Traumatic pneumatocele following a blunt thoracic injury

Clinical History

A 24-year-old motorcyclist presented with dyspnoea and left sided chest pain following a road traffic collision. Computer tomography (CT) scan revealed several traumatic lung cysts, and laceration of the spleen and left kidney, all treated conservatively.

Imaging Findings

A 24-year-old man was admitted to the hospital following a road traffic accident motorcycle versus van. On admission, he was complaining of left sided chest and abdominal pain, mild dyspnoea and haemoptysis. Clinical examination including primary and secondary trauma surveys was normal and revealed only a graze over the left iliac crest and bruising over the left side of the chest. Patient was haemodynamically stable with no hypoxaemia. Initial blood tests were unremarkable.
A plain chest radiograph showed a small left sided pleural effusion and a thin-walled cystic cavity above the left hemidiaphragm, at the level of left heart border. There was no evidence of pneumothorax (Fig. 1).
An urgent chest and abdominal CT scan was performed, which demonstrated several cystic cavities in the lower lobe of left lung (one with fluid level within it), surrounded by an area of pulmonary contusion (Fig. 2). No acute bony injury was identified adjacent to the area of pneumatoceles. In addition, a splenic and a small left renal laceration were identified.
Patient was admitted for observation and managed conservatively with analgesia and oral antibiotics (Amoxicillin). He made a good recovery and was discharged home five days post injury. A follow up chest radiograph one week after the injury demonstrated a reduction in size (from 4.2cm to 3.2cm) and thickening of the wall of the left basal pulmonary cyst.

Discussion

Traumatic pneumatocele is a rare, but well described presentation of the blunt thoracic injury [1-3]. It is defined as a thin walled, air filed cavity of the lung, which does not have epithelial lining or bronchial wall elements, and is therefore often referred to as a pseudocyst. The lesion is either the direct result of trauma itself (primary pseudocyst), or develops after resolution of pulmonary haematoma (secondary pseudocyst) [1].
The majority of traumatic pulmonary pseudocysts occur in children and young adults, mostly due to the flexibility and compliance of their thoracic wall [4-5]. A great external compressing force of trauma is transferred from the chest wall to lung parenchyma, followed by fast decompression and increase in negative intra-thoracic pressure. The rapid compression and decompression lacerates alveoli and interstitium, and subsequent retraction of surrounding lung tissue produces air and /or fluid filled cavities [4, 6].
CT scan is a very sensitive method for early detection of the pseudocysts [1, 7]. Chest X-rays alone demonstrate only about 50% of the lesions, but they are adequate for follow up [3]. On the chest radiograph, lesions may present as air-fluid spaces, with surrounding areas of consolidation due to pulmonary contusion. Computer tomography is more precise in defining the location and size of the cysts, which may appear as spherical, rounded or oval, solitary or multiple lesions. Unlike other cystic or cavitary lesions, the size and shape of the traumatic pseudocysts change relatively quickly, so series of imaging is helpful for monitoring and differentiation from other pathology [2].
Differential diagnoses include bronchogenic cyst, post-infectious pneumatocele, lung abscess, cavitating bronchial carcinoma, and visceral hernia [1-2]. These can be remembered by using a mnemonic 'CAVITY': Carcinoma, Autoimmune, Vascular, Infectious, Trauma, Young (congenital) [8]. Further on, a mnemonic 'I BAN WHIPS' may be helpful in differentiating cyst-like pulmonary lesions, including Infection, Bronchogenic cyst (Bronchiectasis, Bowel), Abscess, Neoplasm, Wegener granulomatosis, Hydatic cyst (Histiocytosis X), Infarction, Pneumatocele, Sequestration [8].
The most common clinical manifestations of the traumatic pneumatocele are cough, haemoptysis, chest pain and dyspnoea, which are not usually associated with significant hypoxaemia [1-5]. The clinical course is mostly benign, with majority of the cases resolving spontaneously within a few weeks. Treatment is typically limited to symptomatic relief, and surgical intervention is rarely required, unless complications such as haemothorax, pneumothorax, and expansion or infection of the cavitary lesion occur [2-3].

Differential Diagnosis List

Final Diagnosis

Traumatic lung pseudocysts due to blunt thoracic injury.

URL:	https://www.eurorad.org/case/8486
DOI:	10.1594/EURORAD/CASE.8486
ISSN:	1563-4086