So now we are onto evaluation of the pulmonary parenchyma. When we see something in the lungs we have to determine, "Is the
pulmonary opacity real or not?" Pulmonary opacity changes if the radiographs are obtained at the incorrect phase of the respiratory
cycle. With inspiratory radiographs, the lumbodiaphragmatic recess extends to the 12th thoracic vertebrae on the lateral view.
The accessory lung lobe is large and the cupula of the cranial lung lobe extends beyond the first rib. The retrosternal lucency
extends to the 5th sternabrae. On the VD view, the diaphragmatic cupula is caudal to T8 on inspiratory films and the costodiaphragmatic
angel to T10. Now a review of technique. For good thoracic soft tissue evaluation many shades of gray are required. High kVp
and low mAs are used to obtain these shades of gray. By comparison, with evaluation of the musculoskeletal system we want
fewer shades of gray, just mainly black and white. Low kVp and High mAs are used. Overexposed films decrease diagnosis of
pulmonary infiltrates and under-exposed films artifactually increase diagnosis of pulmonary disease. Why do we collimate?
We will now discuss the "Chabdomen" and why it doesn't work. What is a "chabdomen"? Chest and abdomen in one film. The first
problem is that thoracic films are supposed to be obtained during the inspiratory phase of the cardiac cycle, while abdominal
radiographs are supposed to be obtained during the expiratory phase of the cardiac cycle. Neither the thorax nor abdomen are
evaluated well......Next since you are taking a radiographs of the whole patient, scatter radiation is increased due to inadequate
collimation. Scatter radiation is radiation produced by interaction of x-rays with the body tissues. 50-90% of the total number
of photons emerging from the patient is scatter radiation. Only 1% of the primary x-rays actually penetrate the patient to
create the useful image, increasing scatter radiation detracts from film quality and it contributes no useful information.
FIELD SIZE IS THE MOST IMPORTANT FACTOR IN THE PRODUCTION OF SCATTER RADIATION. Radiographs taken of the whole body can miss
pulmonary metastasis due to scatter radiation degrading the overall image quality.
A few words on pulmonary metastatic neoplasia. Don't forget that without 3 radiographs when evaluating for pulmonary metastatic
neoplasia (both laterals and a DV or VD), up to 15% of pulmonary metastatic disease can be overlooked. If you are unsure if
the pulmonary nodule you see is a nipple or not, perform a "nippleogram". Place barium on the nipple in question and repeat
the VD film. Pulmonary osteomas are mineralized opacities that are less than 3mm in diameter and they can be diffuse throughout
the lungs. Do not confuse these with metastatic pulmonary neoplasia. On careful evaluation, these structures are extremely
opaque for being so small. Pulmonary metastatic neoplasia is usually round and somewhat variously sized, not all measuring
less than 3mm.
In the abdomen, this is a more random group of things to remind you of. Many of these are easily performed techniques/studies
that will aid in your diagnostic ability.
In the abdomen, a VD view is always indicated. DV views are useless and really non-diagnostic. All the organs move with gravity
and become centered on midline and you can't really evaluate the organs effectively. If you have a dyspenic or painful patient
and you need to look at the abdomen, take a lateral view only to begin with. Taking a radiograph with the dog sitting sternal
(yes with the legs underneath them) really only serves to expose your staff to radiation un-necessarily.
When you are obtaining radiographs of the caudal abdomen to evaluate dysuria/ stranguria, don't forget how long the urethra
is in a male dog. The femurs overly the urethra on a neutral lateral view. Fabella also summate with the urethra in this view,
making evaluation difficult. It takes two lateral views to fully evaluate the urethra. The "legs pulled cranially" view (ie
the butt shot) and the "legs pulled caudally" view.
You notice a mass effect in the cranial abdomen on your thoracic films. What should you do? First take abdominal radiographs
centered on the abdomen without the thorax included – is the mass still there? If so, take opposite lateral view. If it is
a "pyloric mass" or fluid filled pylorus on the right lateral view, it will become gas filled on the left laterally recumbent
view. By comparison, a mass in the tail of the spleen will be apparent in the cranioventral abdomen on both lateral views.
Abdominal compression techniques are useful to remember when evaluating for cystic calculi and other structures in the caudal
abdomen. If bowel is overlying the bladder use a wooden spoon to push the other structures out of the way so that you can
effectively evaluate without superimposition of other structures.
Now some non-pathologic findings/ structures to be remember. Ventral to the sixth lumbar vertebrae is the deep circumflex
iliac arteries. They exit the aorta perpendicularly compared to the external iliac arteries which leave at an angle from the
aorta. This causes the deep circumflex arteries to be increased in opacity on lateral views. These are located relative "high"
up in the abdomen. Do not confuse these normal anatomic structures with ureteral stones. Ureteral stones are usually located
slightly "lower" in the retroperitoneal space and are actually bone opacity. Aseptic fat necrosis used to be called a "cholesterol
cyst". This is an incidental finding in the mesentery of the abdomen (and rarely in the fat of the thorax). This appears as
a rounded, irregularly shaped less than 3cm diameter egg shell mineralized structure that is not associated with any abdominal
organ. These are hard to find with ultrasound and really you don't need to go look for them as they are non-pathologic. And
finally, adrenal mineralization in feline adrenal glands is common, often bilateral, most often appears as punctuate mineralization
cranial to the kidneys, and usually is seen on both radiographic projections.
By comparison, adrenal mineralization in dogs is pathopneumonic for adrenal neoplasia. Prostatic mineralization also is not
seen in normal patients. It should be considered adenocarcinoma until proven otherwise.