CT after Lung Microwave Ablation: Normal Findings and Evolution Patterns of Treated Lesions

Abstract

Imaging-guided percutaneous ablative treatments, such as radiofrequency ablation (RFA), cryoablation and microwave ablation (MWA), have been developed for the treatment of unresectable primary and secondary lung tumors in patients with advanced-stage disease or comorbidities contraindicating surgery. Among these therapies, MWA has recently shown promising results in the treatment of pulmonary neoplasms. The potential advantages of MWA over RFA include faster ablation times, higher intra-tumoral temperatures, larger ablation zones and lower susceptibility to the heat sink effect, resulting in greater efficacy in proximity to vascular structures. Despite encouraging results supporting its efficacy, there is a relative paucity of data in the literature regarding the role of computer tomography (CT) to monitor MWA-treated lesions, and the CT appearance of their morphologic evolution and complications. For both interventional and non-interventional radiologists, it is crucial to be familiar with the CT features of such treated lesions in order to detect incomplete therapy or recurrent disease at early stage, as well as to recognize initial signs of complications. The aim of this pictorial essay is to describe the typical CT features during follow-up of lung lesions treated with percutaneous MWA and how to interpret and differentiate them from other radiological findings, such as recurrence and complications, that are commonly encountered in this setting.

Keywords: CT; computed tomography; lung cancer; microwave ablation; percutaneous treatments.

Figure 1

74-year-old man with a pulmonary metastasis from bladder urothelial carcinoma. (a) Cone-beam CT image of the left upper lobe metastasis (black arrow) prior MWA. (b) Cone-beam CT image obtained post-procedure shows hazy GGO of the ablation site surrounding the treated nodule (black arrow) and a small layer of lateral pneumothorax (arrowhead). (c) Axial 1-month follow-up CT image shows a large consolidation with inner cavitation (black arrow). (d,e) Axial 3-month follow-up CT image shows resolution of the cavitation and decrease in size of the consolidation (black arrow) (d) and demonstrates peripheral mild enhancement with no central contrast material uptake (white arrow) (e–g). Axial (f) and coronal (g) CT images obtained after 10 months show a residual fibrotic band (black arrow).

Figure 2

69-year-old woman with a biopsy-proved NSCLC in the right upper lobe. (a) Pre-treatment axial CT. (b) Cone-beam CT image post-MWA shows GGO (black arrow) among the ablation site. (c–e) Axial 1-month follow-up CT shows (c) a large consolidation with well-defined margins, inner hypoattenuating bubbles and a cavitation (black arrow) in communication with a peripheral bronchus (arrowhead); (d) on a different level, central necrotic material is seen within the cavitation (black arrow) (e) with no contrast enhancement (white arrow). (f,g) Axial 6-month follow-up CT images show resolution of the cavitation and decrease in size of the consolidation (black arrow) with no contrast material uptake (white arrow). (h,i) Axial 9-month follow-up CT image shows a linear fibrotic band with no contrast enhancement.

Figure 3

63-year-old woman with pulmonary metastasis from colorectal cancer (CRC) in the right upper lobe. (a) Axial CT of the metastasis (black arrow) prior to treatment. (b) Cone-beam CT image obtained post-procedure shows hazy GGO (black arrow) of the ablation site surrounding the treated nodule. (c,d) Axial 2-month follow-up CT images show a large consolidation with hypoattenuating bubbles (black arrow) and no contrast uptake (white arrow). (e,f) Axial 5-month follow-up CT images demonstrate a decrease in the size of the consolidation (black arrow) with no central contrast enhancement (white arrow). (g,h) Axial CT images obtained after 8 months show minimal further decrease in size with no signs of residual disease.

Figure 4

63-year-old-woman (same patient in Figure 3) with pulmonary metastasis from CRC in the right upper lobe. (a) Axial CT before treatment (black arrow). (b) Cone-beam CT image obtained at the end of the procedure shows GGO (black arrow) around the treated lesion. (c,d) Axial 2-month follow-up CT images show an elongated consolidation with hypoattenuating bubbles (black arrow) and no contrast uptake (white arrow). (e,f) Axial 5-month follow-up CT images demonstrate a tiny nodular uptake of contrast on the posterior margin of the consolidation (white arrow), suggestive of residual disease. (g,h) On axial CT images after 8 months the nodular enhancement persists (white arrow). (i) PET/CT image at 9 months proves residual disease on the treated lesion (white arrow) as well as simultaneous metastasis (white arrowhead) in the posterior segment.

Figure 5

77-year-old-woman with pulmonary metastasis from CRC in the right lower lobe. (a) Axial CT images prior to treatment (black arrow). (b) Prone cone-beam CT image post-MWA shows GGO of the ablation site (black arrow) and alveolar hemorrhage along the needle tract (arrowhead). (c,d) Axial 1-month follow-up CT shows a subpleural consolidation with well-defined margins, inner hypoattenuating bubbles, a central cavitation (black arrow) and no contrast enhancement (white arrow). (e,f) Axial 6-month follow-up CT images demonstrate resolution of the cavitation, decrease in size of the consolidation (black arrow) and focal uptake of contrast material (white arrow) consistent with a diagnosis of residual disease. (g) The diagnosis is confirmed by PET/CT performed at 7 months (white arrow).

Figure 6

77-year-old man with biopsy proved lung adenocarcinoma in the left upper lobe. (a) Axial CT image before treatment (black arrow). (b) Cone-beam CT image obtained at the end of the procedure shows GGO (black arrow) encircling the treated lesion and a minimal pneumothorax (arrowhead), which resolved after percutaneous drainage. (c,d) On axial CT images obtained after 1 month, there is no evidence of pneumothorax and the ablation site shows a large area of increased density, with well-defined margins and a central consolidation with inner cavitation (black arrow), without contrast enhancement (white arrow). (e,f) Three-month follow-up axial CT images show a large hydropneumothorax (black arrow) near the cavitation that is clearly in communication with a bronchus (arrowhead), consistent with a broncho-pleural fistula. (g) Axial CT image of the BPF post-pleural drainage insertion.

Figure 7

68-year-old man with a biopsy-proved squamocellular carcinoma in the left upper lobe. (a) Axial CT before treatment. (b) Cone-beam CT image at the end of MWA shows a wide GGO area (black arrow) among the ablation site. (c–e) Since persistent hydro-pneumothorax on chest X-rays is detected, CT without contrast administration is performed before the usual 1-month follow-up; axial and sagittal CT images show a large consolidation with central cavitation (black arrow); on a different level, a concomitant hydro-pneumothorax is evident (arrowhead); the diagnosis of broncho-pleural fistula is made. (f,g) Sagittal 2-month follow-up CT images show a decrease in size of the cavitated consolidation and hydropneumothorax; a communication between a bronchus and the pleural cavity is evident (black arrow); (f) the consolidation shows no contrast enhancement (white arrow). (h) Axial 4-month follow-up CT image shows a decrease in size of the consolidation with complete resolution of both cavitation and pneumothorax (black arrow).