Traumatic lung hernia: multidetector CT findings and relevance

Clinical History

A lady presenting to the emergency department for persistent pain the day after a domestic fall with left-sided blunt chest trauma. She was found slightly dyspnoeic with signs of blunt impact over her left lateral chest at physical examination, with stable cardiorespiratory parameters and arterial blood gas values within normal limits.

Imaging Findings

The patient had a history of allergy to iodinated contrast medium and normal findings on previous chest radiographs (not shown).
Plain radiographs (Fig. 1) revealed post-traumatic left-sided subcutaneous emphysema from the supraclavicular region and posterior paravertebral muscles to the iliac crest, fractured 8th rib, and a sizeable basal opacity with air-fluid level consistent with pulmonary laceration. Ultrasound assessment of the spleen (Fig. 2) was hampered by “hazy” posterior shadowing from extrathoracic emphysema. Crepitance was palpable along the left hemithorax.
Urgent unenhanced multidetector CT (Fig. 3) confirmed emphysema, dislocated rib fracture and pulmonary laceration with dependent blood. Additionally, CT showed minimal ipsilateral pneumothorax, normal-sized homogeneous spleen, absent haemoperitoneum. Part of the lower left pulmonary lobe herniated outside the thoracic cage through the injured intercostal space, as further depicted by minimum-intensity projection and volume-rendering views (Fig. 3 i, j).
The patient was sent to thoracic surgery to undergo prompt hernia repair.

Discussion

A traumatic lung hernia (TLH) represents an uncommon consequence of blunt thoracic trauma with approximately 300 reported cases in the literature, the majority occurring after motor vehicle accidents. Represented by the protrusion of pulmonary tissue covered by pleural membranes through a traumatic defect in the thoracic wall, TLH is more likely when the injury mechanism involves a sudden marked increase of intrathoracic pressure such as in seatbelt-restrained individuals. Herniation most commonly occurs at the antero-lateral chest wall, which has limited muscular support compared to the posterior chest in the site of rib fractures and torn intercostal muscles. Alternatively, TLHs may sometimes develop in the site of costochondral junction fractures. The unspecific symptoms of TLH include pain, coughing, haemoptysis, shortness of breath. Sometimes, physical examination may detect a fluctuating mass with overlying crepitus. Sometimes, the diagnosis is delayed weeks or months after the trauma [1-4].
The antero-posterior chest radiograph traditionally represents the initial technique used to investigate blunt thoracic trauma. In TLH, plain X-rays may reveal a contained radiolucency in the chest wall, which may be apparent and expand paradoxically in forced expiratory views obtained to exclude pneumothorax, or during Valsalva’s manoeuvre. However, TLHs may be radiographically obscured by emphysema or haematoma, and is easily missed when the X-ray beam is not tangential to the hernia [1, 2, 5, 6].
Multidetector computed tomography (CT) is the preferred and most accurate modality to detect and characterize traumatic chest injuries, and CT findings have been consistently found to impact the patients’ management. As this case exemplifies, CT including multiplanar, minimum intensity projection (minIP) and volumetric reformatted images clearly depicts the traumatic orifice in the thoracic bony and muscular cage and the herniated lung portion: the improved anatomical visualization provided by CT is of value to the thoracic surgeon for the treatment planning [1, 5-8].
Spontaneous resolution of a TLH is uncommon. Since TLHs may grow and eventually undergo incarceration or strangulation under positive-pressure ventilation, the diagnosis should be made before patients are intubated and undergo general anaesthesia for other reasons such as splenic injury. Some asymptomatic patients may be treated conservatively. Conversely, immediate open or thoracoscopic surgical exploration is required for most intercostal hernias, to assess viability of the herniated lung portion, reduce the TLH and repair the defect with a muscle flap or synthetic prosthetic graft [9, 10].

Differential Diagnosis List

Final Diagnosis

Traumatic intercostal lung hernia

URL:	https://www.eurorad.org/case/12819
DOI:	10.1594/EURORAD/CASE.12819
ISSN:	1563-4086