ttp://www.bsava.com
EDITORIAL
Diagnostic imaging for chronic nasal disease in dogs The diagnosis of chronic nasal disease is frequently challenging. The methods commonly used to obtain a definitive diagnosis, such as conventional radiography and rhinoscopy, have proven to be less than reliable (Sullivan 1987, Thrall et al. 1989, Tasker et al. 1999). The complexity of the canine nose and overlying bony structures is such that radiography does not reliably offer the detailed information necessary to determine a precise cause for chronic nasal disease. It is well recognised that radiographs have poor sensitivity for differentiating inflammatory rhinitis from neoplasia and fungal rhinosinusitis. Rhinoscopy provides limited information about the extent of disease and in many situations the presence of copious mucopurulent or haemorrhagic discharge prevents adequate visualisation of the nasal cavity. With the expanding availability of advanced imaging modalities over the last 25 or so years, a wealth of understanding of and enhanced ability to achieve a diagnosis for chronic nasal disease in dogs has come about. Computed tomography (CT) and magnetic resonance imaging (MRI) are now considered the diagnostic imaging modalities of choice for evaluation of chronic nasal disease. Nasal CT and MRI have proven to be superior to conventional radiography for precise evaluation of diseases within the nasal cavity, paranasal sinuses, periorbital region, tympanic bulla and skull. Both modalities excel in determining the extent and severity of the disease process present. Much of the earlier veterinary literature regarding advanced diagnostic imaging of the canine nose was centred on studies in dogs with nasal neoplasia. Comparison studies of CT and radiography in dogs with nasal neoplasia (Thrall et al. 1989, Park et al. 1992) were shortly followed by comparison of MRI and radiography in dogs with nasal neoplasia (Petite & Dennis 2006). These studies demonstrated the superiority of advanced imaging modalities over radiography in determining the extent and extension of neoplasms within the nasal cavity, frontal sinuses, orbital region and major airway passages. This added information is critical to assist in tumour staging, providing a prognosis, planning of treatment and possible treatment-related complications. Studies comparing the diagnostic differences between CT and MRI for evaluation of canine nasal neoplasia have also been reported (Dhaliwal et al. 2004, Drees et al. 2009). Neither of these studies demonstrated superiority of one advanced diagnostic imaging modality over the other. There is a slight advantage in CT detecting lysis of bones, with MRI providing more detailed information of soft tissue structures. Studies utilising advanced diagnostic imaging describing the changes associated with non-neoplastic disease have largely been confined to CT (Burk 1992, Saunders et al. 2003, Lefebvre et al. 2005). Inflammatory canine nasal diseases are important, as they represent approximately 55% of chronic nasal diseases in dogs (Kuehn et al. 2013). These studies have advanced our understanding of inflammatory nasal disease with imaging patterns that lean towards a specific diagnosis or limited list of Journal of Small Animal Practice
•
Vol 55
•
July 2014
•
rule-outs based on the CT findings. CT is extremely effective, but not absolute, in discriminating between dogs having fungal rhinosinusitis, idiopathic rhinosinusitis and nasal neoplasia (Kuehn 2014). Few single diagnostic investigations are infallible, and CT is no exception. For example, chronic intranasal foreign bodies can be associated with severe focal to extensive turbinate atrophy mimicking those changes associated with fungal rhinitis, and nasal polyps may have diagnostic imaging findings similar to those observed with malignant nasal neoplasia. It is of interest that in the current issue of Journal of Small Animal Practice (Furtado et al. 2014) a study is finally reported utilising MRI to describe the changes seen in dogs with inflammatory nasal disease rather than nasal neoplasia. Although the MRI findings in this study of dogs with sinonasal aspergillosis and idiopathic rhinosinusitis mirror those seen with CT, it does demonstrate that MRI is as useful as CT in lending a probable