DI mid sem notes

What is in the mediastinum

Trachea, lymph nodes and oesophagus

Normal cranial mediastinal width

<2 times the width of the vertebra

How to measure cranial mediastinal width

VD view

Measure halfway between the first ribs and the cranial border of the heart

Causes of a wide cranial mediastinum

Cranial mediastinal mass

Normal fat in the cranial mediastinum (e.g. brachiocephalic)

Ddx for masses (general)

Cyst

Haematoma

Abscess

Neoplasia

Granuloma

Brachiocephalic, deep chested and barrel chested dogs trachea

Brachiocephalic - curve more right

Deep chested - greater angle with the spine

Barrel chested - parallel to the spine

3 tracheal abnormalities

Tracheal hypoplasia

Tracheal collapse

Tracheal displacement

How to assess tracheal hypoplasia

Measured by ratio of the tracheal width to the width of the thoracic inlet

Causes of tracheal hypoplasia

Part of brachiocephalic airway syndrome

Congenital but clinical signs are more severe in puppies

How to assess tracheal collapse

Endoscopy of the trachea or fluoroscopy

Radiographs are not sensitive

Cause of tracheal collapse

Chondromalacia (softening of the tracheal rings)

Middle-aged to old small breed dogs

Redundant dorsal tracheal membrane

Can be associated with tracheal collapse

Can be seen on radiograph

If seen in a large breed dog, it is likely normal superimposition of the oesophagus

Dorsal displacement of the trachea cause

Most common: head flexed during radiography

Cranial mediastinal mass, pleural effusion, LV enlargement, LA enlargement

Ventral displacement of the trachea cause

Megaoesophagus, tracheobronchial LN enlargement

Thoracic lymph nodes

Sternal, cranial mediastinal, tracheobronchial

If you can see them, they are enlarged

Sternal lymph node location

Dogs - at the level of S2, cats - at the level of S3

Cranial mediastinal lymph node location

Multiple lymph nodes along the cranial mediastinum ventral to the trachea

Tracheobronchial lymph node location

At the carina

Displace caudal aspect of trachea ventrally

Enlarged thoracic lymph nodes Ddx

Multicentric neoplasia

Disseminated fungal infection

Metastasis from the draining area

Reactive hyperplasia

Generalised megaoesophagus causes

Transient due to GA or sedation

Idiopathic, oesophagitis, myasthenia gravis, myopathy, hypoA, hypoT

Focal megaoesophagus causes

Vascular ring anomaly

Radiographic signs of pneumomediastinum

Lateral view

Enhanced visualisation of the mediastinal structures, as the free gas provides radiographic contrast

Particularly separation of blood vessels

Pneumomediastinum causes

Blunt trauma, rupture of the trachea or oesophagus

Mediastinum communication

Cranially - communicates with the neck soft tissues (via the thoracic inlet)

Caudally - communicates with the retroperitoneum (via the aortic hiatus)

Mediastinal shift radiographic signs

Assess on the VD only

Heart ‘shifts’ to the left or the right

Causes of mediastinal shift

One side has increased volume - heart shifts away e.g. tension pneumothorax

One side has decreased volume - heart shifts towards that side e.g. lung atelectasis

Degrees of severity of pleural effusion radiographic signs

1. Pleural fissure lines

2. Retraction of the lungs from the thoracic wall

3. Lung leafing

3 causes of increased opacity in the thorax

1. Pleural effusion

2. Alveolar lung pattern

3. Mass - lung, cranial mediastinal, rib

Causes of pneumothorax

Trauma - rupture of the lung

Trauma - defect in the wall of the thorax

Spontaneous (e.g. migrating grass seed)

Radiographic signs of pneumothorax

Separation of the heart from the sternum

Retraction of the lungs from the thoracic wall

Tension pneumothorax

Check valve mechanism letting air in but not out

Increased pleural pressure

Non-tension pneumothorax

No mediastinal shift or potential shift of the heart towards the pneumothorax due to collapse of the lungs

