Tracheal diameter can be assessed from a thoracic radiograph, with assessment of tracheal diameter in dogs based on ratios between tracheal diameter and a skeletal measurement – however reference ranges are not available for the cat.  Tracheal narrowing may cause significant clinical problems, although tracheal hypoplasia in dogs may be clinically silent, and is rarely reported in cats (both mesati- and brachycephalic).  The tracheal diameter and trachea:thoracic inlet and trachea:rib ratios were calculated for populations of Domestic Short Haired (DSH) (n=68) and Persian (n=40) cats.  This gave reference ranges for radiographic tracheal measurements in these breeds. It is proposed that the tracheal diameter in a normal DSH cat should be 18% of the diameter of the thoracic inlet, and compared to 20% in Persian cats

Coleman, E.

Geary, M.

Gunn Moore, D.

Hammond, G.

Journal of Feline Medicine and Surgery

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Radiographic measurements of the trachea in domestic short haired and Persian cats

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       Hammond, G., Geary, M., Coleman, E., and Gunn Moore, D. (2011) Radiographic measurements of the trachea in domestic short haired and Persian cats. Journal of Feline Medicine and Surgery, 13 (12). pp. 881-884. ISSN 1098-612X http://eprints.gla.ac.uk/63667/  Deposited on: 9th May 2012   Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk Hammond et al Radiographic Measurements of the Trachea in Domestic Short Haired and Persian Cats 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46  Gawain Hammond MA VetMB MVM CertVDI DipECVDI FHEA MRCVS,  Mary Geary MVB BA MRCVS*ψ,  Erica Coleman BVM&S MRCVS*γ,  Danielle Gunn Moore* BSc BVM&S PhD FHEA MACVSc MRCVS  School of Veterinary Medicine, University of Glasgow, UK  *Royal (Dick) School of Veterinary Studies, Division of Veterinary Clinical Sciences, The University of Edinburgh, UK  γMs Coleman’s current address is Forest Veterinary Surgery, 10/12 Gregory Boulevard, Nottingham, UK.   ψMs Geary’s current address is Botanics Veterinary Hospital, 183 Botanic Road, Dublin, Ireland.                               1Tracheal Diameter in Persian Cats  47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 Radiographic Measurements of the Trachea in Domestic Short Haired and Persian Cats  Gawain Hammond, Mary Geary*Ψ, Erica Coleman*Ψ, Danielle Gunn Moore*  School of Veterinary Medicine, University of Glasgow, UK  *Royal (Dick) School of Veterinary Studies, Division of Veterinary Clinical Sciences, The University of Edinburgh, UK  ΨMs Coleman’s current address is Forest Veterinary Surgery, 10/12 Gregory Boulevard, Nottingham, UK.   Ms Geary’s current address is Botanics Veterinary Hospital, 183 Botanic Road, Dublin, Ireland. Abstract Tracheal diameter can be assessed from a thoracic radiograph, with assessment of tracheal diameter in dogs based on ratios between tracheal diameter and a skeletal measurement – however reference ranges are not available for the cat.  Tracheal narrowing may cause significant clinical problems, although tracheal hypoplasia in dogs may be clinically silent, and is rarely reported in cats (both mesati- and brachycephalic).  The tracheal diameter and trachea:thoracic inlet and trachea:rib ratios were calculated for populations of Domestic Short Haired (DSH) (n=68) and Persian (n=40) cats.  This gave reference ranges for radiographic tracheal measurements in these breeds. It is proposed that the tracheal diameter in a normal DSH cat should be 18% of the diameter of the thoracic inlet, and compared to 20% in Persian cats.  Introduction  Tracheal hypoplasia is an underdevelopment of the trachea resulting in a significantly narrowed tracheal diameter, which is commonly found in brachycephalic dog breeds, most notably the English Bulldog and Boxer1.  Changes that may be seen include close apposition or overlapping of the ends of the tracheal cartilage rings and absence of the dorsal tracheal membrane.  Hypoplastic tracheas have a stable diameter that does not vary with the phase of respiration1.  Tracheal hypoplasia may be regarded as a component of brachycephalic syndrome (along with stenotic nares, everted laryngeal saccules and an elongated soft palate)2.  Although the condition may frequently be clinically silent, the narrowing of the trachea may cause exacerbation of cardiovascular or respiratory disease1,2.  Clinical presentations and conditions associated with tracheal hypoplasia may include chronic coughing and recurrent tracheitis1.    In the cat dynamic tracheal collapse has been reported, both due to a congenital malformation of the tracheal cartilages3 and as an acquired condition associated with upper airway obstruction and neoplasms of the tracheal wall and  2Hammond et al lumen3,4,5,6,7.  Acquired narrowing of the tracheal lumen may be seen following trauma or associated with extraluminal compression or in association with thickening of the wall of the trachea93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 5,7.  However, tracheal hypoplasia has been seldom reported in cats, where it has been reported in association with mucopolysaccharoidosis8.   Diagnosis of tracheal narrowing (e.g. associated with collapse or hypoplasia is most easily made through radiography.  In dogs, the most commonly used technique is to calculate the ratio between the diameter of the trachea at the level of the thoracic inlet and the inner diameter of the thoracic inlet9.  In most dogs, this ratio will be greater than 0.2:1 – i.e. the tracheal diameter will be at least 20% of the diameter of the thoracic inlet.  In most brachycephalic breeds, this ratio has been calculated as normal if it is greater than 0.16:1, whilst in the English Bulldog, this measurement has been calculated to be normal for the breed if greater than 11% of the diameter of the thoracic inlet.  