Transillumination: shining a light from within.

To cite: Irfan M, Waldron R, Bolger J, et al. BMJ Case Rep Published online: [please include Day Month Year] doi:10.1136/ bcr-2014-207910 DESCRIPTION Thorough examination of a scrotal mass includes transillumination. By holding a light externally to the scrotum, one can easily determine whether the mass is cystic (light shines through) or solid (light blocked by the mass). At first glance, figure 1 is likely to be interpreted as a transillumination test to confirm the presence of hydrocele. More careful inspection confirms the peripheral location of the examiner’s gloved hands and the absence of an external light source. Where is the light source located? This image was observed during limited colonoscopy performed in a 74-year-old man with long-standing left inguinoscrotal hernia and a recent history of altered bowel habits. Colonoscopy was limited to 35 cm due to the presence of an incarcerated loop of sigmoid colon. The light source is therefore located at the level of the mid-sigmoid colon, which in turn is located within the scrotal component of the hernial sac. There have been 16 cases reported to date in the world literature documenting anatomical difficulties encountered during the performance of colonoscopy in patients with significant amounts of colon incarcerated within right or left inguinoscrotal hernias. We believe that this image captures a rare phenomenon, a unique variant of the transillumination test.