A proliferating trichilemmal tumor (PTT) is a rare, benign, exophytic tumor originating from the isthmus region of the outer root sheath of the hair follicle. Clinically, PTTs manifest as isolated, exophytic, firm nodules that have the potential to ulcerate. These tumors may occasionally originate from a pre-existing trichilemmal cyst, or they can emerge spontaneously. Most exclusively these lesions are seen on the scalp. However, rarely these tumors can be found in other anatomical areas. Our patient had a protruding mass in her shoulder for 20 years, and this is a rare site for the occurrence of these lesions; it could be the first case to document such a site, as far as we found in the literature. The mainstay treatment of the PTT is surgical excision of the tumor, assessing the histological margins to ensure sufficient resection was made, close monitoring, and follow-up with the patient.

Pilar cysts are common benign cysts of follicular origin that typically arise in areas of skin containing dense hair follicles such as the scalp. Here we describe a unique case of a young woman who was found to have a pilar cyst on the dorsum of her hand, a rather atypical location given the relative lack of pilosebaceous units. This case illustrates the variability in pilar cyst presentation and the importance of considering a pilar cyst in the differential diagnosis of a patient presenting with a tumor of the dorsal hand.

Pilar cysts are derived from the outer layer of the root sheath of hair follicles. They were conventionally thought to arise from hair-bearing skin like the scalp. However, this notion has been refuted recently. Pilar cysts of the hand are extremely rare, with only a few case reports in the literature. We report the case of a 40-year-old male patient, with no known medical co-morbidities, who presented with a swelling over his left thumb. It was occasionally painful, and caused difficulty in grasping objects. Physical examination revealed a 2.5 x 1.5 cm swelling over the volar aspect of the thumb, at the level of the proximal phalanx. MRI revealed the presence of a well-defined cystic lesion superficial to the flexor tendons. The possibility of an epidermal cyst was considered, and the patient was advised surgery in view of his symptoms and progression in the size of the swelling. He underwent excision of the lesion along with a segment of adherent skin. Histopathological examination of the lesion revealed the presence of a pilar cyst. The patient did not have recurrence of symptoms following surgery, and was found to be doing well at the three-year follow-up. This case report urges a re-thinking of the possible origins of pilar cysts from atypical locations.

Clear cell sarcoma of the kidney is a rare renal malignancy, accounting for 2%-4% of all pediatric renal tumors. In this case report, we describe a 9-year-old boy with an asymptomatic, solitary mass on the scalp, ultimately found to be metastatic clear cell sarcoma of the kidney. This report reviews indications for imaging scalp masses to facilitate making an accurate diagnosis and treatment planning.

Trichilemmal cysts mainly occur in areas of dense hair follicle concentration. Locations include face, trunk, extremities and genitalia are less common. Prevalence and description of cases in the literature are rare in pediatric age. We report a pilar cyst removal from the upper lip with intraoral approach in an adolescent.

Pilar cysts/trichilemmal cysts are benign lesions that arise from the hair follicle epithelium. The commonest area of occurrence is the scalp but it can also occur in the head and neck region. The pilar cyst grows at a prolonged rate. They are relatively rare and occur in about 10% of the population. They appear in the region of high concentrations of hair follicles. A 75-year-old male patient came to the Department of Oral and Maxillofacial Surgery with a chief complaint of swelling on the left side of the face for the past one year. Cytological examination revealed an infected cystic lesion. Computed tomography (CT) showed a well-defined lesion in the left temporal region. After surgical excision of the lesion, it was sent for histopathological examination. Excisional biopsy revealed a pilar cyst. We report a rare case of pilar cyst in the left temporal region in a patient who was previously operated on for osteomyelitis of the left side of the mandible up to the coronoid process. These cysts may mimic temporal space infection and lead to an incorrect treatment plan.

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Trichilemmal carcinoma is a rare tumour derived from the outer root sheath of hair follicles .  It can be difficult to distinguish both clinically and histologically from other skin lesions, particularly squamous cell carcinoma.  We present the case of a 62-year-old female with a 20-year history of three 1-cm cysts on her scalp.  Over a six-month period, a cyst overlying the occiput had become painful and grown in size.  The general practitioner and subsequently local emergency department suspected infection.  The lesion was incised, and the patient was treated with oral antibiotics.  At the time of surgical excision, the lesion measured 3 x 4 cm. Microscopic examination identified rounded dermal lobules of squamous epithelium with trichilemmal keratinization, in keeping with a pre-existing pilar cyst.  There were areas with nuclear pleomorphism, mitoses and an infiltrative architecture.  A diagnosis of trichilemmal carcinoma arising in a pilar cyst was made.  Trichilemmal carcinomas are considered to be a low-grade tumour, but they have the potential to spread to lymph nodes and to metastasise to distant sites in the body, therefore adequate excision and appropriate follow-up are required.

OBJECTIVE: To determine whether ultrasound (US) could distinguish a trichilemmal cyst from a pilomatricoma preoperatively.
METHODS: Ultrasound images of 61 pathologically proven trichilemmal cysts and 90 pathologically proven pilomatricomas were analyzed retrospectively. Two radiologists evaluated several US features. The sensitivity, specificity, Youden index, and predictive values of statistically significant US features were assessed. Parallel combined tests, serial combined tests, or both were performed to identify US features with high statistical significance.
RESULTS: Results from individual US features were not satisfactory; however, serial combined tests that included absence of complete internal echogenic foci, absence of a hypoechoic rim, absence of peritumoral hyperechogenicity, and absence of vascularity showed higher diagnostic utility. The sensitivity, specificity, Youden index, positive predictive value, and negative predictive value for correctly identifying a trichilemmal cyst were 74%, 88%, 0.62, 80%, and 83%, respectively. If 1 of these 4 US features was not a match for a trichilemmal cyst, pilomatricoma was considered.
CONCLUSIONS: It may be possible to distinguish trichilemmal cysts from pilomatricomas preoperatively using US. A combined test is superior to using any individual US feature.

Epidermoid cysts with histopathologic features of human papillomavirus (HPV) infection have been previously reported and are commonly termed verrucous cysts. We report a series of eight histopathologically distinct verrucous pilar cysts, distinguished from traditional verrucous epidermoid cysts by trichilemmal keratinization, as well as two verrucous hybrid pilar-epidermoid cysts. These lesions contain characteristic stratified epithelial linings with abrupt transitions to compact eosinophilic keratin, as well as areas of papillomatosis, coarse intracytoplasmic keratohyalin granules, and vacuolar structures suggestive of HPV-induced cytopathic change. HPV-24, a β genus HPV species, was identified by degenerate polymerase chain reaction in DNA extracted from two of the lesions, and the presence of β-HPV E4 protein was confirmed by immunohistochemistry. HPV-60, the HPV species most commonly reported in verrucous epidermoid cysts, was not detected. Verrucous pilar cysts represent histopathologically and potentially etiologically distinct lesions which may be underrecognized.