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The collar sign
  1. K B Agrawal,
  2. R T Kamble,
  3. P Sundaram,
  4. J M Joshi
  1. Department of Respiratory Medicine, BYL Nair Ch Hospital, Mumbai Central, Maharashtra, 400 008 India
  1. Dr JM Joshi

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A previously healthy 26-year-old man presented with the chief complaint of acute onset left-sided pleuritic type of chest pain. On enquiry he gave a history of blunt trauma to the lower chest and the abdomen due to a fall 6 years earlier which had been managed conservatively. On examination, the patient was obviously distressed and had tachycardia and tachypnoea. Breath sounds were absent in the left infrascapular and infra-axillary regions. His haematological and biochemical parameters were within normal limits. Arterial blood gases revealed hypoxaemia with PaO2 66 mmHg, PaCO2 36 mmHg, pH 7.41. Chest X-ray and computed tomography (CT) scans are shown in figures1-3.

Questions

1
What is the differential diagnosis of the chest X-ray ?
2
What do the CT scans show?

Answers

QUESTION 1

The chest X-ray shows an apparent elevation of the left hemidiaphragm with a large gas collection below it. The diagnostic considerations include eventration or paralysis of the diaphragm and diaphragmatic hernia.

QUESTION 2

On a chest X-ray it may be difficult to determine whether an abdominal organ lying unusually high is located beneath an elevated hemidiaphragm (in conditions like eventration or paralysis of hemidiaphragm) or is herniating through a deficit in the diaphragm.1 In this case a diagnosis of herniation can be easily made on the basis of the CT scans, which show focal constriction of the stomach at the site of herniation (collar sign).2

Clinical course

On the basis of the clinical and radiological findings, a diagnosis of traumatic diaphragmatic hernia was made. Surgery confirmed the presence of an 8-cm tear in the posterolateral aspect of the left hemidiaphragm along with herniation of the stomach, transverse colon and spleen in the thorax. The patient made an uneventful recovery postoperatively.

Discussion

Diaphragmatic rupture occurs in approximately 5% of patients who have experienced major blunt trauma,3 and 90% of the diaphragmatic ruptures are on the left side. Left-sided hemidiaphragmatic injury predominates probably because of the protective effect of the liver on the right hemidiaphragm and/or underdiagnosis of right-sided injuries. The clinical diagnosis of laceration of the hemidiaphragm with herniated viscera is difficult, but may be suggested by bowel sounds auscultated in the lower thorax, unilateral absence of breath sounds, respiratory distress, and/or a scaphoid abdomen. Often, bedside physical findings are masked by concurrent abnormalities or these signs may be overlooked because of more apparent and life-threatening injuries in the acute post-trauma period. An early correct diagnosis is made in less than 50% of cases. Because the intrathoracic pressure is lower than the intra-abdominal pressure, there is progressive herniation of abdominal contents into the thorax. Carter et al 4 have proposed three time phases following traumatic diaphragmatic rupture. The acute phase extends from the time of injury to 14 days later. If the patient survives the initial trauma and the hernia is not manifest within the first 14 days, the second or interval phase is entered. This interval phase extends until the third stage which is the phase of obstruction or strangulation. Delayed presentation of diaphragmatic rupture with visceral herniation and strangulation is associated with higher morbidity and mortality rates than when the correct diagnosis is made and the condition managed acutely.

Chest X-ray is the principal screening method for thoracic injury after blunt trauma. Diagnostic or strongly suggestive findings on chest X-ray include the definite presence of air-filled viscera or the tip of the nasogastric tube above the diaphragm, as well as a diaphragm that is ‘very elevated’. Obscuration of a non-elevated hemidiaphragm also suggests diaphragmatic hernia. The value of chest X-rays in diagnosing right-sided traumatic diaphragmatic rupture is limited.

CT of the diaphragm has been reported to be useful in assessing for traumatic diaphragmatic rupture.5 One can usually see more of the left hemidiaphragm than the right. The posterolateral portions of both hemidiaphragms are usually best demonstrated, and thus the tears at those sites are more readily detected. The dome of the diaphragm is a difficult area to demonstrate with CT, the plane of the scan being tangential to the diaphragm at that point. The most common finding in diaphragmatic tear is a sharp discontinuity of the diaphragm. A large gap between the torn ends of the diaphragm results in the absent diaphragm sign. On the transverse CT scan, the abdominal contents lie central to the diaphragm and the thoracic contents lie peripherally. Intrathoracic herniation of peritoneal fat or organs can thus be identified by means of the abnormal position of these structures relative to the diaphragm. The structures that most commonly herniate through the defect are peritoneal fat, stomach, and colon. On transverse CT scans, to determine whether an abdominal organ lying in an unusually cephalad position, is located beneath an elevated hemidiaphragm or is herniating through a defect in the diaphragm, the presence of a focal constriction of the bowel or stomach at the site of herniation (collar sign) is very useful. The use of contrast material is essential in the demonstration of the collar sign in herniated stomach or colon when the diagnosis is made on the basis of findings in upper gastrointestinal or barium enema series.4

Learning points

  • a high index of suspicion should be maintained for the possibility of traumatic diaphragmatic hernia in all cases of blunt trauma

  • CT enables detection of the majority of such diaphragmatic tears

  • the most common findings include a localised defect of the diaphragm, the absent diaphragm sign and herniation of solid or hollow organs and omentum into the hemithorax

  • the identification of the ‘collar sign’ on CT scan helps to differentiate diaphragmatic hernia from paralysis or eventration of the diaphragm

Other imaging methods that have been reported to be of value in evaluating the diaphragm include X-rays taken after nasogastric tube placement, fluoroscopy, upper and lower gastrointestinal contrast examination, sonography, magnetic resonance imaging, contrast or air peritoneography and liver/spleen scintigraphy. The appearance of herniated liver on the nuclear liver/spleen scan is rather characteristic and its use is recommended. Newer techniques such as spiral CT scanning allow better visualisation of the dome of the diaphragm owing to multiplanar capabilities.

Final diagnosis

Left-sided traumatic diaphragmatic hernia.

References

Figure 2

Thoracic CT scan (scout scan)

View Abstract

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