Page 213 - BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery, 2nd Edition

BSAVA Manual of Canine and Feline Head, Neck and Thoracic Surgery

Ventrodorsal
16.6 thoracic
radiograph of the same cat
VetBooks.ir as in Figure 16.5. Again, the
mass effect of the neoplasm
is resulting in distortion of
heart and trachea have been
Cranial adjacent structures. The
mediastinum displaced to the right with
loss of the typical cardiac
silhouette. A large soft
tissue structure occupies the
Thymic mid-thorax.
shadow
(‘sail’)

Ventrodorsal thoracic radiograph of a young dog. The thymus
16.4
is clearly visible as a triangular structure in the cranial
mid-thorax. Note the width of the cranial mediastinum in comparison
with the caudal mediastinum on this view.
notch, using the heart as an acoustic window. Trans-
oesophageal transducers can be used to acquire images of
defects are present in the trachea or mainstem bronchi. As the heart base and major vessels within the mediastinum. In
previously mentioned, concurrent subcutaneous emphy- the investigation of cranial mediastinal masses, ultrasono-
sema may develop in such animals. graphy can provide useful information with regard to the
Mediastinal widening, viewed on VD or DV radiographic architecture of the mass and its relationship with adjacent
views, can be secondary to diffuse mediastinal disease structures. Ultrasound-guided fine-needle aspiration or
such as mediastinitis or mediastinal fluid accumulation, or core biopsy techniques can be performed.
to focal mediastinal disease such as mediastinal neoplasia
(Figures 16.5 and 16.6). In the latter, distortion of adjacent
structures, especially the trachea, is frequently seen. Advanced imaging
Mediastinal fluid accumulation causes diffuse soft tissue CT and MRI are the most powerful imaging modalities for
opacity and may occur in conjunction with a mediastinal estimating the location, volume and invasiveness of media-
mass or secondary to inflammatory disease. Diffuse widen- stinal neoplasms (Figure 16.7). However, difficulties in distin-
ing of the mediastinum is more typical of mediastinal fluid guishing a mass from collapsed lung may be experienced
and inflammatory disease, whereas focal widening is more with both modalities. Radionuclide studies with either
consistent with a neoplasm. iodine-131 or technetium-99m have been used to identify
ectopic or metastatic thyroid tissue in the mediastinum.
Ultrasonography
Ultrasonographic examination of the normal mediastinum is Longus colli Trachea
limited by the lack of a reliable acoustic window. In the pres- muscles
ence of a pleural effusion or a cranial mediastinal mass, Great vessel
however, significant information can be acquired using Mediastinal
thoracic ultrasound examination. The transducer may be mass
positioned parasternally or alternatively at the cardiac

Lateral radiograph of a cat with a mediastinal thymoma. Computed tomographic section (bone window) through the
16.5 16.7
ing to the mass effect of the neoplasm dramatic elevation cranial thorax of a dog, cranial to the heart. A large soft tissue
of the trachea and loss of the typical cardiac silhouette are observed. A mass occupies the majority of the cranial thorax. No invasion of adjacent
soft tissue density occupies a large volume of the mid-thorax. structures such as the trachea or great vessel is observed.

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