A 38-year-old man was referred to our clinic 6 months after initial diagnosis of poorly differentiated thyroid carcinoma (TNM: pT3a pN1b pM1). Prior to resection of radioiodine-negative pulmonary metastases, perfusion scintigraphy was requested for preoperative risk evaluation, as sequential bilateral metastasectomy was planned. In addition, the patient showed a reduced lung reserve in pulmonary function testing (maximum vital capacity 3.9 L, 80% of the nominal value; forced vital capacity 3.5 L, 69% of the nominal value; forced expiratory volume in 1 s 2.9 L, 71% of the nominal value). Thoracic SPECT imaging after application of 99mTc-macro-aggregated albumin (MAA) demonstrated multiple bilateral pulmonary (multi-)segmental (right lower lobe, middle lobe, left upper lobe) and subsegmental (e.g., right upper lobe) perfusion defects (Fig. 1A–C). Subsequently performed ventilation SPECT using 99mTc-Technegas did not show any impairment (Fig. 1D–F). The V/P mismatches were highly suspicious of multifocal PE. However, the patient did not report symptoms of PE. Both blood panel and spirometry did not reveal any pathological findings; oxygen saturation was 98.5%. The clinical pretest probability for PE was low with a Wells score of 1 and a revised Geneva score of 2. In combination with the clinical findings, PE was deemed unlikely; therefore, no anticoagulation treatment was initiated. The planned resection was extended to left pulmonary and left hilar metastasectomy: 8 pulmonary wedges containing metastases (S3, S4, upper lobe/lingula, S10, lower lobe/diaphragm surface) and an aortopulmonary window lymph node metastasis were resected. Another hilar metastasis was not removed because of its close proximity to the upper lobe artery. As subsequent right-sided metastasectomy was considered, a follow-up perfusion SPECT was performed 2 weeks after left-sided metastasectomy. Left-sided pulmonary perfusion was normalised apart from one newly occurring subsegmental defect in left inferior lobe segment S10 (Fig. 1H) interpreted as post-surgical (compare Fig. 1B and H), while perfusion defects on the right side that had not underwent surgery remained unaltered (Fig. 1G–I). Within 1 week after the second perfusion SPECT, 4 pulmonary wedges containing metastases (upper lobe, lower lobe fissure, S6, S10) were resected on the right side. Mediastinal metastases were not resected since they were in close proximity to central vessels and bronchi.
A CT pulmonary angiogram directly after the initial V/P SPECT but preceding both metastasectomies revealed bilateral pulmonary artery compression due to bihilar metastases (Fig. 2B); however, also contrast media filling defects in segmental arteries were reported (Fig. 2A). In a follow-up 18F-FDG PET/MRI 2 months later, right hilar metastases were still visualised with intense glucose uptake, whereas left hilar metastases were partly resected (Fig. 2C). As these metastases did not show radioiodine uptake in 124I PET/CT (Fig. 2D), systemic tyrosine kinase inhibitor treatment was started. Pulmonary perfusion defects due to pulmonary artery compression by hilar metastases were finally diagnosed. Pulmonary embolism was deemed unlikely due to the left-sided post-operative normalisation, persistence of right-sided V/P mismatches and the lack of clinical symptoms.
