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Koenen's tumor
Koenen's tumor
Other names	Koenen's periungual fibroma and Periungual fibroma
	Koenen tumor in patient with tuberous sclerosis complex
Specialty	Dermatology

Koenen's tumor (KT), also commonly termed periungual angiofibroma,^[1]^: 668 is a subtype of the angiofibromas.^[3] Angiofibromas are benign papule, nodule, and/or tumor lesions that are separated into various subtypes based primarily on the characteristic locations of their lesions. KTs are angiofibromas that develop in and under the toenails and/or fingernails.^[4] KTs were once considered as the same as another subtype of the angiofibromas viz., acral angiofibromas. While the literature may still sometimes regard KTs as acral angiofibromas, acral angiofibromas are characteristically located in areas close to but not in the toenails and fingernails as well as in the soles of the feet and palms of the hands.^[5]^[6] KTs are here regarded as distinct from acral angiofibromas.

KTs most commonly develop in individuals who have the rare genetic disease, tuberous sclerosis^[7] (a heritable neurocutaneous disorder^[8]) and uncommonly in individuals that do not have this genetic disease.^[9] One individual with another rare genetic disease that has similarities to tuberous sclerosis, the Birt-Hogg-Dube syndrome, has also been reported to have typical KT findings.^[10]

KTs are strictly benign (i.e. do not metastasize) but may be painful, disfiguring, and sometimes large and/or incapacitating lesions. They have often been treated by strictly local surgical resections. However, they do have a high rate of recurrence at the site of resection^[11] and therefore have been treated with various other non-invasive local measures in efforts to avoid recurrences; these other methods have also been preferred to treat numerous tumors in individuals, for cosmetic reasons, and/or to relieve tumor-induce incapacitations.^[11]^[12]

Presentation

In individuals with tuberous sclerosis, KTs commonly present with multiple firm red-colored to skin-colored nodules or tumors that emanate from the proximal nail fold or, less often, proximal skin beneath the nail. They often develop after puberty; increase in number over time; more frequently occur in the toenails than fingernails (the most common sites are on the big toe and thumb); are generally 5 to 10 mm in length but occasionally grow to far larger sizes;^[4] and may be or become disfiguring, painful, and/or incapacitating.^[13] Nearly 50% of post-puberty individuals with tuberous sclerosis have KTs.^[11] (Tuberous sclerosis is also associated with a second type of angiofibroma, adenoma sebaceum, also termed facial angiofibroma, in ~75% of cases.^[14]) Individuals presenting with KTs that do not have tuberous sclerosis commonly present with a single lesion in a nail bed.^[15] KT may also present as a recurrence of a lesion at the site where it was surgically removed.^[11] Rare cases of KTs have had a history of crushing trauma at the sites where the KTs later developed.^[4]

Pathology

Microscopic histopathological analyses of KTs commonly reveal a lesion with epidermal acanthosis (i.e. thickening of the skin), hyperkeratosis (i.e. thickening of the outermost layer of the epidermis), and skin features typical of angiofibroma viz., spindle-shaped or star-shaped fibroblasts and ectatic blood vessels in a dense collagen fiber connective tissue background.^[12]

Etiology

In cases associated with tuberous sclerosis, KTs appear to be a result of this disease's associated genetic abnormalities, i.e. loss-of-function mutations in one of the two normally paired TSC1 or one of the two normally paired TSC2 tumor suppressor genes. As a part of their functions, the TSC1 and TSC2 tumor suppressor genes act to suppress the abnormal growth of cells by contributing to the suppression of the mammalian target of rapamycin (i.e. mTOR) protein that promotes cell growth and proliferation. Inactivation of one of the TSC1 or TSC2 genes appears responsible for unleashing mTor and thereby promoting the growth of the many strictly benign lesions, including KTs, that develop in individuals with tuberous sclerosis.^[16] mTOR is inhibited by rapamycin, a drug which has been used as a topical application to successfully treat a few cases of Koenen's tumors.^[12]

A small number of cases in individuals including those that do not have tuberous sclerosis may develop KTs as reactions to local traumas.^[4]

Treatment

The treatment of KTs has varied depending on their size, numbers, locations, symptoms, damage to tissues, and disfiguring effects. Excision may be the treatment of choice for surgically accessible lesions.^[15] However, following surgical removal, KTs have a high rate of local recurrence,^[11] particularly in cases where the lesions are not completely removed.^[15] Other treatment methods, which may be used in combination with surgical removal and/or with each other include: carbon dioxide-based laser vaporization; electrocauterization; shave excision of the tumor with phenolization (i.e. excision of the tumor’s protruding portion followed by treatment of the proximal perionych [i.e., skin around a nail] with phenol to eradicate the root of the tumor);^[11] and in individuals with tuberous sclerosis, topical application of sirolimus, i.e. rapamycin, (1% solution).^[12] Some of the latter methods have been used in order to preserve the nail matrix and nailplate and may be ideal for younger patients with few tumors since they may leave a normal appearing nail.^[11]

