Introduction: Despite the fact that the pilonidal cyst of the sacrococcygeal region is a long-known disease, the mechanism of accumulation or absence of hair in the cyst remains unclear, which affects the accuracy of the name of the disease, as well as understanding of its pathogenesis. Aim: Aim to perform morphological examination of pilonidal cysts of the sacrococcygeal region, to determine the nature of the cysts, the frequency of hair in the cyst cavity and to determine the causes and mechanism of its accumulation in cysts. Materials and methods: A morphological study of skin areas with altered tissues of the sacrococcygeal region after radical surgical treatment of 235 patients with a coccygeal cyst of the sacrococcygeal region was carried out. The gender distribution of patients with pilonidal cysts was as follows: 220 (93.4%) male patients, 15 female patients (6.6%). Results: Among 235 patients who underwent radical surgical treatment, the absence of hair shafts was recorded in 112 (46.8%) cases, hair in the cyst structure – in 123 male patients (53.2%), both visually and under a microscope, and in 4 of them (0.9%) only under a microscope. Among 15 patients, hair in the cyst cavity was found in 1 case (0.4%), in 14 patients they were not detected either visually or by microscopic examination. Discussion: Having observed the formation of foreign body granuloma and the accumulation of polynuclear histiocytes of foreign bodies around the hair in the pilonidal cyst cavity, a proportional increase in histiocytes depending on the number of hairs, that is, the body's reaction to the foreign body was registered. However, multinucleated histiocytes in lower numbers were also observed in cases in which hair shafts were not found either microscopically or macroscopically, which may indicate both completed phagocytosis and formation of a cyst without a hair component, registering the reaction of histiocytes to inflammatory changes in the cyst cavity. The detection of atypically located pilonidal cysts (cheek, navel) provides additional confirmation of the formation of pilonidal cyst as a result of disturbance of hair growth through the hair funnel due to inflammatory changes in the hair follicle and their accumulation subcutaneously.

Pilonidal cyst of the sacrococcygeal region is an acquired disease with the prevalence of up to 5% in the population. The overwhelming majority of patients, up to 75-80%, are males. A great number of more or less invasive methods of surgical treatment of this disease have been developed, but the results of treatment are often not satisfactory. A significant frequency of relapses of the disease, delayed healing of postoperative wounds are common. Considering the etiology and pathogenesis of this disease, a connection is visible between other pathologies: acne inversa, Hoffman's folliculitis, acne conglobata. These diseases are united by the syndrome of follicular occlusion, a condition when a lack of cytokeratin C17 leads to fragility of the sebaceous gland duct wall and inflammation of the skin tissues surrounding the hair follicle and sebaceous gland. Dermatologists successfully use retinoids, for example isotretinoin, which effectively affect the sebaceous glands, normalizing their activity and size. An integrated approach to the treatment of pilonidal cysts, an effective combination of surgical methods with a drug effect on the sebaceous glands of the skin will more efficiently solve the problem of treatment efficacy, and reduce the recurrence rate.

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