Other ratios that have also been described for assessing tracheal diameter in the dog include comparing the diameter of the mid-thoracic trachea to the width of the 3rd rib, with normal ratios of trachea:3rd rib being reported as >2.0 and >3.0, with tracheal hypoplasia being defined as a ratio of less than 1.010.  Although the diameter of the trachea can be assessed endoscopically, this technique is potentially hazardous due to the risk of obstruction of the already narrowed airway.  Radiographic assessment of the tracheal diameter and calculation of ratios to skeletal structures has not been reported in either Domestic Short Haired or Persian cats.  This study establishes reference ranges for these ratios in domestic short haired cats (DSH) and Persians, and investigates for differences in these ratios between the two breeds.  Materials and methods   The radiographic archives at the Small Animal Hospitals of the Royal (Dick) School of Veterinary Studies, University of Edinburgh and the Faculty of Veterinary Medicine, University of Glasgow were searched for thoracic radiographs of DSH and Persian cats and the associated medical records.  For inclusion in the study, the patients had to be at least one year old and to have no history of respiratory or cardiovascular disease, and had to have right lateral thoracic radiographs of good diagnostic quality, including the entire thorax and thoracic inlet in the collimated area, with the neck in a neutral position (i.e. not excessively hyperextended or flexed), with the forelimbs extended cranially and not superimposed on the thoracic cavity and with no axial rotation of the thorax.  Cases with radiographic evidence of thoracic disease were excluded.  In addition, cases with an endotracheal tube extending beyond the mid-cervical vertebrae were also excluded.  Once the films were collected, measurements (in millimetres) were taken from the films as follows (Figure 1): i) Tracheal diameter at the level of the thoracic inlet (TDinlet) – Figure 1a  3Tracheal Diameter in Persian Cats ii) Thoracic inlet diameter, from the dorsocranial aspect of the manubrium to the cranioventral aspect of the body of the 7139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 th cervical vertebra (TInlet) – Figure 1a iii) Tracheal diameter at the level of the 2nd intercostal space (TDintercostal) – Figure 1b iv) Width of the proximal third of the 3rd rib (Rib) – Figure 1b.  The means were calculated for each group of measurements.  Ratios were calculated between: i) TDinlet divided by TInlet (Measurement points from Figure 1a) ii) TDintercostal divided by Rib (Measurement points from Figure 1b)  The mean measurements and ratios were compared between the populations (DSH and Persians) using a two-tailed t-test.  Results  Radiographs from 68 DSH and 40 Persians were included in the study.  The majority had undergone thoracic radiography for either oncological staging or investigation of systemic disease.  Measurements were subjectively simple to obtain using a standard ruler.  The mean measurements are presented in table 1. The mean ratios and p-values are presented in table 2.  There was no significant difference in the mean tracheal diameter at either the thoracic inlet or intercostal space locations, nor in the width of the 3rd rib between the two populations.  However there was a significant difference in the measurements of the thoracic inlet, with the Persian cat population showing a significantly narrowed thoracic inlet compared to the DSH population.  There was a significant difference in both of the ratios calculated, with the Persian population showing significantly greater Trachea:Thoracic Inlet and Trachea:3rd Rib ratios than the DSH population.    Discussion   Given the potential significance of tracheal hypoplasia or other causes of tracheal narrowing, coupled with the lack of reference ranges for normal radiographic tracheal measurements in the cat, the authors felt it valuable to establish reference ranges for the trachea in mesaticephalic (DSH) and brachycephalic (Persian) cat breeds.  When comparing the absolute size of the trachea between the DSH and Persian populations, there was no significant difference between the mean tracheal diameters (Table 1).  However, when the trachea:thoracic inlet are compared, that of the Persian population are significantly greater than that of the DSH population. This is believed to be due to a proportional dorsoventral  4Hammond et al 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 compression of the thoracic inlet of the Persian cat when compared to that of the DSH (demonstrated by the significant difference in absolute measurements of the thoracic inlet shown in Table 1).  This anatomic conformational difference is likely of no clinical significance, but results in the alteration in the trachea:thoracic ratio, and should be considered when assessing other structures using the thoracic skeletal structure as a comparison (e.g. the height of the cardiac silhouette) as this apparent flattening could result in a misinterpretation of the structure or organ in question.  The authors propose that the trachea in a DSH should be considered of normal diameter if it is 18% of the diameter of the thoracic inlet, and that of the Persian cat should be considered normal if it is 20% of the thoracic inlet.  The trachea:rib ratios demonstrated a similar (although less significant) variation between the populations.  Given the similarity in absolute size of the tracheas, this is most suggestive of thicker ribs in the DSH population demonstrated by the absolute measurements (although this was not statistically significant).  Although the weights and sizes of the patients included in the study was not always available, subjectively there was no significant discrepancy in body size between the two populations of adult cats (skeletally immature cats were excluded from the study) and so this is not thought to be an influence on the skeletal measurements.  