Introduction : Some liver nodules remain indeterminate despite hepatocyte-specific contrast magnetic resonance imaging (MRI) in patients with colorectal liver metastasis (CRLM).

Methods : We performed a retrospective cross sectional study of all patients who underwent liver resection for synchronous or metachronous CRLM whose MRI revealed 'indeterminate' or 'equivocal' nodules between January 2008 and October 2018.

Results : The incidence of patients with indeterminate nodules on MRI was 15.4% (60 of 389), most of whom were male (71.7%). The median age was 61 years. Synchronous lesions were found in 60% (n = 36) and solitary indeterminate nodules were found in 71.67% (n = 43). The sensitivity and specificity of IOUS for detecting indeterminate nodules were 73.68% and 93.75%, respectively, with a positive predictive value of 96.6%. Patients whose nodules were ablated were excluded from this analysis. Over half of the patients followed up had benign nodules (10/17; 58.8%). On comparing characteristics of patients with benign or malignant nodules in the follow up group, pLNR was significantly greater in patients with malignant nodules (P = 0.006). There was no significant relationship with positive lymph nodes or total number of resected lymph nodes

Conclusions : IOUS could be considered as an adjunct to MRI in patients with indeterminate nodules owing to its high positive predictive value. The pLNR could be used to help select which patients can undergo conservative therapy, at least in metachronous CRLM. Prospective studies with larger numbers of patients are needed to identify additional clinicopathological criteria for predicting the malignant potential of these lesions.