Diaphragm Anatomy and Differential Diagnosis

Original Editor - Carin Hunter based on the course by Rina Pandya
Top Contributors - Carin Hunter, Jess Bell, Kim Jackson, Wanda van Niekerk, Lucinda hampton, Merinda Rodseth, Tarina van der Stockt and Ewa Jaraczewska

Anatomy of the Diaphragm

The diaphragm is a major muscle of respiration.

• It is a dome-shaped, "fibromuscular sheet" that separates the thorax from the abdomen.
• It forms the floor of the thorax and the roof of the abdomen.
• The left side is lower than the right - this is because the liver is situated on the right side.
• The left side may also be located partially inferiorly due to the "push" by the heart.
• The peripheral portion of the diaphragm is muscular and is composed of three distinct muscle groups:
  • The sternal group originates from the xiphoid process as two fleshy slips.
  • The costal group originates from the inner surfaces of the cartilages and adjacent parts of the six lower ribs. It "interdigitates with transversus abdominis".
  • The lumbar group originates from the two crura and the arcuate ligaments, which are in turn inserted into L1 and L2, and sometimes L3 as well.

• The central portion of the diaphragm is made up of very strong aponeurotic tendinous ligaments - these ligaments do not have any bony attachments.
  

  Figure 1. Diaphragm anatomy.

Major Openings in the Diaphragm

The diaphragm has three major openings (see Figure 1):

1. Caval hiatus: situated at the level of the T8 vertebra in the central tendon. The inferior vena cava and some right phrenic nerve branches pass through this hiatus.
2. Oesophageal hiatus: situated at the level of the T10 vertebra. The oesophagus, the right and left vagus trunks, the oesophageal branches of the left gastric vessels, and the lymph vessels pass through this hiatus.
3. Aortic hiatus: located anterior to the T12 vertebral body between the crura. The aorta, thoracic duct, and azygos vein pass through this hiatus.

Nerve Supply

Figure 2. Cervical plexus phrenic nerve.

The diaphragm is supplied by the right and left phrenic nerves, which originate from the ventral rami of C3, C4, C5 and sometimes C6 (see Figure 2). Each phrenic nerve divides into four trunks.

• Motor nerve supply:

1. The left hemidiaphragm is supplied by the left phrenic nerve
2. The right hemidiaphragm is supplied by the right phrenic nerve

• Sensory nerve supply:
  1. The phrenic nerve innervates the parietal pleura and the peritoneum, which covers the central surfaces of the diaphragm.
  2. The bottom six intercostal nerves innervate the periphery of the diaphragm
  3. The phrenic nerve is made up of large-diameter myelinated, small-diameter myelinated, and unmyelinated fibres. The large-diameter fibres fire when the diaphragm contracts, while the small-diameter fibers fire throughout respiration.
     • Activation of the phrenic nerve modulates the sympathetic motor outflow.
     • Phrenic afferents are also involved in the somatosensation of the diaphragm, and they make individuals aware of their breathing while they are awake.

Vascular Supply

Arterial supply:

• Bilateral phrenic arteries, which are the branches of the thoracic aorta
• Pericardiophrenic, musculophrenic arteries
• Tributaries from the internal mammary arteries

Venous supply:

• Inferior phrenic veins (drain into the inferior vena cava)

Fascial Attachments

Vertebrae

• Medial lumbocostal arch
  • A tendinous arch in the fascia which covers psoas major
  • Medially: attaches to the side of the L1 vertebral body
  • Laterally: attaches to the front of the L1 transverse process
• Lateral lumbocostal arch
  • A tendinous arch in the fascia which covers the upper part of quadratus lumborum
  • Medially: attaches to the front of the L1 transverse process
  • Laterally: attaches to the lower border of rib 12

Muscles

• Quadratus lumborum (QL) originates at the iliac crest and iliolumbar ligament and it inserts into the inferior border of the 12th rib, and the transverse processes of L1-L4 vertebrae. Part of the diaphragm also attaches to the superior portion of the 12th rib. The fascia is continuous between these attachments.
• Pssoas major is lateral to the lumbar vertebrae and medial to quadratus lumborum. It originates at the vertebral bodies of T12-L4, intervertebral discs between T12-L4 and transverse processes of L1-L5 vertebrae. It inserts into the lesser trochanter of femur.

