Sacrococcygeal hair hiding sinus is a chronic sinus tract formed within the soft tissue of the intergluteal fissure of the sacrococcygeal region. The disease is characterized by internal hair hiding, which may manifest as a sacrococcygeal deformed cyst, which forms a chronic sinus tract after infection breaks down or heals temporarily with recurrent attacks. The disease is a rare disease, mostly after puberty 20, 30 years of age onset, male incidence is higher than female, and obese and hairy people susceptible. I. Etiology and pathogenesis There are two theories of the pathogenesis of the disease, congenital and acquired. 1, congenital theory congenital hidden hair sinus is due to the incomplete separation of the dorsal neuroectoderm and skin ectoderm during the closure of the neural tube in the third to fifth week of embryonic life. It is prone to bacterial meningitis, skin abscesses, epidural and subdural abscesses, and most often develops in infancy and early childhood, and can occur in the dorsal midline of the entire spine, with the sacrococcygeal region being the most common. 2.Acquired theory Patey and Scarf believe that the hair hiding sinus is caused by the twisting and friction of the buttocks when walking, especially in hairy males, so that the hairs between the middle hip cleft pierce into the nearby skin and form a short canal, while the hairs are still connected to their roots, the short canal is then dermatomized, and when the hairs fall off from the original hair follicle, they are inhaled by the gravitational force generated by the epithelialized short canal. Thus, the first stage is proposed to be the prickly sinus tract and the second stage is the aspirating sinus tract. The hair collects in the subcutaneous fat and becomes a foreign body, and once there is bacterial infection, a chronic infection or abscess is formed. In World War II, the incidence of the U.S. military driving jeeps was high, so it was called “jeep disease. Due to the reverse impact of the seat during the driving process, the hair between the hip fissure pierced into the nearby skin and formed. Pathology The main pathological manifestations of sacrococcygeal sinus include primary duct, sinus cavity, secondary duct and hairs. The primary duct opened in the skin and extended 3-5 cm downward with a small cavity at the end, with hairs inside the duct, sometimes sticking out of the duct, and when the specimen was opened after excision, it was found that the hairs were all free and pointed at both ends. No hair follicles, sweat glands or sebaceous glands were found at the root. Secondary ducts emanated from the deeper part and then broke upward through the skin. The ducts are covered with squamous epithelium, which is surrounded by inflammatory cell infiltration and fibrous tissue hyperplasia due to long-term recurrent infection. III. Clinical manifestations The disease is rarely symptomatic until sinus infection occurs. In typical cases, there are tiny pits in the caudal midline with fine holes in the pits; this is the primary sinus tract. The sinus opening is mostly at the gluteal groove and the direction of travel of the sinus tract is mostly towards the cranial side and rarely down towards the anal canal. Secondary sinus tracts are mostly above the mouth of the primary sinus tract, that is, “cranial side”, often slightly to one side, especially to the left side. In the resting phase, small irregular holes, about 1 mm to 3 mm in diameter, can be seen in the midline skin of the sacrococcygeal region, and the surrounding skin is red and swollen when infected, often with scarring and some visible hairs. The probe can probe into 3cm to 4cm, and when squeezed, dilute light smelly liquid can be discharged. Diagnosis and differential diagnosis 1.Diagnosis The main diagnostic sign of sacrococcygeal hair hiding sinus is acute abscess or chronic secretory sinus tract in the sacrococcygeal area, and there may be acute inflammatory manifestation locally. The hair inside is the characteristic of the caudal hair hiding sinus, but it is not the only criterion, the hair may have been discharged by itself with the pus, or it may have been discharged in the previous surgery. 20 years old, especially the healthy and hairy male youth, should consider this disease when acute abscess, hard nodes or chronic sinus tract with secretion are found in the sacrococcygeal area. 2. Differential diagnosis This disease should be differentiated from anal fistula, boils, sarcoidosis, pre-sacral teratoma and pre-sacral cystic masses with infected rupture. In anal fistula, the external opening is close to the anus, the fistula goes toward the anus, there are striae on palpation, there is an internal opening in the anal canal, and there is a history of perianorectal abscess. In contrast, the direction of travel of the hidradenous sinus is mostly cranial and rarely downward (93% travel cranially and 7% may travel around the anus below). The hypoechoic canal of the fistula extends toward the anus and is very close to or reaches the rectal cavity of the anal canal, whereas the longitudinal depth of the foci of the hairy sinus is shallower than that of the fistula, and the end of the sinus tract is farther from the anal canal and rectum, and the overall course of the sinus tract tends to be cranial. Boils grow on the skin and protrude from the skin with a golden yellow top, and canker sores have multiple external holes with necrotic tissue inside. Tuberculous granuloma is connected to the bone, with bone destruction visible on x-ray and tuberculous lesions elsewhere in the body. Syphilitic granuloma with a history of syphilis and positive syphilis seropositivity. Pre-sacral teratoma or cystic masses with infected ruptured sinus tracts have large openings, which are filled with granulation tissue, and the sinus tracts are deep and irregularly traveled. If the cystic mass is a dermatomatous cyst, there may be hair present, but in large numbers and mixed with sebum. x-ray reveals an anterior sacral space-occupying lesion with anterior rectal displacement, bone, and calcified dot shadows. V. Treatment There are many methods to treat the sacrococcygeal hair hiding sinus, but due to the high recurrence rate of this disease, there is no one of the most ideal methods widely accepted. Non-surgical injection therapy is rarely used at present due to the many complications and inaccurate efficacy. The treatment with definite efficacy is surgical excision of the hidradenous sinus and the associated inflammatory sinus tract intact. The main surgical procedures are described below. 