A 16-year-old, previously healthy boy, presented with an 11-month history of right popliteal fossa discomfort. This had been preceded by sudden pain in the posterior knee after falling while playing soccer. There was no effusion of the knee joint and no palpable mass. Sensory examination demonstrated no abnormalities, and deep tendon reflexes at the knee and ankle were normal and symmetric. He demonstrated mild weakness of toe flexion with normal strength of plantar flexion at the ankle. His gait was otherwise normal, and there was no evidence of meniscal or ligamentous injury.Plain X-ray and bone scan were unremarkable. Ultrasound examination revealed a cystic lesion, which was not easily compressible. Subsequent magnetic resonance imaging (MRI) of the right knee demonstrated a multilobulated tubular mass extending along the course of the distal sciatic and tibial nerves (Fig. 1). The lesion extended to the proximal tibiofibular joint. The common peroneal nerve was spared. There was evidence of denervation of tibialis posterior and flexor digitorum longus. Based on the imaging, an intra-neural ganglion was the most likely diagnosis; however, other differentials included a Baker's cyst or a peripheral nerve sheath tumour. Given the lesion was symptomatic, a decision to proceed with surgical intervention was made.A direct approach to the popliteal fossa was made via a lazy-S incision with the patient prone under general anaesthesia. Dissection revealed a grossly distended tibial nerve with a shiny fusiform appearance (Fig. 2). The epineurium was incised and a clear gelatinous fluid encountered, typical of ganglia (Fig. 3). Intra-neural dissection proceeded distally within the popliteal fossa and into the upper leg with careful preservation of the sural nerve and muscular branches. The lesion communicated with the proximal tibiofibular joint having expanded the articular branch to the joint. The lesion was divided from its origin at the joint and synovectomy of the capsule was performed. The distal tibial nerve was of normal appearance and calibre. The mass was dissected in a retrograde fashion proximally to the limit of the popliteal fossa. A cord of opaque, pale grey tissue (125 mm × 6-12 mm) was sent for histopathology. Sections showed fibrous tissue containing a multiloculated cavity without an epithelial lining with evidence of myxoid change in the stroma. Perineurial cells stained positive for epithelial membrane antigen in the outer wall of the cavity. These features were consistent with an intra-neural ganglion.The patient was reviewed regularly at 3, and then 6 monthly intervals post-operatively. He achieved restoration of full range of motion of the right leg, with only a small area of decreased sensation over the right lateral aspect of the foot, which is progressively diminishing in size.

Skin cancers in childhood are uncommon, accounting for 1% of presenting skin lesions. Risk factors for childhood skin cancer include ultraviolet exposure, hereditary factors such as dysplastic naevus or Gorlin's syndromes, or acquired factors such as radiotherapy. Often unrecognised in clinical practice is the significant risk of developing a second nonmelanoma skin cancer (NMSC) in survivors of childhood cancer. The Childhood Cancer Survivor Study cohort found a 30-year cumulative incidence of NMSC of 6.9%, of which the largest proportion occurred in survivors of Hodgkin's lymphoma (37.9%) and leukaemia (32.1%). 1The vast majority of skin cancers in childhood are identified incidentally after excision of suspect lesions. Of these, adnexal neoplasms are uncommon, and while the benign hidradenoma has been described, the malignant version, hidradenocarcinoma, has only rarely been described.2 With several pathologic subtypes described, the 'clear cell' variant is rarer still, with only one reported case in childhood identified on literature review.We report a case of clear cell hidradenocarcinoma, which highlights an appropriate approach to childhood skin lesions. A 7-year-old male, with a past history of acute myeloblastic leukaemia at age 2 with haematopoietic stem cell transplantation, presented with a slow-growing neck lesion for 18 months ( Fig. 1 -left). Initial management with topical steroids resulted in no change. Following excision, histologic examination showed a solid and cystic tumour in the dermis and subcutis, which mainly consisted of islands of basaloid cell with some peripheral palisading ( Fig. 1 -right). Prominent mitotic activity and focal necrosis were present. Occasional intracytoplasmic lumina and ducts were identified on epithelial membrane and carcinoembryonic antigen immunohistochemistry. Following external review, the features were consistent with a narrowly excised clear cell hidradenocarcinoma. A wide local excision was undertaken, with no residual tumour identified.Although malignant clear cell carcinoma is well described in adults, in childhood this tumour is exceedingly rare. In the only comparable case reported, Hernandez-Perez and CestoniParducci reported a 1-year-old infant with clear cell hidradenocarcinoma. The lesion was excised, but was multiply recurrent and presented later with metastases, and ultimately resulted in death within 6 months. 3 Other authors have described a more indolent course; however, the pathology of those lesions has been considered variants such as clear cell myoepithelioma or other adnexal neoplasms. 4 While rare, cutaneous malignancies in children can occur, with the potential for significant morbidity and mortality. A high index of suspicion, thorough pathologic assessment and appropriately aggressive management and follow-up are paramount.