Confused subcutaneous nodules in children: Differential diagnosis of pilomatricoma in children

Pilomatricoma is a common but easily misdiagnosed tumor in children.

hemispherical, soft mass with a hidden firm nodule beneath it on his scalp (Figure 1A).It was misdiagnosed pyogenic granuloma in the outpatient department.Total excision and histopathological examination of the lesion was performed.Before the surgery, dermoscopic examination was performed and revealed irregular white and blue structurelessness area, which settled on a red background (Figure 1B).Histopathological examination confirmed that it was a pilomatricoma (Figure 1C,D).No replase has been detected yet.

| DISCUSS ION
Pilomatricoma is a common cutaneous adnexal tumor in children.nodules, with skin-color, red, blue, or brown surface.Sometimes, it may have a pseudovesicular or penetrating appearance.Although pilomatricoma is common, it is easy to misdiagnosed. 3Because of its diverse manifestations, it is easy to be confused with other tumors, or even infection diseases.

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When the surface skin above pilomatricoma is red, it is often confused with vascular tumor, such as case 1 and case 2 in this study.Pilomatricoma is an acquired tumor with slow growth.Pyogenic granuloma is an acquired tumor with rapid growth, while infantile hemangioma occurs after birth or shortly after birth and grows rapidly at early time.In order to make a correct diagnosis, it is helpful to carry out the dermatoscopy examination.Zaballos P found that the most characteristic dermoscopic feature of pilomatricoma included reddish homogeneous areas, irregular whitish structures, dotted vessels, or linear-irregular vessels, 4 while reddish homogeneous areas surrounding by a white collarette are the most frequent finding of pyogenic granuloma. 5What's more, it is helpful to carry out ultra-high-frequency ultrasonography examination.The most common features of pilomatricoma are internal echogenic foci (calcifying) and hypoechoic rim; however, hypoechoic rim, posterior shadowing, and peritumoral hyperechogenicity were rarely observed in infantile hemangiomas. 6What's more, it should be also differentiated from infantile myofibroma which often presents as a red mass.When the surface skin above pilomatricoma is skin-color, it may be confused with epidermal cyst.In histopathology, the epidermal cyst shows a cyst deriving from epidermis or the infundibular section of the hair follicle with contents of homogeneous horny material.BCG-associated lymphadenitis is often manifested as welldefined subcutaneous nodules with calcification, which is easy to be confused with pilomatricoma.Therefore, when an infant with subcutaneous calcified nodules under the left armpit, PPD may be needed for differential diagnosis.
Treatment of these diseases is different.Although infantile myofibroma may be surgically removed, it is different from pilomatricoma in terms of operation method and resection scope.Therefore, it is important to make a correct diagnosis.Children with single subcutaneous nodule should be paid attention to distinguish pilomatricoma, vascular tumor, fibrous tumor, epidermal cyst, and BCGassociated lymphadenitis.

3. 2 | 2 3. 2 . 1 |F I G U R E 2
Case An 8-month-old boy with a pilomatricoma misdiagnosed infantile hemangioma An 8-month-old boy presented to our department with a red mass on his face for 3 months.There was no local trauma history.Dermatologic examination revealed a 1-cm-sized, red mass with a hidden firm nodule beneath it on his face (Figure2A).It had F I G U R E 1 Gross appearance, dermoscopic findings, and histopathological findings of the lesion of case 1. (A) Gross appearance: A red mass with a firm nodule beneath it.(B) Dermoscopic findings (×10): Irregular white and blue structureless areas on a red background.(C) Histopathological findings (H&E × 50): The tumor in the middle dermis is composed of basophilic cells and shadow cells, above which is dermal edema and abundant inflammatory cell infiltration.(D).Histopathological findings (H&E × 400): The tumor is composed of basophilic cells and shadow cells.Gross appearance, dermoscopic findings, and histopathological findings of the lesion of case 2. (A) Gross appearance: A red mass with a firm nodule beneath it.(B) Dermoscopic findings (×10): Irregular white structureless areas and linear vessel on a red background.(C) Histopathological findings (H&E × 50): The tumor in the middle dermis is composed of basophilic cells and shadow cells.(D) Histopathological findings (H&E × 400): The tumor in the middle dermis is composed of basophilic cells and shadow cells.been misdiagnosed infantile hemangioma.Dermoscopic examination was performed and revealed irregular white structurelessness area and dendritic vessel, which settled on a red background (Figure 2B).Total excision and histopathological examination of the lesion was performed.Histopathological examination revealed that it was a pilomatricoma (Figure 2C,D).No replase has been detected yet.

3. 3 |
Case 3 3.3.1 | A 21-month-old girl with infantile myofibroma misdiagnosed pilomatricomaA 21-month-old girl presented to our department with a red mass on her breast for 7 months, increasing rapidly (Figure3A).It had been misdiagnosed pilomatricoma.Histopathological examination was performed and revealed that the tumor showed a two-phase pattern composed of eosinophilic regions with spindle cells containing richly cellular and basophilic regions with small round or oval cells arranged around the blood vessels (Figure3B).Immunohistochemically, the tumor cells were positive for SMA (Figure3C), and negative for CK (AE1/AE3), CD68, S100, CD34, CD31, ALK, Catenin, Myogenin, Desmin, and CD99.Combined with clinical and pathological manifestations, infantile myofibroma was diagnosed.After oral propranolol, the tumor did not grow further.

3. 4 |
Case 4 3.4.1 | A 13-month-old girl with BCG-associated lymphadenitis misdiagnosed pilomatricoma A 13-month-old girl presented to our department with a nodule for 10 days.She had been vaccinated against BCG without history of tuberculosis exposure.Dermatologic examination revealed 1 cm × 1.5 cm tough, well-defined, and movable subcutaneous nodule under her armpit (Figure 4A), which had been diagnosed pilomatricoma before presenting to our department.Ultrasound was performed and showed that there was a hypoechoic nodule in the subcutaneous layer with clear boundary and multiple hyperechoic calcifications.PPD test was performed and suggested strong positive.Detection of specific T cells in tuberculosis infection (T-SPOT)was negative.Chest CT showed no abnormality.Then lymph node biopsy was performed.Histopathological examination showed lymphadenitis (Figure4B).BCG-associated lymphadenitis was diagnosed.Rifampicin and isoniazid were given.The nodule gradually narrowed.

F I G U R E 3
Gross appearance and histopathological findings of the lesion of case 3. (A) Gross appearance: A red mass on her breast.(B) Histopathological findings (H&E × 100): The tumor composed of eosinophilic spindle cells and small round or oval cells arranged around the blood vessels.(C) Immunohistochemical staining of SMA (×50): It was positive in tumor cells.

SUN
et al. upregulating hair follicle differentiation and decreasing apoptosis leads to sporadic pilomatricoma. 1 Mutations in PLCD1 from germline leading to gain-of-function of PLCδ1, which facilitates activation of PKD/ERK1/2 signaling involving in regulation of KC differentiation and proliferation, is a causative genetic defect in familial multiple pilomatricomas. 2It is characterized by soft or hard subcutaneous Histopathological examination may be done to distinguish them.Pilomatricoma shows masses composed of shadow cells and basophilic cells.The characteristic histological feature of infantile myofibroma is the biphasic pattern of growth.The peripheral plump spindle cells with tapered ends are of myofibroblastic origin.The central zone cells are more primitive, ovoid to spindle-shaped, and arranged around blood vessels in hemangiopericytoma-like pattern.This zonal pattern along with hypercellular and hypocellular areas favor a diagnosis of infantile myofibroma.