituitary flush (4).
To distinguish whether the periods of hind end weak- ness were attributable to either the effects of a prolapsed disk, the irregular and spontaneous catecholamine release from the pheochromocytoma, or the pheochromocytoma in combination with the partial occlusion of the caudal vena cava, an axial CT scan over the suspect disk area was also performed (Figure 2). No evidence of any spinal chord compression was found on the 2-mm thick axial views. This lends further evidence that the dog’s entire list of clinical signs was the direct consequence of the independent secretions of both cortisol and cateco- lamines from the adenoma and pheochromocytoma, respectively.
The CT examination and diagnostic imaging resulted in an investigational exploratory examination being
delayed until a proper surgical plan could be tailored, so that we would be prepared for all potential complica- tions that could be incurred during the removal of the pheochromocytoma. Any attempt towards corrective surgery without prior knowledge of the relationship of the tumors with respect to the surrounding vascula- ture could increase the risk of a fatal outcome during the procedure. Advanced imaging techniques, such as spiral CT angiography or MRI, along with cross sec- tional and 3D reconstructions, are very useful tools that should be considered when attempting any such surgery.
References
1. Rosenstein DS. Diagnostic imaging in canine pheochromocytoma. Vet Radiol Ultrasound 2000;41:499-506.
2. Llabres-Diaz FJ, Dennis R. Magnetic resonance imaging of the presumed normal canine adrenal glands. Vet Radiol Ultrasound 2003;44:5-19.
3. van der Vlugt-Meijer RH, Voorhout G, Meij BP. Imaging of the pituitary gland in dogs with pituitary-dependent hyperadrenocorti- cism Mol Cell Endocrinol 2002;197:81-87.
4. van der Vlugt-Meijer RH, Meij BP, van den Ingh T SGAM, Rijnberk A, Voorhout G. Dynamic computed tomography of the pituitary gland in dogs with pituitary-dependent hyperadrenocorticism. J Vet Intern Med 2003;17:773-780.
5. Love NE, Fisher P, Hudson L. The computed tomographic enhance- ment pattern of the normal canine pituitary gland. Vet Radiol Ultrasound 2000;41:507-510.
BOOK REVIEW
COMPTE RENDU DE LIVRE
Bruce M. Pets, Professors, and Politicians: The found- ing and early years of the Atlantic Veterinary College. Island Studies Press, Atlantic Veterinary College, Charlottetown, Prince Edward Island, 2004, ISBN 0-919013-43-0. CDN $29.95.
T his book is an important addition to the literature on the history of veterinary education in Canada. While the founding and early history of the Ontario Veterinary College, the Western College of Veterinary Medicine, and la Faculté de Médecine Vétérinaire de L’Université de Montréal and its antecedents have been described in books by F.E. Gattinger, C.H. Bigland, and M. Pepin, respectively, no such book has been published on Canada’s newest veterinary college. The author, Marian Bruce, has a literary background mainly in journalism, and her book is written in a journalistic rather than schol- arly style, so is probably more readable as a result. The work has been thoroughly researched, with an extensive bibliography, which appeared to include the relevant sources. The author conducted over 70 interviews with individuals who were involved in the founding and early history of the College, and she is to be congratulated on conducting her research while this important resource was still available. More extensive endnotes would have better reflected the author’s research diligence.
The text is fairly evenly divided between the founding of the College and its post-foundation history up to 2004. The first 6 chapters cover the period from 1971, when the Canadian Agricultural Services Co-ordinating Committee indicated the need for a 4th veterinary college in Canada, to 1986, when the 1st class of DVM students was admitted. The trials and tribulations of this long gestation are described in almost painful detail. They were characterized by interprovincial wrangling and political, professional, and academic parochialism, and the final outcome was a credit to the determination of Reg Thomson, the planning co-ordinator of the project and eventual dean of the new college, to whom the book is dedicated, and to the University and Government of
Prince Edward Island. The negotiations were almost always acrimonious, and at times ludicrous, as when a federal minister proposed the Atlantic Veterinary and Aquamarine College as the colourful name for the new institution.
The final 5 chapters of the text trace the development of the new college from its foundation to the present day, and with the exception of some early academic problems as the University strove to accept its offspring, and the untimely retirement of its founding dean, this is a story of great accomplishment. Highlights include the maintenance of full accreditation, the development of the Veterinary Teaching Hospital and other services to the region, and the introduction of graduate programs as the faculty developed their research activities. Within a short time, the College was playing the kind of leader- ship role in veterinary medicine in Atlantic Canada that had been envisaged by its founders. Some details of the research projects of individual faculty members are included in an appendix, and the names of all graduates of the College up to 2004 are also recorded in appendi- ces, as are the names of medal winners, the department chairs, and tenure-stream faculty. Information on the curriculum is generally lacking. Several brief biogra- phies are interspersed with the text; these might be more readily accessible to the reader if they were included as an appendix, or at least listed in the Table of Contents. There are numerous black and white illustrations, which are well integrated in the text, as well as some color illustrations.
This book will be of interest to the graduates, faculty and staff of the Atlantic Veterinary College, to all who are interested in the history of higher education in Canada, and to veterinary historians. Its modest cost will make it readily available to a wide readership.
Reviewed by J. Brian Derbyshire, BSc, PhD, Professor Emeritus, Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2W1.