Raised Hemidiaphragm On Chest X-ray

An abnormally elevated hemidiaphragm on chest radiography is defined as a right hemidiaphragm sitting more than 2cm higher than the left, or a left hemidiaphragm sitting at the same level or higher than the right 1

In a normal chest radiograph, the dome of the right hemidiaphragm overlaps anteriorly with the fifth or sixth rib and posteriorly with the tenth rib. The dome of the left hemidiaphragm is usually one interspace lower than the right. In up to 10% of healthy subjects, however, both diaphragmatic domes are at the same height 2, 3

There are many causes for unilateral hemidiaphragm elevation on chest radiography. This includes pathology related directly to the diaphragm or its innervation causing weakness or paralysis (diaphragm dysfunction), or pathological processes in the thoracic or abdominal cavities that indirectly cause or mimic diaphragm elevation. When a raised hemidiaphragm is seen on chest radiography it is important to look for these causes. In many cases, these may not be visible and further investigations are required 3-6

Recent guidelines from the Canadian Association of Radiologists recommend fluoroscopy or ultrasound as the initial imaging modalities in patients with suspected phrenic nerve palsy 7

Diaphragm dysfunction includes weakness (partial loss of muscle strength) or paralysis (total absence of muscle strength) 6,8

There are a number of causes of diaphragm dysfunction. It can occur due to any interruption of the neurological pathway from the brain, spinal cord, and phrenic nerve, to problems at the neuromuscular junction or with the muscle of the diaphragm itself 6, 8

Causes are generally classified as: 1, 9

• Compressive or infiltrative processes (e.g. mediastinal or pulmonary malignancy, pathological lymph nodes, cervical arthrosis and spondylosis)

• Traumatic lesions (e.g. cardiothoracic or neck surgery). Phrenic nerve injury is often seen following coronary artery bypass surgery with the incidence of post-operative diaphragm paralysis reported to be between 1-60% 1

• Inflammatory disease (e.g. shingles, mononeuritis, chronic demyelinating polyneuropathy). Recently there have been reports of COVID-19 infection being associated with unilateral diaphragmatic paresis. 10

• Central neurological disease (e.g. stroke, multiple sclerosis)

• Idiopathic

Recent guidelines from the Canadian Association of Radiologists recommend fluoroscopy or ultrasound as the initial imaging modalities in patients with suspected phrenic nerve palsy 7

Common alternative causes of unilateral hemidiaphragm elevation include: 1, 11, 12

There are a number of mimics including: 11

Non-invasive, portable, quick, simple and well-tolerated which allows quantitative and qualitative assessment of diaphragmatic movement 1, 5, 6, 13

Has been suggested as the technique of choice for assessing diaphragmatic movement and has been shown to be more sensitive than fluoroscopy for evaluation of diaphragm weakness 1, 6, 13, 14

Considered the preferred examination in children and young adults owing to the absence of ionising radiation 8, 15

Is of particular value in the intensive care setting for excluding diaphragm paralysis after cardiothoracic surgery unlike fluoroscopy which requires the patient be transported often with haemodynamic monitoring and infusion lines in place 15-18

The main variables that can be assessed include static measurement of diaphragm thickness and dynamic evaluation of inspiratory diaphragm thickening fraction and excursion. Similar to fluoroscopy, when visualised on ultrasound, hemidiaphragm mobility can appear absent or paradoxical during breathing at rest, and a paradoxical movement is seen on sniffing when diaphragm dysfunction is present 1, 19, 20

With appropriate methodology it has good intra- and inter-observer reliability and reproducibility 6, 13

Sensitivity and specificity for detection of diaphragm dysfunction in neuromuscular disease has been reported to be 93% and 100% respectively 6

The thickness of the diaphragm can be determined in the majority of patients (85%) to assess for eventration 6

Also allows visualisation of structures above and below the diaphragm to look for other causes of an elevated hemidiaphragm (e.g. pleural fluid, subphrenic abscess, hepatic abscess) 5, 17

Some authors have found M-mode ultrasound to be useful during quiet breathing, voluntary sniffing and deep breathing to detect diaphragmatic dysfunction in patients at risk 19

Limited in that it has a small field of view, and in particular the left hemidiaphragm may be difficult to visualise in the presence of obesity or gaseous distension. For these reasons, some authors suggest that ultrasound should be used when fluoroscopy cannot be performed or cannot be interpreted (e.g. when there is diaphragm obscuration from adjacent pleural fluid or parenchymal consolidation) 3

Allows visualisation of the diaphragm continuously throughout the normal respiratory cycle and during certain inspiratory manoeuvres (e.g. sniff test of Hitzenburger) 6, 21

During a sniff manoeuvre, a paradoxical upward motion of the abnormal hemidiaphragm may be observed which indicates unilateral paralysis. The sniff test has been found to be positive in over 90% of patients with unilateral diaphragm weakness 1, 2, 5, 21

Previously the gold standard for diagnosis of diaphragm paralysis 6, 21

Some authors recommend fluoroscopy be performed in a recumbent (decubitus) position as some patients compensate for a lack of diaphragmatic movement in an upright position by adopting unusual respiratory patterns, leading to errors in interpretation 6, 22

In bilateral diaphragm weakness, fluoroscopy findings can be misinterpreted and often results in false negatives for true diaphragm paralysis 1, 2, 6, 21

There are several other drawbacks including: it is rarely compared to a reference technique making estimates of its sensitivity and specificity imprecise, it is dependent on patient effort and cooperation (patient needs to breathe spontaneously and be disconnected from any source of positive pressure ventilation), and it only provides a semi-quantitative evaluation of diaphragm function, making repetitive prospective measurements difficult to compare 1, 15

Dynamic chest radiography (DCR) is a novel real-time digital fluoroscopic imaging system that has shown promise in the investigation of diaphragmatic dysfunction 23

Not usually performed routinely to evaluate diaphragmatic function 2

May be helpful to look for abdominal pathology (e.g. subdiaphragmatic abscess, ascites, organomegaly) contributing to diaphragm elevation seen on a plain chest radiograph 2, 24

May help in further evaluation of lung parenchyma and pleura (e.g. suspected obstructive disease, subpulmonic effusion, pleural thickening) 2, 24

Imaging modality of choice to assess for a mediastinal mass which can cause compression/infiltration of the phrenic nerve and result in diaphragm dysfunction 25

A recent limited study of CT in patients with US-proven diaphragm dysfunction revealed thinner diaphragm pillars as measured on CT. Additionally, a notable increase in the difference in diaphragmatic height demonstrated a strong potential to identify diaphragmatic dysfunction.26