Pharynx, Larynx and Thorax


Figure 720 Lateral projection of pharynx and larynx.

1 Mandibular bodies

2 Temporomandibular joints

3 Tympanic bullae of temporal bones

4 External acoustic meatus of temporal bone

5 Petrous temporal bone

6 Occipital condyle

A Atlas

B Axis

C 3rd cervical vertebra

D Stylohyoid bones

E Epihyoid bones

F Ceratohyoid bones

G Basihyoid bone

H Thyrohyoid bones

7 Soft palate

8 Epiglottis

9 Cranial limit of laryngeal part of pharynx

10 Caudal limit of laryngeal part of pharynx. Caudal limit is the caudal border of the cricoid cartilage.

11 Caudal limit of larynx

12 Position of the rostral cornu of thyroid cartilage

13 Rostral limit of the arytenoid cartilage. The orniculate process of the arytenoid cartilage is missing in the cat.

14 Vestibular fold

15 Glottic cleft. The cat lacks lateral ventricles and has instead shallow depressions.

16 Infraglottic cavity

17 Trachea

18 Oesophagus

19 Nasopharynx

20 Oropharynx

21 Intrapharyngeal ostium

22 Laryngeal vestibule

23 Thyropharyngeal muscle

24 Cricopharyngeal muscle

Thorax: Figures 721744

Cardiovascular system: Figures 721727

Right lateral recumbent and dorsoventral projections with schematic drawings

Figure 721 Projection to focus on the cardiovascular system. Right lateral recumbent projection of thorax. Radiograph taken during general anaesthesia with inflation of lung lobes. British Domestic Short Haired cat 6 years old, neutered male (same cat as left lateral recumbent projection of thorax, Figure 733). (Approximately 90% of original size.)

Figure 722 Right lateral recumbent projection of thorax to focus on the cardiovascular system.

Pericardium and heart

Cranial border

1 Right auricle

2 Right ventricle

In this projection the aortic arch is not visible but a large aortic arch is more commonly seen in the cat than the dog. It appears as a distinct bulge at the cranial border, at or below the right auricle level, extending into the cranial mediastinum. Where the aortic arch covers the cranial waist the cardiac shadow appears cranially tilted with an increase in sternal contact.

Caudal border

3 Left atrium

4 Left ventricle

Although the cat has a cranial and caudal waistline, as in the dog, using these as a guideline for cardiac enlargement is not as straightforward, particularly for the caudal waistline. Separation of left atrium and left ventricle is more difficult and enlargements often do not affect the waistline.

5 Base

6 Apex

Fat accumulation within the pericardial sac is only occasionally seen in the cat but care must be taken to differentiate between soft tissue and fat opacities. In this radiograph fat opacity is visible outside the pericardium on the ventral thoracic cavity wall (7).

The right lateral recumbency is preferred for the cardiac shadow, as discussed in the dog section. In addition the projection should be at full inflation of the lung lobes.

This film is not as fully inflated as the left lateral recumbent projection of thorax of the same cat, Figure 733. As such the vascular shadows are more prominent and the cardiac shadow is slightly cranially tilted. However craniocaudal and dorsoventral cardiac measurements for both projections are the same.

Right lateral recumbent projection, with drawing, and left lateral recumbent projection of thoracic cavity in forced inflation, or over-inflation, of lung lobes, Figures 728730, have been included to show the effect of ‘loss’ of pulmonary radiographic opacity and ‘upright’ cardiac shadow caused by hyperinflation.


8 Thoracic aorta. (Aortic arch is not clearly seen as a separate structure in this radiograph.)

9 Ventral limit of cranial vena cava

10 Caudal vena cava

11 Cranial lobe artery

12 Cranial lobe vein

The radiolucent shadow between the paired cranial vessels is the lumen of the cranial lobe bronchus. It should not be mistaken for an air bronchogram. An air bronchogram is a characteristic radiographic feature of an alveolar pattern. The latter occurs in diseases which cause an infiltration into the alveoli. Soft tissue opacity replaces the alveolar air lucency. This results in adjacent air-filled lumens of the bronchi becoming visible.

Bronchial walls are not generally visible in the cat unless they are diseased.

13 Pulmonary artery and veins

The arrangement of pulmonary veins is different in the cat compared to the dog. In the dog the veins are symmetrically arranged as left and right sets of lobar veins.

In the cat there are three groups draining: the two parts of the left cranial lobe; the middle and cranial lobes of the right side; and caudal lobes of right and left lungs. Each of these groups is of two or three veins and they are not symmetrically arranged. Hence radiographic differentiation of veins in the cat is very difficult.