How to assess pulmonary artery and vein

Test 1 - are they the same width

Test 2 - are they normal compared to the ribs

Lateral PA and PV width

Where the 4th rib crosses it - width of the vessel should be less than the width of the rib

VD/ DV PA and PV width

Where the 9th rib crosses them - width of the vessel should be less than the width of the rib

Caudal vena cava size

Varies with cardiac cycle so care calling it small/ dilated

Dilated if >1.5x the width of the Ao on the lateral

Ddx: PA and PV are small

Hypovascular lung pattern

Blood loss, dehydration, shock, Addisons

Ddx: PA and PV are large

Patent ductus arteriosus

Fluid overload

Left sided heart disease with secondary pulmonary hypertension

Ddx: PA is large

Heartworm disease

Pulmonary hypertension

Ddx: PV is large

Left sided heart disease

2/3’s assessment

Lateral and VD

Heart should be 2/3 of the height and width of the thorax

Intercostal width assessment

Lateral

Dog: 2.5-3.5 intercostal spaces wide, cat: 2 intercostal spaces wide

Vertebral heart score normal

Not reliable in cats

Normal dog: 8.7-10.7v

Vertebral left atrial size

Measure from the ventral aspect of the carina to the junction between the CVC and heart

Vertebral left atrial size normal

Up to 2.3 vertebrae

Heart shape assessment

Only bulges that are accurately assessed on radiographs are left atrium and main pulmonary artery

Heart disease small dog, large dog, cats

Small dog - mitral valve disease

Large dog - dilated cardiomyopathy

Cat - hypertrophic cardiomyopathy

Differentials for generalised cardiomegaly

Pericardial effusion

DCM

Peritoneal-pericardial diaphragmatic hernia

Peritoneal-pericardial diaphragmatic hernia radiographic signs

Cardiac silhouette huge

Diaphragm margin not seen

Liver small

Degenerative mitral valve disease clinical findings

Left sided apical heart murmur - severity of the murmur correlates to the severity of the disease

Causes regurgitation causing backflow of blood and LA dilation

Can cause left sided heart failure

MVD radiographic signs

Left atrial dilation

If it is severe, there will be left auricle and left ventricle dilation

Dilated cardiomyopathy clinical findings

Usually present with left sided heart failure (dyspnoea due to pulmonary oedema)

Subtle earlier signs - weakness, exercise intolerance, weight loss

DCM radiographic signs

LA dilation

Generalised cardiomegaly

Left sided heart failure radiographic signs

Pulmonary oedema

Interstitial or alveolar lung pattern in the caudal lung lobes

Pulmonary oedema in DCM is usually more patchy than MVD

Right sided heart failure radiographic signs

Pleural effusion and/ or ascites

Right sided heart enlargement radiographic signs

Radiology is very inaccurate - always take it back to the dog and go through ddx

Hypertrophic cardiomyopathy radiographic signs

In the normal cat, the heart should look like an almond on both views

In HCM, bulge in the left atrium causes a peanut and valentine shape or generalised enlargement

Radiographic signs of heart failure in cats

Cardiomegaly

Pulmonary oedema, usually patchy

Pleural effusion

Use of imaging: small dog presenting with heart murmur

Radiographs/ echocardiography to determine if LA is dilated to determine if pimobendan is indicated

Repeat in 6 months if LA is normal

Use of imaging: small dog with dyspnoea and a heart mumur

Radiographs to determine if there is heart failure (pulmonary oedema)

Use of imaging: large dog, suspect DCM

All dogs with suspected DCM should have an echocardiogram

DCM is serious and medications are expensive so a diagnosis is needed

Use of imaging: large dog, suspect LHF

Radiographs to determine if there is heart failure (pulmonary oedema)

Use of imaging: cat with cardiac abnormalities

All cats with cardiac abnormalities should have an echocardiogram

CS are often subtle so frequently present in failure without warning

Use of imaging: cat with dyspnoea

TFAST for pleural effusion

Radiography for pulmonary oedema - also can assess for cardiomegaly and pleural effusion if there is no ultrasound

