Page 184 - Feline diagnostic imaging

186 11 Advanced Imaging Modalities
11.3.2 Bronchitis of increased lung opacities secondary to the primary neo-
plastic process [19,30].
Computed tomography is more accurate in evaluation of
lower airway disease, with more accurate assessment of
thickened bronchi and bronchiectasis compared to tho- 11.3.5 Mediastinal Disease
racic radiographs in the cat [19]. Bronchial walls can be Normal thoracic lymph nodes (cranial mediastinal, trache-
measured easily, with affected principal bronchial wall obronchial, and sternal) are barely visible on CT imaging.
thickness of 1.2–1.7 mm, compared to 0.8–0.9 mm in unaf- Enlargement is variably identified, and better visualized
fected cats. Peripheral bronchial wall thickness in cats with after contrast administration [16,17,19,20,31]. When
lower airway inflammation measured 0.9–1.2 mm [19]. enlarged, the lymph nodes are rounded, homogeneous soft
The same peripheral bronchial walls could not be identi- tissue opacities. Enlarged tracheobronchial lymph nodes
fied in unaffected cats. Additional findings seen on CT but may result in compression, ventral and lateral deviation of
not on thoracic radiographs in cats with lower airway the caudal mainstem bronchi (Figure 11.14d). Both sternal
inflammation include bronchiectasis, pneumonia, and and cranial mediastinal lymphadenopathy can create a
mainstem bronchial and tracheal wall thickening with cranioventral mediastinal mass, with elevation of the cra-
luminal stenosis [19]. Thickened bronchial walls, collapse nial thoracic trachea and widening of the cranial mediasti-
of the right middle lung lobe, hyperinflation, and rib frac- num on dorsal reconstructions.
tures are visualized with greater detail and clarity on CT Thoracic radiographs can be inadequate in the diagnosis
[19,20].
of mediastinal masses, especially in the presence of pleural
effusion. CT is superior in locating mass lesions to the
11.3.3 Pneumonia mediastinum, determining the character (cystic versus
solid) and extent of disease, including regional vascular
Computed tomography features of pneumonia include soft invasion (Figures 11.15 and 11.16) [17]. This is critical
tissue opacification, either as a patchy alveolar pattern or information for determination of surgical resectability of a
more solid consolidation with ventral distribution [19,20]. mass. CT angiography is necessary to more reliably evalu-
Peribronchial thickening in allergic and parasitic infec- ate vascular invasion. Routine contrast‐enhanced CT
tions, perivascular thickening in parasitic vascular infec- appears to be insensitive in the detection of vascular inva-
tions, associated hilar lymphadenopathy, especially in sion [31]. Mediastinal neoplasia, such as thymoma, lym-
fungal pneumonia, and nodule/mass formation due to phoma, ectopic thyroid tumor or carcinoma, has a variable
abscess and granuloma formation are all CT features of appearance depending on the origin of the tumor [17].
pulmonary inflammation [15–17,19,20,23–28].
11.3.6 Pleural Space
11.3.4 Neoplasia
The two pleural layers (visceral and parietal) are seen as a
Computed tomography is extremely valuable in evalua- combined opaque line, together with the innermost layer of
tion of neoplastic disease, determining the exact location, intercostal muscles at the periphery of the lung surface [20].
extent, and involvement of adjacent structures (chest Individual interlobar fissure lines are not visualized on CT
wall, pleura, bronchi, vessels, lymph nodes). The CT scans of normal cats unless perpendicular to the scan plane.
appearance of feline pulmonary neoplasia is variable, and The presence of pleural effusion is not a limitation to
includes soft tissue mass, often with mineralization or visualization of cardiac and mediastinal structures, unlike
central necrotic nonenhancing area, and deviation/com- plain radiographs. The inherently better contrast resolu-
pression of adjacent bronchi and vessels (Figure 11.14a– tion of CT allows differentiation of fluid and soft tissue
c) [16,19,20,29]. Masses may be restricted to one lobe or rather than the border effacement created by pleural effu-
disseminated. The margins are often poorly defined and sion radiographically. For this reason, CT can be used to
irregular. Enlarged tracheobronchial lymph nodes are evaluate the chest wall, lungs, and mediastinum to better
identified inconsistently, but are better visualized with determine a cause of the pleural effusion [19,20,32,33]. The
contrast enhancement. Neoplastic masses enhance rela- patient can be repositioned in the CT gantry so that pleural
tively consistently. Feline bronchial neoplasia may be dif- fluid does not surround the diseased area. Despite the
fuse, with areas of alveolar consolidation, bronchial greater contrast, soft tissue lesions are still better evaluated
thickening, interstitial infiltrates, and mineralization when surrounded by radiolucent lung (Figure 11.17).
[16,19,20,29]. Pulmonary metastasis in cats is generally Pleural fluid usually has a CT number similar to water,
less well defined than in dogs [20]. It is more likely to be although hemorrhagic effusions are often higher (>50 HU)
detected on CT than thoracic radiographs, often because [20]. Most pleural effusions are bilateral, but exudative or