COVID-19 Pneumonia: The Great Ultrasonography Mimicker

Abstract

The pandemic spread of the new severe acute respiratory syndrome coronavirus 2 has raised the necessity to identify an appropriate imaging method for early diagnosis of coronavirus disease 2019 (COVID-19). Chest computed tomography (CT) has been regarded as the mainstay of imaging evaluation for pulmonary involvement in the early phase of the pandemic. However, due to the poor specificity of the radiological pattern and the disruption of radiology centers' functionality linked to an excessive demand for exams, the American College of Radiology has advised against CT use for screening purposes. Lung ultrasound (LUS) is a point-of-care imaging tool that is quickly available and easy to disinfect. These advantages have determined a "pandemic" increase of its use for early detection of COVID-19 pneumonia in emergency departments. However, LUS findings in COVID-19 patients are even less specific than those detectable on CT scans. The scope of this perspective article is to discuss the great number of diseases and pathologic conditions that may mimic COVID-19 pneumonia on LUS examination.

Keywords: COVID-19 pneumonia; COVID-19 pneumonia mimickers; chest computed tomography; lung ultrasound; specificity.

Figure 1

LUS artifacts. (A) Subcostal right ultrasound (US) scan with a convex probe (6 MHz). (B) Magnification on the “diaphragmatic hyperechoic line” (white arrow) showing that it is actually composed of three hyperechoic lines (1. hepatic capsule/diaphragmatic muscle interface line, 2. diaphragmatic muscle/pulmonary base interface line, 3. mirror reflection artifact) within which the real diaphragmatic muscle appears as a thin hypoechoic line (black arrow). (C) LUS scan with a convex probe (6 MHz) in a healthy individual showing the “hyperechoic pleural line” (white arrow) followed by a sporadic B-line (red arrow). (D) Longitudinal tracheal US scan with a linear probe (8 MHz) showing a “tracheal hyperechoic line” at the soft tissue/tracheal air interface (white arrow) followed by reverberation artifacts (red arrow). (E) Abdominal US scan with a convex probe (6 MHz) showing a “hyperechoic peritoneal line” (white arrow) followed by laser-like vertical and confluent ring down artifacts (red arrow). (F) Axial chest CT scan in a post-pneumonectomy patient revealing air and fluid collection in the residual space with mediastinal sliding. The intact lung is shifted toward the residual cavity. (G) US scan of the post-pneumonectomy space [corresponding to the blue box in the (F) CT scan] revealing a hyperechoic interface line (white arrow) followed by reverberation artifacts (red arrow). (H) Image of the pulmonary parenchyma of a patient diagnosed with usual interstitial pneumonia UIP during VATS. A sterile intracavitary laparoscope probe (12 MHz) with 10-mm diameter and 38-cm length (blue arrow) was introduced through one of the VATS ports in the thoracic cavity. (I) Intraoperatory LUS scan (linear probe, 12 MHz) showing an irregular increased thickness of the pleura line (white arrow) with no artifact below it. (J,K) LUS scans showing how modification of focus position (red round) can modify the number of vertical artifacts.

Figure 2

Mimickers of COVID-19 pneumonia vs. COVID-19 pneumonia. Blue boxes in CT scans indicate the corresponding US scans. (A) Axial chest HRCT of a CPE. (A') US scan with a convex probe (6 MHz) shows a blurred and thickened hyperechoic pleural line (white arrow) followed by focal and coalescent B-lines (yellow arrow). (B) Axial chest HRCT scan of ARDS. (B') US scan with a convex probe (6 MHz) shows a thickened hyperechoic pleural line (white arrow) followed by coalescent B-lines (yellow arrows). A hypoechoic consolidation (green arrow) is also viewable. (C) Axial chest HRCT scan of CMV pneumonia. (C') US scan with a convex probe (6 MHz) shows a blurred and thickened hyperechoic pleural line (white arrow) followed by coalescent B-lines (yellow arrow). (D) Axial chest HRCT scan of bacterial pneumonia. (D') US scan with a convex probe (6 MHz) shows a mixed hypo-hyperechoic lesion (green arrow) and a thickened hyperechoic pleural line (white arrow) followed by coalescent B-lines (yellow arrows). (E) Axial chest HRCT scan of an idiopathic pulmonary fibrosis. (E') US scan with a convex probe (6 MHz) shows a thickened hyperechoic pleural line (white arrow) followed by coalescent B-lines (yellow arrow). (F) Axial chest HRCT scan of OP (areas of ground glass, mild reticular pattern, and “reversed halo sign”). (F') US scan with a convex probe (6 MHz) shows a thickened hyperechoic pleural line (white arrow) followed by coalescent B-lines (yellow arrow). (G) Axial chest CT scan of a poorly differentiated lung carcinoma (histological diagnosis). (G') US scan with a convex probe (6 MHz) shows a mixed hypo-hyperechoic lesion (green arrow) interrupting the pleural line's continuity (white arrow) with an adjacent B-line (yellow arrow). (H) Axial chest HRCT scan of a lung adenocarcinoma (histological diagnosis). The neoplastic mass does not adhere to the pleural surface. (H') US scan with a convex probe (6 MHz) shows a thickened pleural line (white arrow) with coalescent B-lines below it (yellow arrow). (I) Axial chest HRCT scan showing bronchiectasis (I') US scan with a convex probe (6 MHz) shows a thickened pleural line (white arrow) followed by numerous B-lines (yellow arrows). (J) Axial chest HRCT showing pleural effusion. (J') US scan with a convex probe (6 MHz) shows a thickened pleural line (white arrow) followed by an anechoic pleural effusion (green arrow) and focal discrete B-lines (yellow arrows). (K) Axial chest HRCT showing COPD exacerbation. (K') US scan with a convex probe (6 MHz) shows a thickened pleural line (white arrow) followed by numerous B-lines (yellow arrow). (L) Axial chest HRCT showing signs of aging lung (increased broncho-arterial ratio, age-related alveolar hyperinflation, and a thoracic spine osteophyte). (L') US scan with a convex probe (6 MHz) shows a thickened pleural line (white arrow) followed by several B-lines (yellow arrow). (M) Axial chest HRCT scan of a moderate COVID-19 pneumonia. (M') US scan with a convex probe (6 MHz) shows a thickened pleural line (white arrow) followed by numerous and also coalescent B-lines (yellow arrow). (N) Axial chest HRCT scan of a severe COVID-19 pneumonia. (N') US scan with a convex probe (6 MHz) shows an unspecific mixed hypo-hyperechoic consolidation (green arrow) and a thickened hyperechoic pleural line (white arrow) followed by numerous B-lines (yellow arrow).