Bronchial lung pattern radiographic signs

Donuts - end-on bronchi

Tram-tracks - side-on bronchi

Walls of the bronchi are not normally seen

Bronchial lung pattern dogs Ddx

Infection (bronchitis) - bacterial, lungworm, heartworm

Chronic bronchitis - old, small breed

Eosinophilic bronchopneumopathy

Normal age related if very thin and the dog is not coughing

Bronchial lung pattern cats Ddx

Feline bronchial asthma

Lungworm

Peribronchial cuffing

The bronchi are normal but appear thick due to an interstitial lung pattern increasing the opacity around the bronchus

Whenever there is an interstitial lung pattern, there will be a bronchial pattern to some degree

Alveolar (focal/ multifocal) lung pattern radiographic signs

Increased lung opacity (white lung)

Effacement - heart, diaphragm, blood vessels

Air bronchograms

Lobar sign

Alveolar lung pattern: lung opacity

Normal lung - air within the alveoli provide the black background

Seen every time and may be the only sign

Can affect part of a lobe, an entire lobe or more

Alveolar lung pattern: effacement

Effacement of the heart or diaphragm is the easiest sign to recognise so look for this

Not always seen - the lung disease has to be in contact with the heart of diaphragm

Alveolar lung pattern: air bronchogram

This is the normal bronchus seen against the abnormal white lung

Pathognomonic for an alveolar lung pattern

Not seen every time

If PA and PV can be seen either side - normal bronchus, not a bronchogram

Alveolar lung pattern: lobar sign

Abnormal white lung next to normal black lung

Therefore the border of the lung can be seen

Not seen every time

Interstitial (focal/ patchy) lung pattern radiographic signs

Increased soft tissue opacity in the lungs

The margins of organs are hazy, as the lungs are white, but they can still be seen

Interstitial vs alveolar lung pattern

Compared to an alveolar pattern, an interstitial pattern has

• No effacement (ie. the margins can be seen but are hazy)

• No air bronchogram

• No lobar border

Causes alveolar/ interstitial lung pattern

Pus

Water

Blood

Cells

Atelectasis

A/I lung pattern Ddx and distribution: pus

Pneumonia

Cranial and middle lobes (ventral parts)

A/I lung pattern Ddx and distribution: water

Oedema

Cardiogenic - often the right caudal is the first and worst affected

Non-cardiogenic - the caudal lung lobes are symmetrically affected and no signs of heart disease

A/I lung pattern Ddx and distribution: blood

Haemorrhage (coaguloapthy), contusion (trauma)

Anywhere

A/I lung pattern Ddx and distribution: cells

Neoplasia - less common (e.g. carcinoma, malignant histiocytosis)

Anywhere

Pulmonary carcinoma - can be mass, diffuse, multifocal, lobar

Histiocytic sarcoma

A/I lung pattern distribution: atelectasis

Due to recumbency - along the dependent side

Due to blockage of a bronchus (neoplasia, ET tube) - just that lung lobe

Diffuse unstructured interstitial lung pattern radiographic signs

The increased opacity is diffuse (affecting all the lung) and homogenous (not patchy)

Diffuse unstructured interstitial lung pattern Ddx

Artefact - most common

• Underinflation

• Fat dog

• Normal for age

Lymphoma

Pulmonary fibrosis

Pneumonia

Structured interstitial lung pattern

Nodules <2cm

Mass >2cm

Nodules will not be seen until they are >3mm wide - if they are less than this they are not a lung nodule

Structured interstitial pattern Ddx

Cyst

Haematoma

Abscess

Neoplasia

Granuloma

When to re-radiograph to check response to treatment

Pulmonary oedema (cardiogenic or non-cardiogenic) - 6-12 hours

Pneumonia - 3 days. Radiographs lag behind clinical improvement

Haemorrhage - pulmonary contusions usually resolve in 48-72 hours

Focal opacities that can be mistaken for nodules

End-on vessels

Pulmonary osteomas

Thoracic wall - nipples, masses

Systematic approach to thorax

1. Heart (size and shape)

2. Vessels - PA, PV, CVC, aorta

3. Lungs

4. Pleural space

5. Cranial mediastinal width

6. Trachea

7. Outside