Pearly papule at the medial canthus

Infiltrative basal cell carcinoma at the right medial canthus, treated by Mohs micrographic surgery and glabellar transposition flap with canalicular reconstruction

Learning points

• H-zone (central face, periocular, periauricular, nasal, perioral) marks the highest-risk anatomical region for sub-clinical extension and recurrence of BCC; Mohs is the preferred surgical modality for all but the smallest, well-defined, non-aggressive H-zone lesions.
• Medial canthal BCC has a particular tropism for the canalicular system (canaliculi, lacrimal sac, periosteum, medial canthal tendon) — tumour can track deep along these anatomical planes well beyond the apparent clinical margin.
• Dermoscopic features supporting BCC: arborising vessels (highly characteristic), shiny white structures, ulceration, blue-grey ovoid nests; absence of pigment network.
• Pre-operative considerations include canalicular probing / dye testing if symptomatic epiphora is present and a discussion about likely silicone intubation if reconstruction crosses the canaliculi.
• Reconstruction principles at the medial canthus: respect the medial canthal tendon, restore lacrimal function where divided, choose tissue that matches the pale, thin canthal skin (forehead / glabella) and avoid lower-lid tension.
• Glabellar transposition flap is the workhorse for small-to-medium medial canthal defects; for deeper defects involving the periosteum / canaliculi, paramedian forehead flap or full-thickness skin graft may be more appropriate.