However, it was felt that the trachea:thoracic inlet ratio was considerably easier to obtain, and it would be the authors’ advice that the trachea:thoracic ratio is used for assessing trachea diameter in preference to the trachea:rib ratio.   In addition, given the fairly uniform nature of the body sizes in the study population, it may be argued that a tracheal diameter of around 5.5mm is normal for a cat (DSH or Persian) of average size, and this would forego the requirement to calculate a ratio with a set skeletal measurement.  However, it cannot be guaranteed that the body sizes of the study population are typical of the population as a whole, and in addition some cats will lie at the extremes of the population range.  It is therefore the authors’ recommendation that the tracheal diameter is assessed using a ratio with a  skeletal measurement (such as those described above) as this should minimise variations due to absolute body size. Tracheal hypoplasia in the dog is frequently clinically silent, but as it can significantly worsen the clinical effect of a respiratory disorder such as pneumonia prior knowledge of its presence in a patient can be valuable1.  Detection is most commonly through thoracic radiography, although computed tomography or endoscopy may also be indicative of tracheal hypoplasia1,11.  On the basis of the results of the study, it can be shown that there was no evidence of clinically silent tracheal hypoplasia in the population of Persian cats studied.  It is possible that tracheal hypoplasia does exist in the Persian cat, but always results in clinically significant respiratory disease (and as a result, such cases would have been excluded from the population used in this study). However, this is thought unlikely by the authors, considering the frequently silent nature of tracheal hypoplasia in the dog.  This would suggest that the brachycephalic anatomic changes seen in Persian cats are restricted to the skull and upper respiratory tract, such as the nasopharyngeal turbinates reported to be seen in  5Tracheal Diameter in Persian Cats about 20% of brachycephalic cats11.  There is the question of whether the study population of Persian cats was truly representative of the population as a whole – unfortunately, in part due to this being a retrospective study, the possibility of a skewed population cannot be excluded.  However, the authors feel that the wide range of presentations, and the inclusion of cases from two different referral hospitals reduces this possibility. 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275  In conclusion, this study establishes reference ranges for the assessment of tracheal diameter in Persian and Domestic Short Hair Cats: for DSH cats with no evidence of cardiorespiratory disease, the tracheal diameter should be 18% of the internal diameter of the thoracic inlet, and this measurement should increase to 20% in normal Persian cats.  References  1. Coyne BE, Fingland RB.  Hypoplasia of the trachea in dogs: 103 cases (1974-1990).  Journal of the American Veterinary Medical Association 201:768-72, 1992. 2. Rieks TW, Birchard SJ, Stephens JA.  Surgical correction of brachycephalic syndrome in dogs: 62 Cases (1991-2004).  Journal of the American Veterinary Medical Association 230:1324-1328, 2007.  3. Hendricks JC, O’Brien JA.  Tracheal collapse in two cats.  Journal of the American Veterinary Medical Association 187:418-419, 1985.  4. Fujita M, Miura H, Yasuda D, Hasegawa D, Orima H.  Tracheal narrowing secondary to airway obstruction in two cats.  Journal of Small Animal Practice 45:29-31, 2004.  5. Kim DY, Kim JR, Taylor HW, Lee YS.  Primary extranodal lymphosarcoma of the trachea in a cat.  Journal of Veterinary Medical Science 58:703-706, 1996.  6. Mims HL, Hancock RB, Leib MS, Waldron DR.  Primary Tracheal Collapse in a cat.  Journal of the American Animal Hospital Association 44:149-153, 2008.  7. Bell R, Philbey AW, Martineau H, Nielsen L, Pawson P, Dukes-McEwan J.  Dynamic tracheal collapse associated with disseminated histiocytic sarcoma in a cat.  Journal of Small Animal Practice 47:461-464, 2006.  8. Schultheiss PC, Gardner SA, Owens JM, Wenger DA, Thrall MA.  Mucopolysaccharidosis VII in a cat.  Veterinary Pathology 37:502-505, 2000.  9. Harvey CE, Fink EA.  Tracheal diameter, analysis of radiographic measurements in brachycephalic and non-brachycephalic dogs.  Journal of the American Animal Hospital Association 18:570-576, 1982.   6Hammond et al 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 10. Suter PF.  A text atlas of thoracic diseases of the dog and cat.  Wettswil, Switzerland: Peter Suter, 1984:238-240.  11. Schlueter C, Budras KD, Ludewig E, Mayhofer E, Koenig HE, Walter A, Oechtering GU.  CT and anatomical study of the relationship between head confirmation and the nasolacrimal drainage system.  Journal of Feline Medicine and Surgery 11:891-900, 2009.    Figure Legend:   Figure 1a: Lateral feline thoracic radiograph showing measurement points for Trachea:Thoracic Inlet Ratio:  * = Level to measure tracheal diameter (mm) at thoracic inlet (TDInlet);                = Thoracic inlet diameter  (mm) (TInlet).    Figure 1b: Lateral feline thoracic radiograph showing measurement points for Trachea:3rd Rib Ratio: * = Point to measure tracheal diameter (mm) in 2nd intercostal space (TDIntercostal); ►◄ = Point to measure width of proximal ⅓ of 3rd rib (mm) (between arrow heads) (Rib).   Table Legends:   Table 1: Mean measurements and p-values for DSH and Persian study populations  Table 2: Mean Ratios and p values for DSH and Persian study populations.   7Mean Measurements   DSH Persian P value Trachea –Thoracic Inlet  5.4mm 5.6mm 0.37 Trachea –  Mid-Thoracic 5.4mm 5.6mm 0.42 Thoracic Inlet 32.5mm 28.7mm <0.005 Proximal 3rd Rib 3.5mm 3.3mm 0.05 Table 1: Mean measurements and p-values for DSH and Persian study populations  Mean Ratios   DSH Persian P value Trachea:Thoracic Inlet 0.18 (Range 0.13-0.23) 0.20 (Range 0.13-0.28) <0.005 Trachea:3rd Rib 1.59 (Range 1.20-2.33) 1.71 (Range 1.25-2.33) <0.05 Table 2: Mean Ratios and p values for DSH and Persian study populations.  