Non-cardiovascular structures

14 Tracheal lumen

14(a) Endotracheal tube

15 Tracheal walls

16 Cranial mediastinum

17 Ventral mediastinum. (See juvenile section, Figure 742, for appearance in kittens when the thymus occupies the entire cranioventral mediastinum at a level ventral to cranial vena cava. It also extends 1 to 2 cm cranial to the 1st ribs into the neck.)

18 Diaphragmatic shadow

18(a) Right ‘crus’

18(b) Left ‘crus’

18(c) Cupola

In this radiograph the appearance of the right and left ‘crura’ would suggest left rather than right recumbency. Identification of lateral recumbency is more difficult in the cat than the dog. Often ‘crura’ are superimposed and, as in this radiograph, are misleading.

Entry of the caudal vena cava is usually unhelpful leaving only the gastric gas, caudal to the left ‘crura’, as a guide for recumbency analysis. In this radiograph insufficient gas was present to show the presence of the gastric fundus caudal to the left ‘crura’.

19 Caudal border of scapula

20 Humerus

21 Manubrium of sternum

22 Xiphoid process

23 2nd thoracic vertebra

24 11th thoracic vertebra

25 Mineralised costal cartilages

26 Skin and muscle masses of forelimbs


It is widely reported that the cat has a fairly standard shape and size for its cardiac shadow, compared to the breed variation seen in dogs.

With this assumption radiographically normal thoracic projections, from clinically normal cats with no evidence of cardiac abnormalities, should have been relatively easy to obtain (see ‘Normality’ in the Introduction). This was not the case as many cats were found to have cardiac ‘enlargements’ from their radiographic shadows.

Guidance drawing on normal cardiac size: Figure 723

Figure 723 Drawing of right lateral recumbent projection of thorax to provide guidance on normal cardiac size.

A Apicobasilar length at tracheal bifurcation

B Maximum width between cranial and caudal borders of heart at right angles to A

C Distance between the cranial border of 5th rib and caudal border of 7th rib

D 5th rib

E 7th rib

F Cranial endplate of body of 4th thoracic vertebra.

Figure 724 Schematic drawing of right lateral recumbent projection of thorax to illustrate cardiac chambers and major vessels (corresponds to drawing Figure 722, but with the exclusion of some thoracic cavity details seen in radiograph).

Left side with associated vessels

a Left atrium with pulmonary veins (1)

b Left auricle

c Left ventricle (drawing does not indicate wall thickness)

d Aorta with left subclavian artery (2) and brachiocephalic trunk (3). Aortic arch forms the most cranial structure of the ‘heart and major vessels’.

e Left atrioventricular valve; mitral. Length is usually about 25% the craniocaudal width of the heart.

f Aortic valve

Right side with associated vessels

g Right atrium with cranial vena cava (4) and caudal vena cava (5) and azygos vein (6)

h Right auricle. Right auricle is in contact with aortic arch and almost forms the cranial border of the ‘heart’ mass at the cardiac base.

i Right ventricle (drawing does not indicate wall thickness)

j Pulmonary trunk; main pulmonary artery or pulmonary artery segment

k Right atrioventricular valve; tricuspid. Length is usually about 50% of the craniocaudal width of the heart. It overlaps both aorta and pulmonary artery.

l Pulmonary valve

Figure 725 Projection to focus on cardiovascular system. Dorsoventral projection of thorax. Radiograph taken during general anaesthesia with inflation of lung lobes. British Domestic Short Haired cat 4 years old, neutered male. (Approximately 140% of original size.)

Guidance information on normal cranial mediastinal size: Figure 726

Figure 726 Dorsoventral projection of thorax to focus on cardiovascular system.

Pericardium and heart

Right side

1 Right atrium

2 Right ventricle

Left side

3 Left auricle

4 Left ventricle

5 Apex. Formed by left ventricle.


6 Aortic arch. In young cats the aortic arch is often obscured by thymic tissue while in aged cats this structure may become enlarged and distorted (see Figure 732).

7 Aorta

8 Pulmonary trunk; main pulmonary artery

9 Level of cranial vena cava within cranial mediastinum soft tissue opacity

10 Level of caudal vena cava. (The vein is is not seen as a separate shadow in this film.)

11 Artery to caudal lung lobe

12 Vein to caudal lung lobe

13 Artery to cranial lung lobe

14 Vein to cranial lung lobe. A linear radiolucent shadow has been created between the artery and vein (14a). As in the right lateral recumbent projection of thorax, Figure 721, the lucent shadow must not be mistaken for an air bronchogram. (Air bronchograms appear in disease as a characteristic radiographic feature of an alveolar pattern.)

Non-cardiovascular structures

15 Tracheal lumen

16 Tracheal wall

Guidance on normal size of cranial mediastinum

Width should be less than the width of the thoracic vertebral body.

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Jun 23, 2017 | Posted by in ANIMAL RADIOLOGY | Comments Off on Pharynx, Larynx and Thorax
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