diagnosis based on the images provided. One aspect of this study that is particularly interesting, and may confer an advantage to MRI over CT, is that dogs with sinonasal aspergillosis on T1-weighted images often had turbinate hyperintensity compared to muscle, whereas those with idiopathic rhinosinusitis were associated with turbinate hypointensity or isointensity compared to muscle. Tissues not related to fat on a T1-weighted image (before the administration of gadolinium) having hyperintensity would suggest a paramagnetic substance being present (Gavin 2009). Iron and manganese are the principal paramagnetic substances within the body and with manganese being present only in small quantities, iron would be the element present. Dogs with sinonasal aspergillosis have widespread areas of turbinate necrosis and haemorrhage, whereas this is not a common feature in dogs with idiopathic rhinosinusitis. Perhaps degradation of haemoglobin to methaemoglobin in areas of mucosal turbinate necrosis and haemorrhage in dogs with sinonasal aspergillosis accounts for this finding. Further studies will certainly be needed to determine if turbinate hyperintensity on T1-weighted images is constantly identified in dogs with sinonasal aspergillosis. If so, this may lend an advantage to MRI over CT to help differentiate dogs having sinonasal aspergillosis from those with severe idiopathic rhinosinusitis with concomitant turbinate destruction present. From my current perspective, there does not seem to be superiority of MRI over CT for diagnostic evaluation of chronic nasal disease in dogs. Each modality has its own subtle strengths and weaknesses. One point that I believe CT has an advantage is that bone lysis is easier to identify, which is critical for treatment decisions should breach of the cribriform plate be present in patients with sinonasal aspergillosis. Over time MRI has become increasingly available in academic and private referral veterinary hospitals. Costs associated with MRI are considerable when compared with CT, although lesser for low-field veterinary MRI units. Image acquisition time is much more rapid with CT than with MRI, which greatly reduces anaesthetic time for the patient
© 2014 British Small Animal Veterinary Association
341
Editorial
undergoing evaluation. Even though I have both advanced diagnostic imaging modalities in my hospital, the lack of a consistent advantage of MRI over CT and the faster acquisition time for CT are major reasons I will typically use CT in the evaluation of dogs with chronic nasal disease. Additional studies ascribing the diagnostic value of MRI in dogs with inflammatory nasal disease and comparison studies utilising MRI and CT are very much needed. References Burk, R. L. (1992) Computed tomographic imaging of nasal disease in 100 dogs. Veterinary Radiology & Ultrasound 33, 177-180 Dhaliwal, R. S., Kitchell, B. E., Losonsky, J. M., et al. (2004) Subjective evaluation of computed tomography and magnetic resonance imaging for detecting intracalvarial changes in canine nasal neoplasia. International Journal of Applied Research in Veterinary Medicine 2, 201-208 Drees, R., Forrest, L. J. & Chappell, R. (2009) Comparison of computed tomography and magnetic resonance imaging for the evaluation of canine intranasal neoplasia. Journal of Small Animal Practice 50, 334-340 Furtado, A. R. R., Caine, A. & Herrtage, M. E. (2014) Diagnostic value of MRI in dogs with inflammatory nasal disease. Journal of Small Animal Practice 55, 359-363 Gavin, P. R. (2009) Sequence selection. In: Practical Small Animal MRI. Eds P. R. Gavin and R. S. Bagley. Wiley-Blackwell, Ames, IA, USA. pp 8-9 Kuehn, N. F. (2014) Rhinitis in the dog. In: Kirk’s Current Veterinary Therapy XV. Eds J. Bonagura and D. Twedt. Elsevier Saunders, St. Louis, MO, USA. pp 635-643
