Zonal mapping of sentinel lymph nodes in penile cancer patients using fused SPECT/CT imaging and lymphoscintigraphy

To define the anatomical location of sentinel lymph nodes (SLN) in penile cancer patients based on Daseler's original zonal description using a combination of single photon emission computed tomography-computed tomography (SPECT-CT), cross sectional imaging and lymphoscintigraphy and characterise the limits of Zone V.

Patients with primary penile cancer ≥T1G2 were included in the study. A total of 113 groins with impalpable inguinal lymph nodes (cN0) underwent planar lymphoscintigraphy and SPECT-CT. The sentinel lymph nodes were mapped on cross sectional imaging according to Daseler's anatomical description. Using measurements from fixed anatomical landmarks, a custom-made software program mapped the SLNs. SLNs were mapped to the previously undefined Zone V using 3 approaches to avoid observational bias: (a) as perceived by the uroradiologist, (b) limiting Zone V to a 5 mm radius from the sapheno-femoral junction or (c) using a 10 mm radius from the sapheno-femoral junction.

Using SPECT-CT, drainage to the groins was seen in 109 of the 113 cN0 groins (96.5%). The majority of the SLNs were located in the central and superior quadrants with 38.2% lying within Zone I, 45% in Zone II and 13% in Zone V. More importantly, sentinel lymph nodes were still localised to the inferior zones with 3% located in Zone III and 0.8% in Zone IV.

Using a hybrid of SPECT-CT, cross sectional imaging and lymphoscintigraphy we have demonstrated that SLNs may be located in the inferior zones. We also define the limits of Zone V as an area of 5 mm radius from the sapheno-femoral junction.