3 Imaging anatomy (copy)

What is serosal detail?

Serosal detail refers to how well the organs are seen in the peritoneum (ie. how wel you can see the outside margin of the organs)

What does decreased serosal detail indicate?

Decreased serosal detail indicates abdominal fluid

Can also be caused by: a mass, skinny body condition, a young animal, technique issues (DDx = MFSTY)

What is the peritoneum?

The peritoneum is the serous membrane lining the abdominal cavity, containing most abdominal organs

What is the retroperitoneum?

The retroperitoneum is the space in the dorsal abdomen outside the peritoneum, where the kidneys are located

Fat opacity

How can you determine if fluid is in the peritoneum or retroperitoneum?

If in the peritoneum, all abdominal organs are obscured

If in the retroperitoneum: spinal muscles are poorly defined, kidneys are poorly visualised

How is the gastric axis determined?

The gastric axis is determined by the line between the fundus (cranial dorsal abdomen next to the diaphragm) and pylorus (needs to be seen), assessed in the lateral view

What is a normal gastric axis?

The axis should be between parallel to the ribs and perpendicular to the spine

What indicates a change in the gastric axis?

A change in the gastric axis indicates a change in the location of the pylorus (fundus is fixed at the cardia)

How can liver size be assessed using the gastric axis?

If the gastric axis is not in a normal position, it may indicate liver enlargement

In lateral view assess the caudoventral margin (rounded margin indicates hepatomegaly)

In VD view assess the shape and size - stomach has a U-shape if the liver is large

When can you see the head of the spleen?

Should be seen on VD (not lateral) in every cat and dog

When can you see the tail of the spleen?

Normal to be seen or not seen on lateral view in dogs

Should NOT be seen in cats - indicates splenomegaly

How can you assess kidney size?

Comparison to L2 only on VD view

Assess whether they are the same size as each other and the normal size compared to L2

What is the normal size range for a cat's kidney compared to L2?

1.9 - 2.6 times the length of L2 vertebra

What is the normal size range for a dog's kidney compared to L2?

2.5 - 3.5 times the length of L2 vertebra

What is the expected appearance of the kidneys in dogs?

Lateral - right kidney more cranial

VD - right slightly more cranial, but only the caudal pole is seen (cranial pole is effacing with the liver

What is the expected appearance of the kidneys in cats?

More easily seen - usually both are seen on both views

More parallel

More mobile

How long can ingesta remain in the stomach?

Ingesta can remain in the stomach for 3 days (longer in hospital compared to at home)

Dog stomach will usually be mostly empty after 24h, cats usually after 8 hours

Liquid remains in the stomach for a maximum of 2 hours

How can you determine the location of the fundus and pylorus?

Best seen on right lateral

Fundus is dorsal and left and pylorus is ventral and right

What is the normal size of the stomach?

In a fasting dog, the fundus should be <3 intercostal spaces wide

In a fasting cat, the stomach should be empty

Why can't you assess the width of the wall of the small intestine?

The wall of the small intestine and the fluid within it are the same opacity (soft tissue opacity). As they are in contact with each other, they will efface - this artefactually makes the wall look thick

What is the normal width of the small intestine in dogs?

Less than 1.6 times the L5 vertebra at the narrowest part

What is the normal width of the small intestine in cats?

Less than 2 times the L5 vertebra height of the endplate

What is the significance of the duodenum's location on a radiograph?

The duodenum is expected to be located in the right cranial abdomen, but is superimposed on the colon so is difficult to see in dogs and cats

What is the expected location of the caecum on a radiograph?

Only seen in the dog at approximately the level of L3

Describe the normal location of the colon

Lateral - divides the abdomen in half dorsoventrally (ascending, transverse and descending are superimposed)

VD - question mark shaped

What organs shouldn't be seen on the lateral projection?

Sublumbar lymph nodes

Uterus / Uterine stump

Prostate (if neutered)

List the 4 locations for abdominal masses

Cranial

Retroperitoneal (can't differentiate from mid on VD)

Mid

Caudal

Cranial abdominal masses

Displace stomach caudally

Almost always liver

Retroperitoneal masses

Assess on lateral - stays dorsal

Can be a mass (kidney or adrenal) or fluid

Mid abomdinal masses

Assess on lateral

Usually spleen

Caudal abdominal masses

Displace the small intestine cranially or colon dorsal/ ventrally

Distended bladder, lymph nodes, prostate, pyometra

What is the main difference between the cat and dogs stomach on VD?

Cat - J shaped and the pylorus is midline

Dogs - pylorus is on the right

List three ways you can assess heart size

2/3 assessment on lateral and VD

Intercostal width on lateral

VHS/ VLAS on lateral

What is a normal 2/3 assessment?

Heart should be 2/3 the height on the lateral view and 2/3 the width on the VD view of the thorax

Height = ventral aspect of carina to apex of heart

What is the normal size of the heart in intercostal spaces?

Dog - 2.5 to 3.5 intercostal spaces wide

Cat - 2 intercostal spaces wide

What is the normal vertebral heart score range?