When thinking about the diaphragm, we need to remember that the diaphragm and all these correlated muscles "they form a continuous chain of movements [...] the activity in one muscle group contributes to the efficiency in the other. They should all work together like a smooth machine, a well-oiled machine, whereas discrepancy, deficiency in one of these ends up compromising posture, movement, gait, cardiovascular issues, as well as digestive and oesophageal consequences." -- Rina Pandya

Aetiology of an Elevated Diaphragm

An elevated hemidiaphragm may have both direct and indirect causes. These causes can be grouped into three categories based on the location of the cause, including:

1. Above the diaphragm:
   • decreased lung volume
   • atelectasis/collapse
   • prior lobectomy or pneumonectomy
   • pulmonary hypoplasia
2. At the level of the diaphragm
   • phrenic nerve palsy
   • diaphragmatic eventration:
     • this is an abnormal placement of the diaphragm - i.e. the diaphragm is located too high in the body
     • this abnormal placement can be due to dysfunction in the nerves that supply the diaphragm or dysfunction of the diaphragm itself
     • in severe cases, diaphragmatic eventration can compress the lungs and affect respiration
   • contralateral stroke: usually middle cerebral artery (MCA) distribution
3. Below the diaphragm
   • abdominal tumour, e.g. liver metastases or primary malignancy
   • subphrenic abscess
   • distended stomach or colon, including Chilaiditi sign/syndrome
     • Chilaiditi sign is "a radiological finding that occurs when a segment of a large bowel loop or small intestine is interposed between the liver and a diaphragm."
     • Chilaiditi syndrome occurs when these changes cause gastrointestinal symptoms

Differential Diagnosis for Elevated Diaphragm

Other situations which may mimic an elevated hemidiaphragm include:

• Subpulmonic effusion
• Diaphragmatic hernia
• Diaphragmatic rupture
• Tumour of the pleura or diaphragm

Aetiology for Paralysis of the Diaphragm

Diaphragmatic paralysis occurs when the nerve supply is interrupted. This interruption might occur in the phrenic nerve, at the cervical spinal cord, or in the brainstem. It is most commonly caused by a phrenic nerve lesion:

• Mechanical trauma: such as nerve damage / ligation during surgery
• Compression: due to a chest cavity tumour
• Myopathies: including myasthenia gravis (an autoimmune disorder that affects the neuromuscular junction)
• Neuropathic: including conditions such as diabetic neuropathy, inclusion body myositis, dermatomyositis, multiple sclerosis, anterior horn cell disease, chronic demyelinating disease, and neuralgic myopathy
• Inflammation: a number of systemic diseases can cause inflammation in the phrenic nerve / diaphragm, which results in diaphragmatic palsy. Examples include:
  • viral infections (e.g. HIV, West Nile virus and poliomyelitis virus)
  • bacterial infections (e.g. Lyme disease)
  • non-infectious causes (e.g. sarcoidosis and amyloidosis)

• Idiopathic: around 20 percent of cases have no obvious cause

Differential Diagnosis for Paralysis of the Diaphragm

• Alveolar hypoventilation
• Anterior horn cell or neuromuscular junction disease
• Cerebral haemorrhage
• Cervical fracture
• Decreased pulmonary compliance
• Guillain-Barre syndrome
• Myasthenia gravis
• Peripheral neuropathies
• Pleural adhesions

Symptoms of Diaphragmatic Weakness

1. Unilateral weakness: Often asymptomatic and detected incidentally. Patients show limitations in exercise capacity and lower oxygen saturation levels:
   • One-third of patients complain of exertional breathlessness
   • Individuals who have "coexisting debilitating cardiopulmonary conditions" might have dyspnoea at rest
2. Bilateral weakness: patients report varying levels of dyspnoea (i.e. from breathlessness with mild exertion to dyspnoea at rest. When diaphragm function is further compromised, patients tend to have orthopnoea (i.e. breathlessness when lying supine.

Progressive hypoventilation can lead to hypercapnia and right heart failure. Hypoxaemia and hypercapnia will be worse when a patient is sleeping.

Paradoxical Breathing

Figure 3. Paradoxical breathing.

Paralysis of the diaphragm results in a "paradoxical movement" (see Figure 3). Typically, when we inhale, the diaphragm lowers and flattens, which causes bulging / blowing / elevation of the stomach. During expiration, the diaphragm relaxes, so it can return to its original position (i.e. dome-like shape), and there is a passive drop of the belly.

In paradoxical breathing, this process happens in the reverse order. The diaphragm moves up during inspiration and down during expiration.

• Unilateral diaphragmatic paralysis is frequently asymptomatic and is often found incidentally on x-ray.
• Bilateral paralysis can result in poor exercise tolerance, orthopnoea and fatigue. There will also be a restrictive deficit on lung function tests.

The following optional video provides a demonstration of paradoxical breathing.