How to avoid common pitfalls in chest CT

2013 08 14 12 25 42 996 Eiffel Tower 200

Researchers from Paris believe it's crucial to keep aware of the common mistakes made in the interpretation of chest CT examinations encountered in daily practice. They've provided a list of nine practical tips, and received a notable award for their efforts.

The group, headed by Dr. Philippe Khafagy, from the radiology department at Montfermeil Hospital, reviewed the most frequent errors made in the interpretation of chest CT exams, focusing on the definitions of common radiological findings, anatomical points when needed, and a simple method of analysis of each sign using adequate postprocessing tools. These are their main suggestions:

  • False and benign nodules should be identified by using multiplanar reconstructions (MPR), maximal intensity projection (MIP) reconstructions, and a mediastinal window.
  • MIP and coronal reconstructions are essential to accurately characterize lobular distribution of diffuse pulmonary micronodules.
  • Pericardial recess should not be misdiagnosed with mediastinal lymph nodes: look at shape, enhancement, and contact with adjacent vessel.
  • Avoid misdiagnosis between the pulmonary cystic lesion and emphysema: look at the centrolobular artery.
  • Discriminate traction bronchiectasis from honeycombing lesions by using minimum intensity projection coronal oblique.
  • Be aware of misinterpretation of CT pulmonary angiography due to poor technique.
  • Do not overinterpret hyperattenuation of lung parenchyma as ground glass opacity (GGO) in expiratory chest CT and dependent lung areas.
  • Distinguish between alveolar consolidation and chronic atelectasis: look at the bronchi wall.
  • Do not overdiagnose pleural thickening in interscostal spaces (many anatomical pitfalls), as well as in parenchymal window; mediastinal window should be used.

When deciding if a nodule (a more or less spherical lesion measuring between 4 mm and 3 cm) requires follow-up, this is the most important question: Is it a nodule suspicious of malignancy? If so, it's important to follow the guidelines of the Fleischner Society, stated Khafagy and his colleagues, who received a certificate of merit award for their e-poster at RSNA 2015 in Chicago.

Any nodule should be analyzed in two steps using MPR, MIP, and a mediastinal window. Three frequent anomalies leading to pitfalls are flat opacities, hypertrophy of the apical caps, and bronchocele, they explained. The four main criteria for benign pulmonary nodules are fat content (mediastinal window), benign calcification content (mediastinal window), double vascular connection (MIP), and criteria of intrapulmonary lymph node (MPR).

Micronodules are spherical lesions measuring less than 4 mm in diameter. Lobular distribution, as well as lung predominance of the lesions (upper/lower or diffuse homogenous distribution), should be identified, and MIP and coronal reconstruction are essential to study the distribution of diffuse pulmonary micronodules, according to the authors.

Different methods can be used to determine lobular distribution of diffuse pulmonary micronodules. These three questions must be answered in this order: Are these micronodules of bronchiolar distribution? If not, are they of hematogenous distribution? If not, are they of perilymphatic distribution? Be aware of false tree-in-bud appearance that may be seen in perilymphatic distribution due to presence of peribronchovascular micronodules, they pointed out.

Hypertrophy of the intrathoracic lymph node is defined by the short axis (> 10 mm) for all mediastinal areas, and the most common pitfall is the physiological fluid in the pericardial recess that can give false images of intrathoracic lymph node (MPR, mediastinal window). An intrathoracic lymph node can be discriminated from the pericardial recess by shape, enhancement, and contact with adjacent vessels. Other pitfalls, which are frequent in noncontrast-enhanced CT, are the azygos vein and esophagus.

Frequent pitfalls concerning GGO and alveolar consolidation may also occur.

"Increased lung attenuation is not necessarily a GGO!" Khafagy et al wrote. "Air bronchogram with healthy bronchi is the best sign of alveolar lung filling. During expiration, there is physiological increased lung attenuation, so when GGO is suspected, check if a chest CT was done during inspiration (check the posterior border of the trachea)."

Dependent lung areas may show physiological increased lung attenuation, notably in bed-ridden and obese patients. Complementary ventral decubitus acquisition can be done to confirm the presence or absence of a GGO, they continued. Alveolar filling on emphysamatous parenchyma may mimic the appearance of honeycombing lesions, and lung consolidation on bronchiectatic bronchi should suggest chronic atelectasis (ventilated atelectasis).

Finally, pleural thickening occurs next to the ribs, not in interscostal spaces, and there are many anatomical pitfalls. Any pleural thickening seen in the parenchymal window should be evaluated in the mediastinal window: extra pleural fat hypertrophy MPR for evaluation of pleural plates versus calcified pachypleuritis. Be aware of this and check the last chest CT cuts to search for a small amount of pleural effusion, the authors advised.

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