Non-invasive and minimally invasive staging of regional lymph nodes in penile cancer

The management of the regional lymph nodes in penile cancer patients, particularly when these lymph nodes are impalpable, remains controversial. Prophylactic bilateral inguinal lymphadenectomy is associated with high morbidity and is often unnecessary. However, there is no non-invasive or minimally invasive staging technique that can determine the lymph node status of penile cancer patients with 100% accuracy. We reviewed the current literature to examine the role of non-invasive and minimally invasive techniques for staging regional lymph nodes in penile cancer with particular reference to clinically impalpable disease. Cross-sectional imaging (un-enhanced CT and MRI) modalities have a role in the assessment of patients with palpable inguinal basins and in locating distant metastases, but are unreliable in staging impalpable regional lymph nodes. The spatial resolution of lymphotropic nanoparticle enhanced MRI (LNMRI) and positron emission tomography (PET)/CT are limited to several millimetres and so these modalities cannot reliably detect micro-metastases (< 2 mm). Ultrasound (US) and fine-needle aspiration cytology (FNAC) are indicated in staging palpable inguinal basins but are unreliable in isolation in the assessment of impalpable lymph nodes. They are, however, useful as an adjunct to dynamic sentinel lymph node biopsy (DSLNB) in lowering false-negative rates. While we await staging modalities that can equal the results of DSLNB with fewer disadvantages, histological staging in the form of DSLNB remains the best minimally invasive staging modality we can offer at risk patients presenting with clinically node negative groins.