CT scan of the chest

CT scan of the chest is one of the major applications of CT scan. There are several indications for CT scan of the chest. Most of the mediastinal and lung paranchymal diseases are required CT scan to come in to a diagnosis and to define the extensions of the diseases. Lung paranchymal and mediastinal tumors or cancers are the conditions detected by CT scan of the chest.

CT is much more sensitive than plain radiographs for the detection of mediastinal and parenchymal lung disease. CT scan of the chest is used to stage or to grade lung cancer and identify nodal disease (metastais to lymph nodes). However, CT and MRI use size as the only criteria for malignant involvement of lymph nodes;

• nodes <1 cm are considered normal (even if there are metastasis)
  
• nodes >1 cm are considered malignant (even if they are reactive).

Therefore, patients will be over- and understaged and a metabolic method such as positron emission tomography (PET) using fluorine- labelled fluorodeoxyglucose 18F FDG will aid more accurate staging. This is one of the drawbacks of CT scan of the chest. The development of hybrid machines combining PET and CT has improved the anatomic localization of PET. MRI is as good as CT for the mediastinal staging of lung cancer, but is less effective for parenchymal lung disease and is usually reserved for staging Pancoast tumours and assessing invasion of the vertebral or chest wall in lung cancer. The assessment of parenchymal lung disease is best performed using high-resolution CT for the diagnosis of fungal disease in the immunosuppressed and in identifying lung metastases. CT is used to rapidly assess the thoracic aorta in suspected dissection and it has modified the investigation and diagnosis of pulmonary thromboembolic disease. Ventilation/perfusion lung scans are very accurate if the chest radiograph is normal, but their diagnostic efficacy falls if it is abnormal. In these instances, a CT pulmonary angiogram can be performed with identification of emboli in the main and segmental arteries, but limited visualization of subsegmental emboli. The improved spatial and temporal resolution of the newer scanners will allow coronary angiography to be undertaken, though conventional angiography is required for the very distal arterial branches.