Objective - height and width (on lateral) against vertebra (cranial aspect of T4)

Dogs - 8.7 to 10.7 vertebrae

Not reliable in cats

How is the left atrial size measured?

From the ventral aspect of the carina to the junction between the CVC and heart

Normal is up to 2.3 vertebra

How can you assess chamber enlargement (bulges in the heart)?

Don't look at left ventricle or right side of the heart

Can only accurately assess the left atrium and the main pulmonary artery

When can you see the pulmonary artery/ pulmonary vein?

Only assess the cranial lobe of pulmonary artery and vein on the lateral projection

Only assess the caudal lobe of pulmonary artery and vein on the VD projection

How can you assess the pulmonary artery and pulmonary vein?

Are they the same width?

Lateral - width of the vessels should be less than the width of the dorsal 4th rib where they cross

VD - width of the vessels should be less than the width of the 9th rib where they cross

How can you tell if a radiograph is a right or left lateral?

Using the crura (musculotendinous bands anchoring the diaphragm to the lumbar vertebrae) of the diaphragm

Left lateral = crura form a Y shape

Right lateral = crura are parallel

What is the normal appearance of the caudal vena cava on radiographs?

It runs into the right crus

Dilated if >1.5x the width of the Ao

How can you determine which lung lobes a mass is located in?

If seen more clearly on left lateral, its in the right lung (as right lung floats to the top)

Determine lobe by location

What are the two types of pathology that affect the pleural space?

Pleural effusion (fluid)

Pneumothorax (gas)

What is the primary function of the visceral pleura?

To line the lungs

What is the primary function of the parietal pleura?

To line the thoracic wall

What are pleural fissure lines indicative of?

Pleural effusion (fluid in the pleural space)

Don't normally see these as the lung lobes are the same opacity as each other

What structures are included in the cranial mediastinum?

Extends from the first ribs to the cranial aspect of the ribs

Trachea, oesophagus, blood vessels, lymph nodes

How is cranial mediastinal width measured?

On the VD view, halfway between the first ribs and the cranial border of the heart

What is the normal cranial mediastinal width?

Less than 2 times the width of the vertebra

Wider in brachycephalic and obese dogs

Where are the sternal lymph nodes located?

At the level of S2 in dogs and S3 in cats

Where are the cranial mediastinal lymph nodes located?

Multiple lymph nodes along the cranial mediastinum ventral to the trachea

Where are the tracheobronchial lymph nodes located?

Lymph nodes at the carina

Displace the caudal aspect of the trachea ventrally

What imaging modalities are commonly used for limb assessment?

General practice - radiographs

Referral practice - radiographs, CT, MRI

What are sesamoid bones?

Small bones embedded in muscles or tendons to relieve tension

What is the diaphysis?

The shaft of the bone

What is the metaphysis?

Between the physes (growth plate) and the diaphysis

What is the cortex?

The dense bone around the outside

Has a fibrous cover called the perioosteum

When do directional terms change from cranial and caudal to dorsal and palmar/ plantar?

Proximal to the carpus/ tarsus, head side is cranial and tail side is caudal

Distal to the carpus/ tarsus, head side is dorsal and tail side is palmar/ plantar

How can you assess whether the soft tissue structures are normal?

To determine if the soft tissues are normal in the limb that is lame, the other limb (the non-lame limb) is always radiographed for comparison

increased = swelling, decreased = muscle wasting

What is the subchondral bone?

Bone that is within the joint, lined by articular cartilage

What does the joint space on a radiograph represent?

The area between subchondral bone and articular cartilage (SF opacity so can't be seen), filled with joint fluid and soft tissue (synovium, menisci, intra-articular ligaments)

What is the intervertebral foramen?

Where the nerves come out of the spine

What is the facet joint?

Synovial joint where the vertebrae articulate

Cervical - are located laterally so they superimpose over the spinal canal on the lateral view

Thoracic and lumbar - are located dorsal to the vertebral canal on the lateral view and are easier to assess

What is the vertebral formula?

Cd20-24

C7 - T13 - L7 - S3

What is the significance of the T10/11 vertebrae?

It is anticlinal, changing the direction of spinous processes

What is the significance of the T13 vertebrae?

Where the last rib is attached to - ribs articulate at the cranial aspect of the vertebrae

What is the significance of the C1 vertebrae?

Atlas - has wings (large transverse processes)

What is the significance of the C2 vertebrae?

Axis - has a long thin spinous process (dorsally)

What is the significance of the L3/L4 vertebrae?

The ventral margin is poorly defined as the diaphragm attaches here

What is the role of the intervertebral discs?

They provide cushioning between vertebrae and allow movement

What is the normal appearance of the intervertebral disc spaces?

Adjacent disk spaces in the same region are usually about the same width

Disk space of C7-T1 and T10-11 is normally narrower than adjacent disk spaces

What should be assessed in a systematic approach to the spine?

Cranial to caudal

Vertebral bodies, end plates, intervertebral disk spaces, vertebral canal, intervertebral foramina, facet joints