1. Incision and drainage: When an acute abscess is formed, cross incision and drainage is performed under local anesthesia. Therefore, after the infection is controlled, if the sinus tract is small in scope, all primary and secondary ducts can be incised, granulation tissue can be removed, antiseptic and muscle-generating drugs can be applied, and second-stage healing or radical surgical treatment can be performed. 2. One-stage suturing after excision of the lesion: for patients with small sinus tracts and no infection yet, no thick fibrotic mat formation near the sinus tract opening. Contraindications: previous -stage closure; lesions more than 7.5 cm in extent; secondary exostoses 2-3 cm away from the midline; patients with too much body hair. The advantages of this method are short healing time, soft scar formed within the gluteal cleft, soft tissue between the scar and the sacrum that can tolerate injury, no effect on sitting up, and low recurrence rate (0-16%). It is currently the preferred procedure for small hidden hair sinuses. 3.Extensive excision with partial suture: It is suitable for cases with large sinus tracts, multiple ducts and more external openings. After extensive excision of the diseased tissue, the wound edges are sutured as much as possible and the central part of the wound is healed by granulation tissue. Its recurrence rate is about 5.8%, but this wooden style takes a long time to heal and forms extensive scarring. If there is an injury, the scar is prone to rupture. 4.Excision of lesion wound opening: It is suitable for those who have too large wound, recurrence after surgery or with local inflammation. The sinus tract and secondary sinus tract invasion area will be done as a whole excision, so that the wound is gradually healed by the filling of granulation tissue. The recurrence rate is low, 1.13%. 5, bag-making suture surgery: Buie and Curtiss designed this procedure, which has been more often used in recent years. The method is to remove the skin from the top of the sinus tract, clean the cavity of granulation tissue, hair and sebum, etc., and make interrupted sutures between the skin and the remaining cavity of the sinus tract. The contralateral branch sinus tracts need to be cut to the end separately and similarly pocketed. Lamb’s intestine or absorbable artificial sutures are usually used. Post-operative dressing changes are also important and are often critical to the healing of open sinuses. A fine gauze dressing is used to fill in the sinus tract. Be sure to keep the edges of the wound separate and flat and pay attention to local hygiene. When a bridging is found in the wound, it should be separated immediately with a cotton swab and the excess hair around it should be shaved frequently. Excessive granulation tissue growth can be scraped away or cauterized with silver nitrate until the wound is completely healed. Its recurrence rate is 6.9%. 6, Diamond excision and Limberg, dufourmentel flap: Intraoperatively, Melan is injected along the sinus tract in order to identify all sinus branches, and then a diamond-shaped incision is made to excise the sinus tract in its entirety. A Limberg, dufourmentel flap was performed on the right or left buttock to close the wound (the flap included the skin and subcutaneous tissue, excluding the gluteal fascia beneath it) without any intraoperative drainage, and the stitches were removed 10 days after surgery. The recurrence rate was 4.9%. 7. Asymmetric excision with intradermal suture (Karydakis procedure): A longitudinal off-center shuttle incision is made to free the subcutaneous hyperplastic granulation tissue up to the sacral fascia, and the lower part of the wound, especially the part near the gluteal sulcus, should be separated to a depth of about 4-5 cm to completely excise the diseased tissue, and the extent of excision depends on the amount of hyperplastic granulation tissue. Negative pressure suction is placed deep in the wound and the subcutaneous tissue is closed with absorbable sutures and the skin is closed intradermally with polypropylene sutures. After suturing the wound, the midline was drawn to one side and deviated by about 1.5-2.0 cm. 3rd generation cephalexin and metronidazole were given for 48 h. If there was microbial growth, antibiotic therapy was maintained for at least 5 days. Negative pressure drainage needs to be placed for 2-3 days. After performing asymmetric resection with intradermal sutures, the wound scar is drawn from the midline to the -side, flattening the gluteal sulcus and/or the posterior median sulcus. Thus the suction that could be generated locally is eliminated. Intradermal suturing is also used, avoiding the recurrence of early hair attachment due to the traditional interrupted suture method that causes the suture needle to pierce the skin several times. The procedure is uncomplicated and the complication and recurrence rate is very low (0.9%). Carcinoma of the sacrococcygeal sinus has been reported, and the lesions are mostly well-differentiated squamous cells with wound carcinoma (such as ulcers that break easily and grow faster. Wound carcinoma (e.g., ulcers that break down easily, grow quickly, bleeding and fungal-like margins) should be suspicious for carcinoma. Once diagnosed, extensive excision is performed. The 5-year survival rate is 51% and recurrence rate is 50% according to the literature.