Utility of diffusion-weighted imaging in the diagnosis of inguinal lymph node metastasis with malignant melanoma

Abstract

Malignant melanoma is a malignancy of pigment-producing cells (melanocytes) located predominantly in the skin. Nodal metastases are an adverse prognostic factor compromising long term patient survival. Therefore, accurate detection of regional nodal metastases is required for optimization of treatment. Computed tomography (CT) and magnetic resonance imaging (MRI) remain the primary imaging modalities for regional staging of malignant melanoma. However, both modalities rely on size-related and morphological criteria to differentiate between benign and malignant lymph nodes, decreasing the sensitivity for detection of small metastases. Surgery is the primary mode of therapy for localized cutaneous melanoma. Patients should be followed up for metastases after surgical removal. We report here a case of inguinal lymph node enlargement with a genital vesicular lesion with a history of surgery for malignant melanoma on her thigh two years ago. CT and diffusion weighted-MRI (DW-MRI) were applied for the lymph node identification. DW-MRI revealed malignant lymph nodes due to malignant melanoma metastases correlation with pathological findings.

Keywords: Diffusion-weighted imaging; Magnetic resonance imaging; Inguinal lymph node; Malignant melanoma; Metastasis; Apparent diffusion coefficient

Core tip: Diffusion-weighted magnetic resonance imaging (DW-MRI) measures differences in tissue microstructure based on the random displacement of water molecules. The differences in water mobility are quantified using the apparent diffusion coefficient which has an inverse relationship with tissue cellularity. As such, the technique is able to differentiate between tumoral tissue and normal or necrotic tissue. In this paper, we present an inguinal lymph node metastasis of malignant melanoma after surgery, with DW-MRI findings.