College Answer

There are a myriad of potential causes of a diffuse infiltrate. These include high pressure pulmonary oedema, low pressure pulmonary oedema, diffuse pneumonia, malignancy (eg. lung, haemopoetic), pulmonary haemorrhage or auto-immune/vasculitic. Most patients are able to be managed without invasive investigations.

Open lung biopsy is reserved for those situations where:

•    The cause is not apparent

•    The patient is not responding to management, or

•    There is a suspicion of another specific disease state which would require different management (eg. disseminated malignancy, alveolar haemorrhage, Bronchiolitis Obliterans Organising Pneumonia [BOOP] etc.), and

•    The diagnosis has not been able to be made on less invasive tests (eg. Broncho- Alveolar Lavage or even Video Assisted Thoracoscopic Surgery), or

•    Determination of prognosis is essential for management.

Open lung biopsy is associated with risks, especially in the critically ill patient, which include death, air-leak and even  a  sampling error (as  limited tissue removed).   These potential risks must be balanced against the information to be obtained.  The expectation is that, with further information some potentially harmful/expensive/un-necessary medications would be able to be stopped, and more specific management introduced (eg. high dose corticosteroids).

The biopsy needs to be taken from an area likely to be representative, not one with a high likelihood of non-specific fibrosis (eg. dependent segments of RML), and not too late in the disease process.(Patel 2004 Chest)

Discussion

So, you cannot arrive at a diagnosis of a diffuse interstitial infiltrate.

Lung biopsy is also asked about in Question 4 from the second paper of 2014; there the college answer is mroe comprehensive, as is the discussion.

In brief, lung biopsy is not without its risks, and is indicated only in specific situations.

Indications for lung biopsy

• diagnosis of lung disease cannot be established by less invasive means (eg. BAL, bronchoscopic biopsy, HRCT)
• the lung disease is not responding to the current management
• Management for the differentials is substantially different and a tissue diagnosis will alter the course of management
• The management suggested has significant side effects, and a biopsy may prevent such management
• Prognosis will be influenced by tissue diagnosis, and may be grounds for a palliative course of management

Complications of lung biopsy

• pneumothorax
• bronchopleural fistula
• haemothorax
• major vessel damage
• failure to establish a diagnosis due to poor sampling
• death

The biopsy must be performed in several regions of the lung, and must yield specimens which offer a representative sample, without sampling any areas of irreversible fibrosis.

It cannot be performed in patients who cannot be ventilated on one lung for prolonged periods. Risks and contraindications of of thoracotomy apply.