Keywords
pilomatricoma - sebaceous cyst - ghost cell - tumor - histopathology
Introduction
Pilomatricoma is an unusual skin adnexal tumor that arises from a hair matrix derived
from the epidermal primitive basal cells, first described in 1880 by Malherbe and
Chenantais.[1] They manifest as small, firm asymptomatic nodular masses with a good prognosis.
It occurs in the head (periauricular, periorbital, frontal, and temporal) and neck
region.[2]
[3] But some unusual locations have also been documented in the literature: arm, upper
back, cymba conchae(ear), thigh, breast, sternum, and lower leg.[1]
[2]
[3]
[4]
[5] Usual lesions are less than 3 cm in size. According to the literature, pilomatricoma
with the most significant size documented was 34 × 21 cm.[6] They are usually solitary, but multiple lesions associated with Turner's syndrome
and myotonic dystrophy can be seen. Here we are reporting a rare case of giant pilomatricoma
of the chest wall, causing a diagnostic dilemma.
Case Report
A 60-year-old male patient presented with swelling over the sternum, gradually increasing
in size for 1 year. There has been a sudden increase in the size in the last 2 months
([Fig. 1A]). The swelling was polypoid with an ulcerated surface and firm to hard in consistency.
Clinically the diagnosis of the calcified sebaceous cyst was made. The MRI showed
a well-defined subcutaneous lesion with thin internal septations. Findings were in
favor of benign epidermoid cyst with secondary infection. Chest wall involvement was
not seen. Hence, wide excision was done, and the mass was 9 × 7.5 × 6 cm in size with
a cut surface showing a gray–white lesion with hemorrhage ([Fig. 1B]). Microscopy showed the dermis with a large well-circumscribed neoplasm composed
of islands of peripheral basaloid cells, abruptly transitioning into squamoid cells.
Focal shadow cells and calcification were also seen ([Fig. 2A], [2B], [2C]). Surrounding the epithelial islands, there was a mixed inflammatory infiltrate
composed of histiocytes, foreign body giant cells ([Fig. 2D]), lymphocytes, and plasma cells. No atypia or malignancy was noted. Histological
features suggested benign pilomatricoma. The patient was followed up for 1 year. No
evidence of recurrence or signs of malignancy was seen.
Fig. 1 (A) Clinical image showing polypoid growth with stalk over the sternum having an ulcerated
surface. (B) Excised sternal mass with ulcerated surface.
Fig. 2 (A, B) Histopathology showing lesion with islands of peripheral basaloid cells, abruptly
transitioning into squamoid cells (H&E, X400). (C) Histopathology showing lesion with basaloid cells and ghost cells (H&E, X400). (D) Histopathology showing lesion with foreign body giant cell (H&E, X400).
Discussion
Pilomatricoma is a rare, benign hair matrix tumor. The clinical presentations have
been noted from asymptomatic to painful tender nodules. A few lesions have presented
as bulla, discoloration, erythematous lesion, giant lesion with ulceration, and intermittent
bleeding.[1]
[2] These are slow-growing lesions but may show a sudden increase in size, as seen in
our case. Many of them will have dystrophic calcification and present as hard calcified
nodules. Due to varied clinical presentations, it is often misdiagnosed as benign
cysts to tumors. Hence, the differential diagnosis of sebaceous cyst, dermoid cyst,
retention cyst, abscess, benign vascular tumors, and adnexal tumors trichoepithelioma,
trichoblastoma, basal cell carcinoma and trichoblastic carcinoma should considered.[1]
[2]
[3]
[4]
[5] Secondary features such as inflammation and soft tissue changes in a pilomatricoma
mimic many mentioned lesions. Hence an imaging workup is useful with unusual presentations.
The role of imaging modalities in such cases is controversial. MRI on the T1 image
shows an isointense lesion in 67% of patients and hyperintense to hypointense in 76.2%
in T2. Increased uptake of fluorodeoxyglucose is seen in the positron emission tomography
scan. Calcification is detected in 81% by computed tomography, whereas USG identifies
internal echogenic foci in most cases.[3]
Fine needle aspiration cytology can also be utilized to detect pilomatricoma. The
typical central pale nuclear zone and the presence of shadow cells are distinct cytological
features but may not be present in all cases. The background may show calcium deposits,
multinucleated giant cells, basaloid, and squamous cells. Literature shows many pilomatricoma
cases are diagnosed as epidermal cysts, giant cell-rich tumors, and fibrohistiocytic
lesions.[5]
[6]
[7] Some cases may be confused with malignant lesions. This was due to high cellularity
and primitive-looking cells. The cells have a high nuclear–cytoplasmic ratio and prominent
nucleoli. Mitotic figures can be seen. Inflammatory background with the debris is
noted, mimicking tumor necrosis.[8]
[9]
Definite diagnosis is only by histopathology. It shows solid nests composed of basaloid
cells and ghost cells. There will be abrupt keratinization with the typical feature
of “ghost” or “shadow” cells. Calcification, ossification, and foreign body reactions
are commonly seen. Pigmentation and extramedullary hematopoiesis can be seen in rare
cases. