Histological Examination
In total, 61 ICG-imaging-guided pulmonary metastasectomies were performed in these patients (1–13 operations per patient), and a total of 373 specimens were examined (Table 2).
Of these 373 specimens, 350 were ICG positive during surgery, and 23 specimens were ICG-negative (and were detected by palpation by the surgeons). Tumorous tissue was confirmed in 250 of the 350 ICG-positive specimens on microscopic examination, whereas no tumorous tissue was identified in the other 100 specimens. Tumorous tissue was confirmed in 20 of the 23 ICG-negative specimens, whereas the other 3 specimens contained no tumorous tissue. Therefore, the sensitivity of ICG imaging in detecting pulmonary metastases of hepatoblastoma was 0.93, and the positive predictive value was 0.71. Of the 250 ICG-positive and histologically tumor-positive specimens, 242 included a palpable nodule or nodules, whereas 8 had no palpable nodules.
Of the 100 ICG-positive and histologically tumor-negative specimens, 98 showed one or more histological change other than tumor. Thrombus was noted in seven specimens and osteoid or chondroid formation in eleven. These findings suggest the histological changes that occur after the regression of a metastatic tumor. Nonspecific histological changes, including fibrosis, hemorrhage, and hemosiderin pigmentation, which might not be associated with the tumor, were observed in 93 specimens (Fig. 2).
Of the 23 specimens with palpable ICG-negative tumors, 20 showed a tumorous lesion or lesions on histological examination. Most of these tumors were in patient 5, in whom the frequency of ICG-negative tumors detected increased markedly after the third operation.
The histological subtype of the metastatic lesions was epithelial type in 15 cases (predominantly embryonal type, with some mitotically active fetal subtype), and macrotrabecular type in one patient (Fig. 3A). No specimen showed the fetal type, fetal-subtype-predominant mixed fetal or embryonal type, or mesenchymal type. The ICG-negative tumors showed more-severe atypia than the ICG-positive tumors (Fig. 3B).