Abstract: Hirschsprung’s tumor is a benign tumor occurring in the skin and is more common on the head, face and neck. It is known from the accumulation of cases, and the pathogenesis is not well understood. It occurs in adolescents, and is more common in females. It is often seen as a hard nodule on palpation, and microscopic visualization of shadow cells is the main basis for diagnosis. This tumor may recur and become cancerous. Patients with multiple trichoplasmosis may also have a family history of the disease. Surgical removal of the tumor and the tissues adhering to it is an effective treatment. Maxillofacial surgeons should be more aware of this disease to improve the diagnostic yield. Pilomatricoma (PM) is a benign tumor that occurs in the deep dermis of the skin at the junction with the subcutaneous fat and is derived from the hair matrix cells of the hair follicle. The head, face and neck are rich in hair follicles, which is a favorable site for pilomatricoma (51.9%~63% occurring in the head and neck) [1] [2] [3], but due to its diverse clinical manifestations, it can be easily confused and misdiagnosed with a variety of cysts and even parotid tumors commonly seen in the maxillofacial region (the misdiagnosis rate is quite high, sometimes up to 100%) [4], and as a result it may lead to recurrence (excision range too small) [9] or cause unnecessary damage to the patient (excision range too small) [10] or cause unnecessary damage to the patient (excision range too small). patients unnecessarily (too wide resection) [1] [4]. Therefore, it is necessary to have a better understanding of this disease.1.Nomenclature and etiology of PMMM Malherbe (1880) firstly called this hard textured skin mass as calcified epithelioma thinking it was a sebaceous gland tumor, but it was rejected by himself in 1905.In 1961, Forbis and Helwig suggested that the nomenclature be changed to pilomatrixoma (pilomatricoma), which was later changed to pilomatricoma (PM) [1].PM originates from hair stromal cells, and electron microscopy and biochemistry confirmed its differentiation to the hair cortex and the presence of citrulline within the cytosolic nesting keratins, suggesting that hair keratins can be formed; and genetic studies have revealed that mutations in the N-terminal region of cytoplasmic β-chain proteins (coded for by CTNNB1) (misconfiguration of β-chain proteins occurs in at least 75% of PMs), are the matrix neoplasia [5]. The majority of patients with PM develop the disease without conscious triggers and uncomfortable symptoms, with the exception of a few. 5 out of 355 patients (1.4%) reviewed by Hiromitsu et al [3] had experienced injuries to the site (bruises, scratches, or animal scratches) prior to the development of PM, and so some authors have suggested that mechanical irritation is a trigger for PM [6]. PM has also been reported to occur at injection entry points (0.56%), as well as in the area of chemotherapy, surgical incision sites, and foreign body invasion sites [3]. However, the root cause of PM may still be the stimulation of these sites, causing local changes in the internal environment, inducing gene mutations, which leads to hair stromal cell neoplasia. 2, morbidity Moehlenbeck et al. [2] showed that PM accounted for the same period of skin histopathology 1/824, the ratio of men and women is close to 2:3, the domestic data show that accounted for the same period of histopathology 1/20~1/1000 [4], and the number of PM in the same period of histopathology. 1000 [4], the male to female ratio is close to 1:2 [7]. All ages can develop, Moehlenbeck et al [2] reported that within 10 years of age accounted for 40.7% of the total number of cases, within 20 years of age accounted for 61%; domestic data [4] [7] show that within 10 years of age accounted for 20%, within 20 years of age accounted for 50%, that is, preferred to adolescents, but Celia [1] that the disease in the 50-60 years of age there is a high incidence period. PM has a wide range of sites, Hiromitsu et al [3] case statistics show that 41.7% occurred in the face, 30.4% of the upper limbs, head accounted for 11.6%, the neck accounted for 9.7%, the domestic data [4], [7] also shows that the head, face and upper limbs accounted for 80% of the total site of the disease, but has not been reported to occur in the palms and the abdomen, and some scholars have suggested that the growth site of PM is related to the density of hair follicles on the surface of the body. Some scholars have suggested that the growth site of PM is related to the density of hair follicles on the body surface. For example, the average density of hair follicles on the face is 705/cm2, and that of the hairy scalp is 459/cm2, but this cannot explain the difference between PM on the upper and lower limbs (the density of hair follicles is similar, but the incidence of PM on the upper limbs is 30 times more than that on the lower limbs). This tumor occurs mainly in the deep dermis at the junction with subcutaneous fat (pathology shows clear fat-encapsulated PM in only 7% of cases) [2]. There are also very few cases with a special site of development, such as under the deltoid muscle in the shoulder [8]. PM size is generally 0.5-6.0 cm, [1], and there are also reports of up to 15 cm [9]. Most of them are single, and multiple accounted for 1.37%~9.3% of the total [3] [4]. Domestic Zhang Zicheng [7] has observed 73 cases of solitary nodules, but 16.9% of them have scattered tumor nodules outside the pericardium under the microscope, which may be the histological basis of multiple PM, and there is also a report of 41 multiple PM nodules detected at one time [10]. 90% of patients with PM have no self-awareness of symptoms, and less than 3% of them have pain on palpation [3], and the swelling is mostly in the form of a nodule covered with a semi-transparent epidermis, and it can be normal skin color (80%), normal skin color (80%) and normal skin color (80%). Normal skin color (80%), red, blue, purple, light brown, etc. [11], 25% can vaguely see the white or yellow calcified spots inside. 