References

^ ^a ^b Freedberg, et al. (2003). Fitzpatrick's Dermatology in General Medicine. (6th ed.). McGraw-Hill. ISBN 0-07-138076-0.
^ Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. ISBN 978-1-4160-2999-1.
^ Mocellin, Simone (2021). "57. Cutaneous angiofibroma". Soft Tissue Tumors: A Practical and Comprehensive Guide to Sarcomas and Benign Neoplasms. Switzerland: Springer Nature. pp. 189–192. ISBN 978-3-030-58709-3.
^ ^a ^b ^c ^d Oba MÇ, Uzunçakmak TK, Sar M, Serdaroğlu S (March 2021). "Dermoscopic findings in a case of multiple subungual fibromas". Acta Dermatovenerologica Alpina, Pannonica, et Adriatica. 30 (1): 35–37. doi:10.15570/actaapa.2021.8. PMID 33765756. S2CID 232366948.
^ Paral KM, Petronic-Rosic V (2017). "Acral manifestations of soft tissue tumors". Clinics in Dermatology. 35 (1): 85–98. doi:10.1016/j.clindermatol.2016.09.012. hdl:10161/13269. PMID 27938817.
^ McNiff JM, Subtil A, Cowper SE, Lazova R, Glusac EJ (July 2005). "Cellular digital fibromas: distinctive CD34-positive lesions that may mimic dermatofibrosarcoma protuberans". Journal of Cutaneous Pathology. 32 (6): 413–8. doi:10.1111/j.0303-6987.2005.00358.x. PMID 15953374. S2CID 12366680.
^ Zheng LQ, Huang Y, Han XC (May 2013). "Angiofibromas with multiple epidermoid cysts in tuberous sclerosis: new mutation or post-traumatic?". Journal of Cutaneous Pathology. 40 (5): 509–12. doi:10.1111/cup.12103. PMID 23418925. S2CID 28266318.
^ Wang MX, Segaran N, Bhalla S, Pickhardt PJ, Lubner MG, Katabathina VS, Ganeshan D (September 2021). "Tuberous Sclerosis: Current Update". Radiographics. 41 (7): 1992–2010. doi:10.1148/rg.2021210103. PMID 34534018. S2CID 237555929.
^ Longhurst WD, Khachemoune A (November 2015). "An unknown mass: the differential diagnosis of digit tumors". International Journal of Dermatology. 54 (11): 1214–25. doi:10.1111/ijd.12980. PMID 26235189. S2CID 5471149.
^ DiCicco B, Johnson W, Allred J, Soldano AC, Ramsdell WM (May 2016). "Koenen's tumor and facial angiofibromas in a case of Birt-Hogg-Dubé syndrome: A cutaneous contribution to growing evidence of a relationship with tuberous sclerosis complex". JAAD Case Reports. 2 (3): 196–8. doi:10.1016/j.jdcr.2016.03.014. PMC 4885148. PMID 27274535.
^ ^a ^b ^c ^d ^e ^f ^g Liebman JJ, Nigro LC, Matthews MS (December 2014). "Koenen tumors in tuberous sclerosis: a review and clinical considerations for treatment". Annals of Plastic Surgery. 73 (6): 721–2. doi:10.1097/SAP.0b013e31828d757d. PMID 25397697. S2CID 2048931.
^ ^a ^b ^c ^d Viswanath V, Gupte JD, Prabhu N, Gour NL (January 2021). "Multiple Koenen Tumors, a Rare Entity: Combination Treatment with 1% Topical Sirolimus Electrofulguration and Excision". Skin Appendage Disorders. 7 (1): 66–70. doi:10.1159/000511743. PMC 7879313. PMID 33614724.
^ Sobanko JF, Dagum AB, Davis IC, Kriegel DA (June 2007). "Soft tissue tumors of the hand. 1. Benign". Dermatologic Surgery. 33 (6): 651–67. doi:10.1111/j.1524-4725.2007.33140.x. PMID 17550441. S2CID 41725531.
^ Dzefi-Tettey K, Edzie EK, Gorleku P, Piersson AD, Cudjoe O (January 2021). "Tuberous Sclerosis: A Case Report and Review of the Literature". Cureus. 13 (1): e12481. doi:10.7759/cureus.12481. PMC 7854338. PMID 33552794.
^ ^a ^b ^c Hare AQ, Rich P (April 2021). "Nail Tumors". Dermatologic Clinics. 39 (2): 281–292. doi:10.1016/j.det.2020.12.007. PMID 33745640. S2CID 232311353.
^ Marom D (October 2020). "Genetics of tuberous sclerosis complex: an update". Child's Nervous System. 36 (10): 2489–2496. doi:10.1007/s00381-020-04726-z. PMID 32761379. S2CID 221018594.