umbilical pilonidal sinus disease
Pilonidal sinus disease is a common problem of sacrococcygeal region. However, it is also observed in the periumbilical area.
References
Eryilmaz R, Sahin M, Okan I, Alimoglu O, Somay A. Umbilical pilonidal sinus disease: predisposing factors and treatment. World J Surg. 2005 Sep;29(9):1158-60. PMID: 16096864