The target sign in COVID-19 pneumonia

Alexandre Marchini Silva, MD¹; Pamela Bertolazzi, BS²

¹ Radiology Department, Fleury S.A., Paraíso, Sao Paulo, SP, Brazil

² Siemens Healthineers, LAM

2022-02-11

Axial and coronal images show the target sign and its variant. Multiple GGOs and sparse foci of consolidation are shown bilaterally with a predominant peripheral distribution.

Download your PDF here. (pdf) 0.7 MB

History

A 15-year-old male patient, suffering from mild fatigue and a non-productive cough, had a positive RT-PCR test and was diagnosed with COVID-19. His treatment did not require hospitalization and an oxygen saturation test was normal. Three weeks later, the patient returned for a follow-up CT chest examination.

Diagnosis

CT images showed bilateral multiple ground-glass opacities (GGO) and sparse foci of consolidation in all lobes, affecting 25–50% of the lung parenchyma and showing a predominant peripheral distribution. The presence of a nodular opacity in the center of the ring-like opacity, resembling a target sign, was observed bilaterally in the axial, coronal and sagittal planes. This was consistent with what had been described in previously published cases, suggestive of COVID-19 pneumonia. The patient was referred to a pulmonologist for further treatment.

Images in axial, coronal and sagittal planes show the target sign and its variant. Multiple GGOs and sparse foci of consolidation are shown bilaterally with a predominant peripheral distribution. — Courtesy of Radiology Department, Fleury S.A., Paraíso, Sao Paulo, SP, Brazil

Fig. 1: Images in axial (Figs. 1a–1c), coronal (Figs. 1d–1e) and sagittal (Figs. 1f–1g) planes show the target sign (arrows) and its variant (dotted arrow). Multiple GGOs and sparse foci of consolidation are shown bilaterally with a predominant peripheral distribution.

Comments

The target sign, characterized on the chest CT images, corresponds to a central nodular opacity surrounded by a dense peripheral rim or a ring-like opacity. It was first described by Müller et al. in a COVID-19 pneumonia case. [1]

A variant of the target sign, characterized by multiple concentric perivascular ring-like opacities, has also been demonstrated in other cases. [2] In this case, both the target sign and its variant are observed.

Pulmonary vascular alterations have been associated with COVID-19, indicating that the central nodular opacity may reflect perivascular angiocentric inflammation or focal enlargement of the pulmonary artery. [4, 5] The ring-like opacities can be correlated with the underlying pathophysiologic mechanisms of the disease process as it organizes itself, indicating that the organizing pneumonia is one of the mechanisms of lung injury. [2] Marchiori et al. contributed to the discussion, showing that the target sign is not specific to COVID-19, and can be seen in conditions other than organizing pneumonia, including osteosarcoma metastasis. [3]

A CT chest examination plays an important role in the clinical management and assessment of the complications of COVID-19 pneumonia, as well as to exclude alternative diagnoses. Although the target sign is nonspecific, and the confirmation of its potential usefulness still requires further evaluation, it may help in suggesting the diagnosis of COVID-19 pneumonia within proper clinical settings. [1]

Examination Tools

Scanner	SOMATOM Definition Edge
Scan area	Thorax
Scan mode	Spiral
Scan length	293.6 mm
Scan direction	Caudo-cranial
Scan time	2.6 s
Tube voltage	100 kV
Effective mAs	72 mAs
Dose modulation	CARE Dose4D
CTDI_vol	2.9 mGy
DLP	115.3 mGy*cm
Rotation time	0.33 s
Pitch	1.2
Slice collimation	128 x 0.6 mm
Slice width	1.0 mm
Reconstruction increment	1.0 mm
Reconstruction kernel	B45f

Avez-vous jugé cette information utile?

The outcomes by Siemens Healthineers’ customers described herein are based on results that were achieved in the customer’s unique setting. Because there is no “typical” hospital and many variables exist (e.g., hospital size, case mix, level of IT and/or automation adoption) there can be no guarantee that other customers will achieve the same results.

[1] Müller CIS, Müller NL. Chest CT target sign in a couple with COVID-19 pneumonia. Radiol Bras. 2020 Jul/Ago; 53(4):252–254.

[2] Gomes de Farias LP, Caixeta Souza FH, da Silva Teles GB. The Target Sign and Its Variant in COVID-19 Pneumonia. Radiology: Cardiothoracic Imaging 2020; 2(4):e200435.

[3] Marchiori E, Silva J.A.M, Amorim, V.B., Zanetti, G. Is the CT target sign specific to COVID-19 pneumonia? J Bras Pneumol. 2020; 46(6):e20200541.

[4] Lang M, Som A, Carey D, et al. Pulmonary vascular manifestations of COVID-19 pneumonia. Radiol Cardiothorac Imaging 2020; 2(3):e200277.

[5] Ackermann M, Verleden SE, Kuehnel M, et al. Pulmonary Vascular Endothelialitis, Thrombosis, and Angiogenesis in Covid-19. N Engl J Med 2020; 383(2):120–128.