Benign,irregularly shaped shoulder mass in a pediatric patient: A case report

Abstract

Pilomatricomas are slow-growing benign skin growths seen predominantly in the head and neck region of pediatric patients. Current literature review notes that these lesions are often misdiagnosed both clinically and radiologically, as their features are non-specific, making excision and histologic evaluation the only means to confirm the diagnosis. This case report illustrates the course of a pediatric patient who presents with a pilomatricoma in a less commonly seen location. As with most of these cases, the diagnosis was unclear until surgical excision and pathology were performed.

Educational objectives

1. After reading this article, readers should be able to identify the clinical and histologic manifestations of a pilomatricoma and appreciate the importance of surgical excision for treatment.

2. After reading this article, readers should be able to formulate a differential diagnosis for an intradermal mass in a pediatric patient.

Case presentation

A previously healthy 7-year-old female presented to the general pediatric clinic for evaluation of an enlarging mass on her left shoulder. The mass, initially described by the patient as the size of two coffee beans, had been persistently increasing in size since she noticed it 1 year prior. The mass had been minimally tender with no history of known trauma to the area. The overlying skin had never appeared erythematous, inflamed, or produced any drainage. There was no impairment in the mobility of her left shoulder or arm. She had no history of similar lesions in the past, and no prior interventions were made to treat the lesion. A systemic review was otherwise normal, and she had been developing normally. She traveled yearly to China to visit family and was up to date on all vaccinations.

On physical examination, vital signs were normal. Closer inspection revealed a freely mobile nodule on the lateral surface of her left shoulder, which was grossly 2 cm in size, irregularly shaped, and appeared to have spur-like edges. There was minimal tenderness with manipulation, and the overlying skin was slightly violaceous in appearance. She had a normal range of motion of her left shoulder. An ultrasound was performed to further characterize the lesion, which demonstrated a circumscribed and mobile predominantly hypoechoic lesion without detectable flow in the subcutaneous region, consistent with benign features. The adjacent structures were visualized to be normal.

Due to the mass persistently enlarging over the past year, she was referred to pediatric surgery for further evaluation. The physical examination documented by the pediatric surgeons was similar to that previously described by the pediatrician. Given the border irregularity, the mass was hypothesized to be most consistent with a dermoid cyst versus a pilomatricoma. It was recommended to be resected due to the risk of infection or complications if the mass continued to enlarge.

Final diagnosis and outcome

The patient underwent surgical resection of the mass in its entirety via an elliptical incision. The mass, approximately 2.2 cm, was found to be hard and ovoid in shape. The final surgical pathology report confirmed a diagnosis of pilomatricoma, which is a benign mass within the dermis. The microscopic description was of a tumor composed of basaloid cells intermingled with eosinophilic shadow cells, with focal granulomatous inflammation and calcification (Figure 1).

Figure 1.

Physical examination findings: 2 cm irregularly shaped firm mass on the left upper lateral arm.

Post-resection follow-up of the patient 1 year later revealed that she has been doing well with no recurrence of the lesion.

Discussion

The patient discussed in this case presented with an intradermal mass identified as a pilomatricoma, which is also known as a calcifying epithelioma. Pilomatricomas arise from hair follicle matrix cells and were first reported by Malherbe and Chenantais in 1880. ¹ These benign skin tumors present mainly in children and women. ² The sizes of pilomatricomas can vary, but a large retrospective series found the average diameter of these lesions to be 1.2 cm. ³ These tumors can present at any age, with 60% appearing in the first two decades of life, most frequently in the head and neck region.^4,5 Pilomatricomas are known to be one of the more common solid cutaneous tumors in patients 20 years of age or younger. ²

While over half of pilomatricomas are located in the head and neck region, one study confirmed this and then went on to find that 97% of the lesions are found above the umbilicus (Figure 2). ⁶ More specifically, other common locations of presentation are the upper extremities and hair-bearing areas, such as the back and chest. ⁷ The presenting symptom, as noted with the patient in this case, is usually a solitary hard and slowly growing intradermal or subcutaneous mass. There have been reports of patients with multiple lesions as well, though this is less common. ⁴ As the lesion continues to evolve, sometimes a bluish hue or ulceration of the overlying skin can be appreciated. ⁴ A definitive diagnosis is made with surgical pathology after biopsy or resection. Histology classically shows epithelial cells in a strand-like pattern with scattered “shadow cells” throughout. ⁸ Pilomatricomas have never been documented to spontaneously regress, and surgical excision with clear margins is the treatment of choice. ² Malignant transformation has been described in the literature but is exceedingly rare.

Figure 2.

Pathology findings: Blue staining basaloid cells concentrated in the periphery with a central island of anucleate shadow cells (also known as ghost cells).

Pilomatricomas are commonly misdiagnosed clinically, with the preoperative diagnosis of pilomatricoma matching the postoperative pathology diagnosis in only 28.9% of cases. ³ Because pilomatricomas arise from the hair follicle, mimicking lesions are often those that are also of pilosebaceous origin. Pilomatricomas are most often mistaken for cystic lesions and dermoid cysts. ⁶ In the literature review, a retrospective review identified several lesions that were thought to be pilomatricomas on physical examination, but later discovered via biopsy to be an epidermal inclusion cyst, a ruptured trichilemmal cyst, and a giant molluscum contagiosum lesion. ⁹ Other common differential diagnoses cited in the literature review include a foreign body reaction, chondroma, and osteoma cutis. ⁹ High-resolution ultrasound has been used to help confirm a preoperative diagnosis of pilomatricoma, but the literature reports that this occurred in specific scenarios where the clinician already had an existing high index of suspicion for a pilomatricoma prior to imaging. The primary obstacles with ultrasound diagnosis of pilomatricomas are twofold: emerging nodules may not yet show the expected calcification, and the cystic features vary from lesion to lesion, making a standardized diagnostic approach challenging. ¹⁰ Due to this, ultrasound has not been found to be a definitive method of diagnosis, especially when the lesion appears cystic on ultrasound, as with the patient in this case, in which the radiologist commented on the lesion appearing benign but of unclear etiology due to nonspecific findings.

Conclusion

Given the indolent nature of pilomatricomas and the potential of causing local physical sequelae in the long term, such as infection or limited range of motion of the surrounding joint, prompt identification and intervention are key to successful management. In this case, the presentation was relatively classic for a pilomatricoma; however, the location being outside of the more commonly seen head and neck region made the clinical diagnosis more challenging. Pilomatricomas should be considered in pediatric patients with slow-growing, solid subcutaneous masses – especially those arising from any hair-bearing areas due to the pilosebaceous origin of these tumors.