Kuehn, N. F., Teichner, S. & Rose, M. (2013) Clinical diagnosis after advanced diagnostic imaging in 185 dogs with chronic rhinitis (7 year retrospective study). Research Communication ECVIM-SA Congress, Liverpool, UK Lefebvre, J., Kuehn, N. F. & Wortinger, A. (2005) Computed tomography as an aid in the diagnosis of chronic nasal disease in dogs. Journal of Small Animal Practice 46, 280-285 Park, R. D., Beck, E. R. & LeCouteur, R. A. (1992) Comparison of computed tomography and radiography for detecting changes induced by malignant nasal neoplasia in dogs. Journal of the American Veterinary Medical Association 201, 1720-1724 Petite, A. F. B. & Dennis, R. (2006) Comparison of radiography and magnetic resonance imaging for evaluating the extent of nasal neoplasia in dogs. Journal of Small Animal Practice 47, 529-536 Saunders, J. H., Van Bree, H., Gielen, I., et al. (2003) Diagnostic value of computed tomography in dogs with chronic nasal disease. Veterinary Radiology & Ultrasound 44, 409-413 Sullivan, M. (1987) Rhinoscopy: a diagnostic aid? Journal of Small Animal Practice 28, 839-843 Tasker, S., Knottenbelt, C. M., Munro, E. A., et al. (1999) Aetiology and diagnosis of persistent nasal disease in the dog: a retrospective study of 42 cases. Journal of Small Animal Practice 40, 473-478 Thrall, D. E., Robertson, I. A., McLeod, D. A., et al. (1989) A comparison of radiographic and computed tomographic findings in 31 dogs with malignant nasal cavity tumors. Veterinary Radiology 30, 59-65
Ned F. Kuehn, DVM, MS, DACVIM (SAIM) BluePearl Veterinary Partners - Michigan Southfield, MI 48034, USA
Ned F. Kuehn graduated with a DVM degree from Michigan State University (USA) in 1983. Following a year internship in small animal medicine and surgery at Louisiana State University, he then completed a 3-year residency in small animal internal medicine and a MS degree in Clinical Sciences at Purdue University. He thereafter achieved board certification by the American College of Veterinary Internal Medicine in Small Animal Internal Medicine. Following a short period as an Assistant Professor in Internal Medicine at the College of Veterinary Medicine at Mississippi State University he entered private practice in 1989. Currently, he is Medical Director and Internal Medicine Residency Program Director for BluePearl Veterinary Partners – Michigan. He has authored over 50 scientific publications, research abstracts and book chapters. His area of clinical research interest is nasal disease of the dog and cat.
342
Journal of Small Animal Practice
•
Vol 55
•
July 2014
•
© 2014 British Small Animal Veterinary Association
EDITORIAL
Diagnostic imaging for chronic nasal disease in dogs The diagnosis of chronic nasal disease is frequently challenging. The methods commonly used to obtain a definitive diagnosis, such as conventional radiography and rhinoscopy, have proven to be less than reliable (Sullivan 1987, Thrall et al. 1989, Tasker et al. 1999). The complexity of the canine nose and overlying bony structures is such that radiography does not reliably offer the detailed information necessary to determine a precise cause for chronic nasal disease. It is well recognised that radiographs have poor sensitivity for differentiating inflammatory rhinitis from neoplasia and fungal rhinosinusitis. Rhinoscopy provides limited information about the extent of disease and in many situations the presence of copious mucopurulent or haemorrhagic discharge prevents adequate visualisation of the nasal cavity. With the expanding availability of advanced imaging modalities over the last 25 or so years, a wealth of understanding of and enhanced ability to achieve a diagnosis for chronic nasal disease in dogs has come about. Computed tomography (CT) and magnetic resonance imaging (MRI) are now considered the diagnostic imaging modalities of choice for evaluation of chronic nasal disease. Nasal CT and MRI have proven to be superior to conventional radiography for precise evaluation of diseases within the nasal cavity, paranasal sinuses, periorbital region, tympanic bulla and skull. Both modalities excel in determining the extent and severity of the disease process present. Much of the earlier veterinary literature regarding advanced diagnostic imaging of the canine nose was centred on studies in dogs with nasal neoplasia. Comparison studies of CT and radiography in dogs with nasal neoplasia (Thrall et al. 1989, Park et al. 1992) were shortly followed by comparison of MRI and radiography in dogs with nasal neoplasia (Petite & Dennis 2006). These studies demonstrated the superiority of advanced imaging modalities over radiography in determining the extent and extension of neoplasms within the nasal cavity, frontal sinuses, orbital region and major