Pilomatrixomas are rare, slow-growing tumors that derive from hair follicle cells, which are ectodermal in origin. They develop in the lower dermis, present as irregularly shaped, firm growths that are tethered to the overlying skin but are not, however, attached to the underlying tissue. They often cause a blue or red discoloration on the skin but are otherwise non-tender [1]. Moreover, pilomatrixomas have the ability to calcify or ossify.

They most frequently occur within the first decade of life and affect females more than males [2]. Furthermore, they are usually found in the head and neck region, but have also been reported in the upper extremities. Typically, pilomatrixomas are solitary, yet multiple growths can occur simultaneously. The occurrence of the latter may be linked to various conditions, exemplified by sarcoidosis, Gardner syndrome, and myotonic dystrophy [3].

An even rarer type of tumor is the malignant form of pilomatrixomas, that is, pilomatrix carcinoma. These may present in a similar manner to pilomatrixomas, but are distinguished by their rapid growth, and involvement of the hematologic and lymphatic systems [4]. They have a tendency to recur and sometimes metastasize.

The diagnosis of pilomatrixoma is often missed, with the correct identification of the mass being less than 30% pre-operatively [5]. The reason for the high diagnostic inaccuracy may be a combination of the rarity of the tumor, its similarity to other superficial masses such as dermoid cysts, lipomas, foreign bodies and branchial cleft cysts, and atypical features such as an uncommon location [6].

• Inguinal Lymphadenopathy

  On physical examination, the lesion was not fixed to the underlying bone and no inguinal lymphadenopathy was detected. Fine-needle aspiration was performed using a 22-gauge needle. [ijtrichology.com]

• Soft Tissue Mass

  Our hope is to increase awareness of this diagnosis for slow-growing soft tissue masses not located in the classically described locations of head and neck, explore the radiographic features on various imaging modalities, and review the current radiology [ncbi.nlm.nih.gov]

  The sonograms were retrospectively reviewed by two radiologists with more than 10 years of experience of US of soft tissue masses. The lesions were subdivided into calcified and noncalcified masses. [onlinelibrary.wiley.com]

  MRI indicated a solid soft tissue mass in the posterolateral side of the left cruris, which was observed to be hypointense in the T1A series, and hyperintense in the T2A series. [academic.oup.com]

  Pilomatrixomas are depicted on computerized tomography (CT) scans as soft tissue masses that may also contain calcifications. [symptoma.com]

• Subcutaneous Mass

  A 9-year-old boy had a subcutaneous mass on his left wrist. Ultrasound displayed a well-defined, multilobulated anechoic mass containing a few internal septa between the extensor pollicis longus and the extensor carpi radialis longus tendons. [ncbi.nlm.nih.gov]

  Turk J Plast Surg 2018;26:125-7 Introduction Pilomatrixomas are benign subcutaneous masses that originate from the hair follicle. They are often seen in the first two decades, but they can occur at any age. [turkjplastsurg.org]

  Pilomatrixoma, a common skin appendageal tumor in head and neck region, should be considered in the cytologic differential diagnoses of subcutaneous masses even in unusual locations like arm. [hindawi.com]

• Skin Discoloration

  On the physical examination, the bluish skin discoloration over the lesion so typical of PMT was overlooked. On FNA, the basaloid cells of PMT were mistaken for intermediate cells of mucoepidermoid carcinoma. [ncbi.nlm.nih.gov]

  Also, its irregular consistency, firm shape, and overlying skin discoloration are suggestive of its nature. The tumor is usually asymptomatic and grows slowly over a period of several months or years. [doi.org]

• Facial Mass

  In January 2004, a case was reported of an 8-year-old girl with 2 progressively enlarged facial masses. One of them was excised and diagnosed as pilomatrixoma. Coincidently, her 13-year-old sister had the same type of tumor when she was 4 years old. [ncbi.nlm.nih.gov]

  Case Report A 28-year-old male was referred to the department of oral and maxillofacial surgery for evaluation and management of a left facial mass. He had no other medical problems and no known food or drug allergies. [hindawi.com]

• Head and Neck Swelling

  Awareness regarding the inclusion of dermal appendage diseases is very important while establishing the differential diagnosis for chronic, painless head and neck swellings. References 1. Curran RC, Crocker J. Skin. [jscisociety.com]

• Neglect

  […] classification schemes of adnexal tumours are predominantly based on morphological and immunophenotypical similarities to adult skin structures, whereas a link between the embryology of the skin and the histogenesis of adnexal tumours has been largely neglected [ncbi.nlm.nih.gov]

  Therefore, it might be neglected in some cases. However, fast growth [ 3 ] and potential malignant transformation [ 4 ] have been reported in this benign tumor. The pilomatrixoma should be kept in mind in differential diagnosis of solid tumor. [alliedacademies.org]

The diagnosis of pilomatrixomas can be made based on clinical findings alone. The tent sign can be elicited and allows visualization of the irregularity of the mass. There is no development of lymphadenopathy. The modal location of tumors is the periorbital area, and a minority of cases are preceded by a history of trauma.

Histologically, pilomatrixomas are well circumscribed and surrounded by connective tissue. They consist of groups of metrical cells with cystic changes and central degeneration caused by ghost cells which lack a nucleus and are not exclusively found in pilomatrixomas [7]. Inflammation may be present in the surrounding tissue. Calcification occurs in the majority of tumors, whilst other changes that can occur include a local build-up of keratin, and foreign body granulomas [6].

Imaging studies are not routinely required. If X-rays are carried out, there may be visible calcifications. Pilomatrixomas are depicted on computerized tomography (CT) scans as soft tissue masses that may also contain calcifications. Magnetic resonance imaging (MRI) reveals ring-enhancing lesions, while ultrasonography may reveal peripherally hyperechoic masses with acoustic shadowing visible in the subcutaneous tissue [8].

Fine needle aspiration cytology (FNAC) remains the most accurate diagnostic test, although it also has a high margin of error [7]. On FNAC, basaloid and ghost cells are indicative of pilomatrixomas [9].

• Synovial Cyst

  cyst Digital mucous cyst Mucocele Pilonidal sinus Pseudocyst of the auricle Parasitic cyst Dermatovenerology Syphilis Gonorrhea Trichomonas vaginalis Pathology of the foreskin, phimosis, balanitis Balanitis Balanitis plasmocellularis Zoon Balanitis circinata [atlases.muni.cz]

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3. Urvoy M, Legall F, Toulemont PJ, Chevrant-Breton J. Multiple pilomatricoma. Apropos of a case. J Fr Ophtalmol. 1996;19(6-7):464-466.
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5. Julian CG, Bowers PW. A clinical review of 209 pilomatricomas. J Am Acad Dermatol. 1998;39(2 Pt 1):191-195.
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7. Wang J, Cobb CJ, Martin SE, Venegas R, Wu N, Greaves TS. Pilomatrixoma: clinicopathologic study of 51 cases with emphasis on cytologic features. Diagn Cytopathol. 2002;27(3):167-172.
8. Hwang JY, Lee SW, Lee SM. The common ultrasonographic features of pilomatricoma. J Ultrasound Med. 2005;24(10):1397–1402.
9. Agarwal RP, Handler SD, Matthews MR, Carpentieri D. Pilomatrixoma of the head and neck in children. Otolaryngol Head Neck Surg. 2001;125(5):510-515.