According to recent findings, the pilonidal sinus is an acquired condition, and a previously discussed congenital cause now seems unlikely.
The following factors are considered predisposing in its development: male gender, obesity, heavy hair growth in the natal cleft, poor hygiene, sedentary activities, a deep gluteal cleft, positive family history.
Hair plays a special role in this context: F. Stelzner demonstrated as early as the 1980s that hairs, fixed on small barbs, penetrate the skin. Another indication that hair plays a significant role is the fact that pilonidal sinus is unknown in China, as Chinese people do not have hair in the natal cleft.
In their latest updated form from 2014, the guidelines of the German Society for Coloproctology recommend surgery as the treatment method of choice. The abscess is initially widely unroofed to allow effective drainage. The definitive treatment of the pilonidal sinus is then performed electively in one of the following two ways:
- Excision with secondary wound healing or
- Excision with primary wound closure (only in an infection-free stage!) → after excision, the wound is primarily closed with sutures, possibly with plastic reconstructive care.
The local or systemic administration of antibiotics is to be rejected, as they do not result in definitive healing of the sinus. The injection of phenol solution is obsolete due to its high toxicity and possible absorption of phenol.
There is no spontaneous healing. An asymptomatic pilonidal sinus persists for life but can also progress to the acute (abscessing) form or the chronic stage. After prolonged existence, malignant transformation is possible. Davis et al., Kulaylat et al. found more than 40 such cases by 1966; in 80% it was a squamous cell carcinoma.
After excision, secondary wound healing is not significantly more effective than primary wound closure regarding recurrence. All studies show a tendency towards a low recurrence rate after secondary wound healing, but significance was never achieved.
There is a common belief that open wound treatment leads to a lower recurrence rate. The theory here is that a stable scar forms, and thus no recurrence can occur in the hairless scar tissue. This theory cannot be substantiated by the literature. Allen-Mersh already showed in his 1990 review that open wound treatment is associated with an average recurrence rate of 13%. Doll and colleagues recently demonstrated an actuarial recurrence rate of 22% after a follow-up period of just under 15 years.
The excision of the pilonidal sinus should generally be complete. Typically, the excision of the granulation tissue is carried out close to the sacral fascia. However, there is no clear indication in the literature that the periosteum should be touched. In contrast, it must be assumed that excision of the periosteum with denudation of the sacrum increases postoperative pain.
To ensure complete excision, marking the foxhole-like inflammatory tissue with methylene blue is recommended. Doll and colleagues were able to show that the use of methylene blue has a significant impact on the recurrence rate.
A primary median wound closure after excision of a pilonidal sinus is associated with high postoperative morbidity and recurrence rate. The frequency of wound healing disorders reaches a rate of 30% or more in the case of primary median wound closure.
For open wound treatment, a healing time of over 3 months is not unusual. Open wound treatment does not represent an optimal alternative due to the prolonged postoperative treatment phase and the socioeconomic burden. Surgical methods that avoid the formation of a median wound and lead to flattening of the gluteal cleft appear sensible and lead to better short- and long-term results.
As early as 1973, Karydakis reported on the results of a new surgical method he developed for treating a pilonidal sinus. The surgical principle was based on the pathogenesis of the disease postulated by the author.
The axis of the elliptical skin incision should lie 2–3 cm lateral to the midline on the side where the disease is more pronounced. The fistula openings in the natal cleft (primary pore or primary pores) must be excised, but the secondary fistula openings can be left if they are outside the excision area. Around the secondary fistula opening, a conservative excision of the skin is sufficient. After marking the incision line, the skin is excised with the subcutaneous fat tissue. The thickness of the resectate should not exceed 1 cm, as the resulting defect would otherwise be too large and difficult to close. On the opposite side, a flap is mobilized, including the subcutaneous fat tissue, with a width of 2–3 cm and a thickness of 1 cm. With a series of absorbable sutures of size 2-0, the flap is grasped at its lateral edge and sewn precisely to the midline. The sacral fascia or the capsule of the pilonidal sinus forms a firm suture bed in the midline. A suction drain is placed to prevent hematoma formation. This is followed by a subcutaneous suture line and the skin suture.
The recurrence rate reported by Karydakis in over 6000 operated patients was less than 1%, and the postoperative morbidity, mostly superficial wound infections, was less than 10%. The good results with the Karydakis operation were later repeated by other authors. Potential criticisms of the Karydakis operation include the cosmetic change of the buttocks and the occurrence of paresthesias. The procedure largely flattens the natal cleft. Especially in women, this change must be discussed with the patient before the operation. Paresthesias in the area of the flap occur frequently and sometimes persist for more than a year. However, this does not burden the patients.
A systemic preoperative antibiotic prophylaxis does not seem to affect the wound healing process. This was shown in the prospective randomized study by Sondenaa. Other reports also confirmed this observation. The significance of postoperative antibiotic prophylaxis after performing a procedure with asymmetric wound closure (e.g., Karydakis operation) or after flap plasty is still unclear. Some authors report a positive effect of postoperative antibiotic therapy (ciprofloxacin, cefuroxime, or metronidazole for 4–5 days) on the frequency of postoperative wound healing disorders. However, the advantage of postoperative antibiotic therapy in terms of wound healing is not scientifically proven.
The skin sutures should be left in place for at least 14 days. A general recommendation for bed rest immediately after surgery is not evidence-based. Nevertheless, patients should be advised to maintain light bed rest in the first few days after surgery and to avoid heavy physical activities in the first weeks after suture removal.
The depilation is theoretically supposed to reduce the recurrence rate. However, it has long been known that mechanical hair removal using blade shaving offers no advantage. Stirnemann and Blasimann already showed in 1983 that the recurrence rate cannot be reduced by mechanical shaving. A Bundeswehr cohort study from 2009 showed the same effect, whereby mechanical shaving even favored recurrence formation (Petersen 2009). Hair removal without creating additional broken hair remains a promising treatment option for preventing recurrence. Therefore, other hair removal methods will have to prove their effectiveness. Foremost among these is laser epilation. At least 5 sessions are required for complete hair removal in the natal cleft. Afterward, the natal cleft remains permanently less hairy.