airway passages. This added information is critical to assist in tumour staging, providing a prognosis, planning of treatment and possible treatment-related complications. Studies comparing the diagnostic differences between CT and MRI for evaluation of canine nasal neoplasia have also been reported (Dhaliwal et al. 2004, Drees et al. 2009). Neither of these studies demonstrated superiority of one advanced diagnostic imaging modality over the other. There is a slight advantage in CT detecting lysis of bones, with MRI providing more detailed information of soft tissue structures. Studies utilising advanced diagnostic imaging describing the changes associated with non-neoplastic disease have largely been confined to CT (Burk 1992, Saunders et al. 2003, Lefebvre et al. 2005). Inflammatory canine nasal diseases are important, as they represent approximately 55% of chronic nasal diseases in dogs (Kuehn et al. 2013). These studies have advanced our understanding of inflammatory nasal disease with imaging patterns that lean towards a specific diagnosis or limited list of Journal of Small Animal Practice
•
Vol 55
•
July 2014
•
rule-outs based on the CT findings. CT is extremely effective, but not absolute, in discriminating between dogs having fungal rhinosinusitis, idiopathic rhinosinusitis and nasal neoplasia (Kuehn 2014). Few single diagnostic investigations are infallible, and CT is no exception. For example, chronic intranasal foreign bodies can be associated with severe focal to extensive turbinate atrophy mimicking those changes associated with fungal rhinitis, and nasal polyps may have diagnostic imaging findings similar to those observed with malignant nasal neoplasia. It is of interest that in the current issue of Journal of Small Animal Practice (Furtado et al. 2014) a study is finally reported utilising MRI to describe the changes seen in dogs with inflammatory nasal disease rather than nasal neoplasia. Although the MRI findings in this study of dogs with sinonasal aspergillosis and idiopathic rhinosinusitis mirror those seen with CT, it does demonstrate that MRI is as useful as CT in lending a probable diagnosis based on the images provided. One aspect of this study that is particularly interesting, and may confer an advantage to MRI over CT, is that dogs with sinonasal aspergillosis on T1-weighted images often had turbinate hyperintensity compared to muscle, whereas those with idiopathic rhinosinusitis were associated with turbinate hypointensity or isointensity compared to muscle. Tissues not related to fat on a T1-weighted image (before the administration of gadolinium) having hyperintensity would suggest a paramagnetic substance being present (Gavin 2009). Iron and manganese are the principal paramagnetic substances within the body and with manganese being present only in small quantities, iron would be the element present. Dogs with sinonasal aspergillosis have widespread areas of turbinate necrosis and haemorrhage, whereas this is not a common feature in dogs with idiopathic rhinosinusitis. Perhaps degradation of haemoglobin to methaemoglobin in areas of mucosal turbinate necrosis and haemorrhage in dogs with sinonasal aspergillosis accounts for this finding. Further studies will certainly be needed to determine if turbinate hyperintensity on T1-weighted images is constantly identified in dogs with sinonasal aspergillosis. If so, this may lend an advantage to MRI over CT to help differentiate dogs having sinonasal aspergillosis from those with severe idiopathic rhinosinusitis with concomitant turbinate destruction present. From my current perspective, there does not seem to be superiority of MRI over CT for diagnostic evaluation of chronic nasal disease in dogs. Each modality has its own subtle strengths and weaknesses. One point that I believe CT has an advantage is that bone lysis is easier to identify, which is critical for treatment decisions should breach of the cribriform plate be present in patients with sinonasal aspergillosis. Over time MRI has become increasingly available in academic and private referral veterinary hospitals. Costs associated with MRI are considerable when compared with CT, although lesser for low-field veterinary MRI units. Image acquisition time is much more rapid with CT than with MRI, which greatly reduces anaesthetic time for the patient
