Qureshi and colleagues achieved impressive results using thoracic ultrasound (TUS) to predict malignant pleural effusion in their recent study.1 TUS in their hands compared reasonably well with pleural CT.

However, we suggest that pleural CT still remains the gold standard and cannot be replaced by TUS except in situations where access to pleural CT is difficult. First, even in their expert hands, six out of the seven false-negative TUS examinations were resolved by pleural CT. The priority in the real world is to reduce the time to pleural CT which is the definitive investigation. In our experience, TUS is complementary to pleural CT but more helpful and informative after the CT to aid pleural intervention due to information from two different imaging modalities.

Secondly, this study was performed in a tertiary pleural centre by an extremely experienced internationally renowned thoracic radiologist and another thoracic radiologist with a special interest in pleural ultrasound in a cohort with a high proportion of mesothelioma. In addition, the proportion of pleural tuberculosis (TB) cases was low, but this remains an important differential in TB-prevalent populations. We suggest the results are not generalisable to TUS performed by non-radiologists with Royal College of Radiologists sublevel 3 training.2 Although pleural thickening is commonly measured, the exact measurement of diaphragm thickness, resolution of all diaphragmatic layers and evaluation of diaphragmatic/pleural nodules and liver metastases are not performed routinely by sublevel 3 operators. These aspects of TUS are more complex than an “x marks the spot” to aid thoracocentesis that is commonly used by chest physicians.

Finally, pleural CT offers additional benefits. It can detect primary lung cancer, unsuspected primary non-lung cancer and metastatic disease (bone, liver) at the same time. In addition, it can detect TB pulmonary disease such as cavitation and extrapulmonary disease, as well as evaluating asbestos-related disease by examining the mediastinal pleura and looking for contralateral changes. Pleural CT is unlikely to be substituted when radical treatment of mesothelioma is contemplated. Although liver metastases are readily detected at TUS, most of the above changes are not reliably detected.

In conclusion, we suggest the real world priority is to perform pleural CT promptly. TUS is complementary but not a substitute, and more helpful after pleural CT. A simple “x marks the spot” will normally suffice for most interventions, although knowledge about septation may assist with planning thoracoscopy.