August 2013 Case 2

An 82 year-old man with right upper back lesion

Jake Fagan, MSIII, Mohammed Alnamnakani, MD, H. James Williams, MD


An 82 year old male presented to the dermatology clinic for annual follow up complaining of 2-3 week history of a new, bleeding lesion on his right upper back. There was no associated pain or itching with the lesion. On review of systems, the patient denied a history of fever or chills. He also denied any symptoms of rash or pruritis around the lesion. He had no personal or family history of skin cancer. On physical exam he was well appearing, well nourished and in no acute distress. Vital signs were within normal limits. On physical examination a 7-8 mm dome shaped pink nodule with keratotic core was noted on the upper right aspect of his back. No other rash or erythematous areas were seen. A shave biopsy of the lesion was performed.

Gross Description

A shave biopsy of skin from the right upper back was received measuring 1.2 x 1.1 x 0.2 cm. There was a 0.8 x 0.7 cm raised lesion located 0.1 cm from the nearest margin with a 0.2 x 0.2 cm area of brown discoloration. The lesion appeared to be inferior to the epidermis and was well demarcated from the surrounding tissue.

Figure 1:Low power view of shave biopsy. Lesion lies deep to the epidermis and is well demarcated from the surrounding soft tissues.
Figure 2:Sharply demarcated cystic lesion with peripheral basophilic cells and central eosinophilc cells is seen deep to the epidermis.
Figure 3:Transition from basophilic cells to eosinophilic nuclei depleted "shadow cells".
Figure 4:Transition from peripheral basaloid cells to central keratinized, eosinophilic "shadow cells".
Figure 5:"Shadow cells" consisting of keratinized benign squamous cells are evident within the center of lesion.


What is the diagnosis ?


Please select an answer above.


Pilomatricoma (PM) is a rare benign skin tumor that is difficult to diagnosis clinically. Only 46% of pre-operative diagnoses are made correctly.[1] This skin lesion was first described by Malherbe and Chenantais in 1880 as a "calcifying epithelioma".[1,2,4] The term pilomatrixoma was first used by Forbis and Helwig in 1961 and changed to pilomatricoma in 1977.[1,4] These benign skin tumors present clinically as a slowly growing and mobile, rock-hard, subcutaneous masses that range in size from 0.5 to 5 cm.[1,3,4] The lesion is often misdiagnosed clinically as a basal cell carcinoma, squamous cell carcinoma, or sebaceous cyst. PMs account for 1 - 1.5% of all benign skin tumor lesions and appear to be bimodal in their age distribution with 50% occurring in the first two decades of life, and another increase in occurrence in the sixth decade of life.[3] Although found on any part of the body, there is a predilection for the neck, maxillofacial area and eyebrow while sparing the palms and soles of the feet.[3, 4] Due to the increased incidence in the maxillofacial area, dental healthcare professionals must be aware of these lesions.

Tumors are well circumscribed and are encapsulated by a fibrovascular connective stroma. The peripheral cell layer is derived from basaloid, matrix cells that fail to progress to differentiate into hair follicles.[1,3,4] These cells contain small amounts of cytoplasm and large, hyperchromatic nuclei.[1] These peripheral basophilic cells are highly mitotic with indistinguishable cell borders.[1] As the basaloid cells mature, they keratinize and move toward the center of the PM. During this progression, they lose their nuclei by karyolysis and form "shadow cells".[1] These shadow cells make up the center of the PM and take on an esoinophilic appearance.[1,3,4] As the tumor ages, shadow cells increase in number. Most lesions contain varying amounts of calcifications/ossifications throughout the PM.[4]

Genetic mutations in the Beta-catenin protein (CTNNB1 gene) have been studied with respect to PMs.[1,5] This protein has many functions related to cellular junctions an signal transduction, and it functions as a transcription factor for c-myc and cyclin-D1 in cellular proliferation of the hair follicle.[5] Mutations in the Beta-catenin gene have been found in 75-100% of human PMs.[5] This is important in confirming the diagnosis as there has been no link to this gene in other hair cell tumors.[5]

Diagnosis is primarily by clinical inspection, but due to the high pre-operative misdiagnosis, histological studies is necessary to confirm clinical suspicion.[1] The "Tent sign" is a diagnostic test done by stretching the skin over the mass allowing the irregular, often calcified, surface of the PM to become apparent.[6] Radiology is of little diagnostic value and is used mainly to distinguish between pre-auricular and parotid gland location.[4] X-ray and CT show small areas of signal dropout that are consistent with calcifications found within the tumor. CT can be used to assist in removal of a PM in areas such as pre-auricular.[3,4] In a series of fine-needle aspirations (FNA) of this tumor, cytologic diagnoses were correct in only 44% (11 out of 25 cases) as the specimen did not contain certain morphological features needed for diagnosis.[7] Reports also show that FNA can lead to an increase in the rate of false positives for PM.[8]

Treatment of PM is accomplished by simple tumor excision.[3,4] Recurrence may occur and is most likely due to incomplete removal during excision (occurring in 2-6% of all cases).[3] Malignant transformation of PM is very rare; fewer than 80 cases are reported worldwide.[4] Indicators of PM carcinoma are cellular pleomorphism, atypia, central necrosis, and infiltration of soft tissue and vasculature. Increase in mitoses, although often seen in PM carcinoma, is not a distinguishing feature as it is a common finding in benign PM.[1]


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  2. Malherbe A, Chenantais J. Note sur l' epithelioma calcife des glandes sebacees. Prog Med (Paris) 1880;8:826-8
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  9. Seili-Bekafigo I, Jonjić N, Stemberger C, Rajković-Molek K. Additional cytomorphological criteria in diagnosis of pilomatricoma--benign tumor with bad reputation.Coll Antropol. 2010;34(1):117–122.