Benign skin tumors represent a wide category of diseases. The diagnosis is usually provided by the clinical aspect and the patient history. The pathological examination is not always considered necessary and in most cases the treatment is removal of the lesion by cryotherapy, electrosurgery or laser ablation. Deep phenotyping, including genetic and epigenetic findings, provided the basis of a new understanding of the pathogenetic mechanisms. Some benign skin tumors can be part of syndromes and the dermatologist should be aware of the extracutaneous associations defining these rare disorders: epidermal nevus can be associated with vascular malformations; nevus sebaceous can be associated with cerebral, ocular, and skeletal defects; nevus Becker is associated with cerebral, ocular, and skeletal defects; pilomatricomas appear earlier than colorectal cancer in Gardner\'s syndrome; tuberous sclerosis complex can associate not only central nervous system lesions but also pulmonary, cardiac or renal manifestations.
UNASSIGNED: Gutartige Hauttumoren kommen bei einer großen Zahl von Hautveränderungen vor. Die Diagnose wird in der Regel durch das klinische Bild und die Anamnese gestellt. Eine histopathologische Untersuchung ist nicht in jedem Fall zwingend erforderlich. Die Therapie besteht meistens in der Entfernung der Hautveränderungen durch Kryotherapie, Elektrochirurgie oder Laserabtragung. Differenzierte Phänotypisierungen einschließlich genetischer und epigenetischer Befunde liefern die Grundlage für ein neues Verständnis der pathogenetischen Mechanismen. Einige gutartige Hauttumoren können Teil von Syndromen sein, daher sollten Zusammenhänge mit nichtdermatologischen Befunden bekannt sein, die diese seltenen Erkrankungen charakterisieren. Der epidermale Nävus kann mit Gefäßmalformationen in Beziehung stehen, der Naevus sebaceus sowie der Becker-Nävus mit Defekten zerebral, okulär und am Skelett, Pilomatrixome können kolorektalen Karzinomen beim Gardner-Syndrom vorangehen, tuberöse Sklerose kann assoziiert sein nicht nur mit Veränderungen im Zentralnervensystem, sondern auch an Lunge, Herz oder Nieren.

Nevus comedonicus (NC) syndrome is a condition first identified in 1978. The cause of NC syndrome has been recently proven to be a gain-of-function, mosaic postzygotic mutation of the NEK9 gene. A systematic review of the literature retrieved 43 well-established cases of NC syndrome reported so far. Three morphological variants of NC in NC syndrome emerged: (a) the more common, predominantly comedonal type; (b) \"Selhorst type\"; and (c) \"atrophoderma vermiculatum\" type. NC syndrome is mainly associated with ocular, skeletal, and neural abnormalities, most typically ipsilateral congenital cataract and malformations of fingers and toes.

A case of nevus comedonicus syndrome with atypical cutaneous presentation (widespread involvement without any particular pattern, midline lesions involving lower abdomen and involvement of bilateral pinna), and some unusual skeletal (adduction deformity involving bilateral metatarsal along with medial deviation at the level of tarsometatarsal joint), central nervous system (agenesis of corpus callosum with a interhemispheric cyst), visceral (pancreatic cyst) and neurological manifestations have been illustrated.

Nevus comedonicus is an uncommon skin abnormality characterized by an aggregation of dilated follicular orifices filled with keratinous material. Nevus comedonicus is occasionally complicated with other conditions including cataracts, skeletal defects, central nervous system abnormalities or other extra-cutaneous diseases (nevus comedonicus syndrome). Although most cases of nevus comedonicus occur unilaterally on the face, neck and chest, the lesions occasionally show a bilateral distribution (bilateral nevus comedonicus). We report here an unusual case of bilaterally disseminated nevus comedonicus with various systemic complications. A 62-year-old Japanese man presented with a 50-year history of numerous keratotic papules and comedo-like lesions, which gradually worsened with time. Physical examination revealed that the papules were skin-colored and 1-4 mm in diameter. Some papules had dark-black keratinous materials on their surface, giving them a comedo-like appearance. The lesions were located predominantly on the face, head, neck and trunk with symmetric distribution, following Blaschko\'s lines. The patient\'s past medical history was noteworthy; he had undergone surgical treatments for thyroid cancer, pneumothorax and schwannoma in the cauda equina. He also suffered from scoliosis, cervical spondylosis and atrial fibrillation. Histopathologic examination revealed dilated and invaginated follicular structures filled with lamellar keratin, compatible with nevus comedonicus. Our patient\'s case did not fit with any previously reported diseases, and we thought a diagnosis of \"bilateral nevus comedonicus syndrome\" was the most appropriate for our patient\'s condition. He was treated with topical retinoic acid and activated vitamin D3 ointment for 3 months each, but the lesions remained unchanged.