20% of the PM is not protruding from the skin, through the palpation of the square can be touched by a hard nodule, if the skin on the taut, can be shown as “tent-like” polygonal (tentsign). There are also two special types of PM, namely, blistering PM, which is also known as lymphatic dilatation PM or loose skin PM (about 2.2%-6.3% of the total number) [3] [6]; and penetrating PM, which is often characterized by red, reddish-blue, or blackish-brown nodules, with keratinization of the skin on top, and secretion of “lime-like” granules. [12] The duration of each type of PM is 1 month to 20 years [4] [7], and the lymph nodes in the region where they are located have not been reported to be enlarged [9].The size of PM is generally proportional to the duration of the disease, but it is not absolute [5].3. Pathological characteristics Some scholars believe that most of the PMs have a complete peripheral membrane [4], but some believe that there is a clear peripheral membrane only accounted for 16.7% [7]. Some of them are as hard as stone. [7] The cut surface is mostly solid, grayish white, grayish red interspersed with grayish yellow granular material or necrosis in the center is pea-scum-like; when it is cystic, there may be reddish brown cystic fluid. Microscopically, irregular epithelial cell clusters were seen in the mesenchyme of the tumor, which mainly consisted of two kinds of cells: one kind of basophilic (present in 58% of PM), which resembled the cells of the basal layer of the epidermis and was located in the periphery; and the other kind of cytoplasmic eosinophilic, with the nucleus not coloring, and only residual shadows, which were also known as shadow cells (present in 100% of PM). The latter is necessary for the diagnosis of PM [7]. Statistically, eosinophils decrease or even disappear with the prolongation of the disease, and shadow cells gradually increase, but shadow cells are not unique to this disease, and can also be seen in certain dermatologic diseases, such as hair epitheliopathies [13]. Eosinophils are immature giant matricells-primitive germ cells that have a tendency to form irregular clusters of shadow cells, but are composed entirely of hairy cortex and may have small, rounded eosinophilic keratinized centers in the center (in 23% of PM). Shadow cells as endogenous foreign bodies often caused a foreign body giant cell reaction (83% of PM); calcification (69% – 85% of PM), ossification (15% of PM), as well as ferrous hemosiderin (25% of PM), melanin (17% of PM) were seen in the interstitium. [2] Ossification is hypothesized to be due to fibroblasts turning into osteoblasts [14] and is proportional to disease duration [7]. The tumor parenchyma and mesenchyme may also form cysts due to degeneration.4. Diagnosis, differential diagnosis and treatment of PM can be diagnosed according to the signs and clinical manifestations, but the combination of pathology is the gold standard for diagnosis. Auxiliary examination is also helpful for diagnosis. ultrasound is advantageous in determining whether it is a superficial soft tissue mass, cystic solidity, boundary, and it is more suitable for children’s parotid gland area mass to clarify the relationship with fascia (children often need general anesthesia to do CT or MRI) [15]. Radiographic plain films are of little diagnostic value for PM, and only large, calcified PMs are shown [9]. Diagnosis of PM by needle aspiration cytology is not advocated because up to 50% of PMs are misdiagnosed as malignant. [11] Clinical PM misdiagnosis is often due to the diverse manifestations of the disease, uncommon cases, scattered departments and doctors are not enough to recognize. Differential diagnosis is mainly to pay attention to the tissue origin, site of onset and appearance of some diseases similar to PM, PM is often misdiagnosed as sebaceous glands, dermatophytes (accounting for 7% of misdiagnosis), epidermoid cysts (accounting for 38% of misdiagnosis) and cysts with calcification, lipomas (accounting for 4% of misdiagnosis), dermatofibromas, lymph node nodule tuberculosis, hair root sheath cysts, malignant tumors (accounting for 8% of misdiagnosis), such as basal cell carcinoma, squamous cell carcinoma, malignant melanoma and other malignant tumors, which can be diagnosed as PM. When PM is light blue or reddish, it should be differentiated from hemangioma (5% of misdiagnosis), and when it is located in the parotid area in front of the ear, it should be differentiated from mixed tumors, etc. Vesicular PM should also be differentiated from herpetic lichen planus, vesicular fixation of drug rashes, and herpetic epidermolysis bullosa. The main points of differentiation are: etiology, relationship with parotid occlusal fascia, presence of shadow cells, infiltrative growth, and presence of cellular heterogeneity. [1] [6] [13] [16] The conventional and effective method of treating PM is to surgically excise the tumor and its adherent tissues (skin or subcutaneous tissues), and to do pathological examination so as to achieve the dual purpose of diagnosis and treatment. Regarding the scope of surgery, many scholars have only performed complete removal of subcutaneous tumors (for PM in subcutaneous cases), and almost no recurrence has been seen, so it is believed that preoperative surgery guided by the correct diagnosis can reduce the unnecessary damage to the patient [1] [4]. If the PM is adherent to the skin or surrounding tissues, invades the parotid occlusal fascia, breaks down, or is of the blistering type, more tissue excision is also necessary. PM has also been treated with CO2 laser and no recurrence has been seen after surgery. The disadvantage is that 4.1% form scars and 7.5% have pigmentary changes after surgery. Cryogenic freezing, systemic or local antimicrobial therapy is ineffective. ［Due to the limitation of the number of cases and follow-up time, the statistics of recurrence rate varies, but it is mostly less than 3% of Forbishe and Helwig’s statistics [9].PM carcinoma is clinically rare, and there were only 60 cases in the foreign literature in 1999 [17].McCulloch et al. observed a case of PM with multiple benign recurrences, and then carcinoma was found 17 years later. Hirschsprung carcinoma showed a typical PM image, but some areas of basophilic cell growth were active, with obvious heterogeneity and increased nuclear division. 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