© 2014 British Small Animal Veterinary Association
341
Editorial
undergoing evaluation. Even though I have both advanced diagnostic imaging modalities in my hospital, the lack of a consistent advantage of MRI over CT and the faster acquisition time for CT are major reasons I will typically use CT in the evaluation of dogs with chronic nasal disease. Additional studies ascribing the diagnostic value of MRI in dogs with inflammatory nasal disease and comparison studies utilising MRI and CT are very much needed. References Burk, R. L. (1992) Computed tomographic imaging of nasal disease in 100 dogs. Veterinary Radiology & Ultrasound 33, 177-180 Dhaliwal, R. S., Kitchell, B. E., Losonsky, J. M., et al. (2004) Subjective evaluation of computed tomography and magnetic resonance imaging for detecting intracalvarial changes in canine nasal neoplasia. International Journal of Applied Research in Veterinary Medicine 2, 201-208 Drees, R., Forrest, L. J. & Chappell, R. (2009) Comparison of computed tomography and magnetic resonance imaging for the evaluation of canine intranasal neoplasia. Journal of Small Animal Practice 50, 334-340 Furtado, A. R. R., Caine, A. & Herrtage, M. E. (2014) Diagnostic value of MRI in dogs with inflammatory nasal disease. Journal of Small Animal Practice 55, 359-363 Gavin, P. R. (2009) Sequence selection. In: Practical Small Animal MRI. Eds P. R. Gavin and R. S. Bagley. Wiley-Blackwell, Ames, IA, USA. pp 8-9 Kuehn, N. F. (2014) Rhinitis in the dog. In: Kirk’s Current Veterinary Therapy XV. Eds J. Bonagura and D. Twedt. Elsevier Saunders, St. Louis, MO, USA. pp 635-643
Kuehn, N. F., Teichner, S. & Rose, M. (2013) Clinical diagnosis after advanced diagnostic imaging in 185 dogs with chronic rhinitis (7 year retrospective study). Research Communication ECVIM-SA Congress, Liverpool, UK Lefebvre, J., Kuehn, N. F. & Wortinger, A. (2005) Computed tomography as an aid in the diagnosis of chronic nasal disease in dogs. Journal of Small Animal Practice 46, 280-285 Park, R. D., Beck, E. R. & LeCouteur, R. A. (1992) Comparison of computed tomography and radiography for detecting changes induced by malignant nasal neoplasia in dogs. Journal of the American Veterinary Medical Association 201, 1720-1724 Petite, A. F. B. & Dennis, R. (2006) Comparison of radiography and magnetic resonance imaging for evaluating the extent of nasal neoplasia in dogs. Journal of Small Animal Practice 47, 529-536 Saunders, J. H., Van Bree, H., Gielen, I., et al. (2003) Diagnostic value of computed tomography in dogs with chronic nasal disease. Veterinary Radiology & Ultrasound 44, 409-413 Sullivan, M. (1987) Rhinoscopy: a diagnostic aid? Journal of Small Animal Practice 28, 839-843 Tasker, S., Knottenbelt, C. M., Munro, E. A., et al. (1999) Aetiology and diagnosis of persistent nasal disease in the dog: a retrospective study of 42 cases. Journal of Small Animal Practice 40, 473-478 Thrall, D. E., Robertson, I. A., McLeod, D. A., et al. (1989) A comparison of radiographic and computed tomographic findings in 31 dogs with malignant nasal cavity tumors. Veterinary Radiology 30, 59-65
Ned F. Kuehn, DVM, MS, DACVIM (SAIM) BluePearl Veterinary Partners - Michigan Southfield, MI 48034, USA
Ned F. Kuehn graduated with a DVM degree from Michigan State University (USA) in 1983. Following a year internship in small animal medicine and surgery at Louisiana State University, he then completed a 3-year residency in small animal internal medicine and a MS degree in Clinical Sciences at Purdue University. He thereafter achieved board certification by the American College of Veterinary Internal Medicine in Small Animal Internal Medicine. Following a short period as an Assistant Professor in Internal Medicine at the College of Veterinary Medicine at Mississippi State University he entered private practice in 1989. Currently, he is Medical Director and Internal Medicine Residency Program Director for BluePearl Veterinary Partners – Michigan. He has authored over 50 scientific publications, research abstracts and book chapters. His area of clinical research interest is nasal disease of the dog and cat.
342
Journal of Small Animal Practice
•
Vol 55
•
July 2014
•
© 2014 British Small Animal Veterinary Association