A text atlas of thoracic diseases of the dog and cat. Wettswil, Switzerland: Peter Suter,

CT and anatomical study of the relationship between head confirmation and the nasolacrimal drainage system.

Dynamic tracheal collapse associated with disseminated histiocytic sarcoma in a cat.

Hypoplasia of the trachea in dogs: 103 cases

Mucopolysaccharidosis VII in a cat. Veterinary Pathology 37:502-505,

Primary extranodal lymphosarcoma of the trachea in a cat.

Primary Tracheal Collapse in a cat.

Surgical correction of brachycephalic syndrome in dogs: 62 Cases

Tracheal collapse in two cats.

Tracheal diameter, analysis of radiographic measurements in brachycephalic and non-brachycephalic dogs.

Tracheal narrowing secondary to airway obstruction in two cats.

 Tracheal diameter can be assessed from a thoracic radiograph, with assessment of tracheal diameter in dogs based on ratios between tracheal diameter and a skeletal measurement. Reference intervals are not, however, available for the cat. Tracheal narrowing may cause significant clinical problems, although tracheal hypoplasia in dogs may be clinically silent, and is rarely reported in cats (both mesati- and brachycephalic). The tracheal diameter and trachea:thoracic inlet and trachea:rib ratios were calculated for populations of domestic shorthair (DSH) ( n = 68) and Persian ( n = 40) cats. This gave reference intervals for radiographic tracheal measurements in these breeds. It is proposed that the tracheal diameter in a normal DSH cat should be 18% of the diameter of the thoracic inlet, and compared to 20% in Persian cats. </jats:p

Radiographic measurements of the trachea in domestic short haired and Persian cats

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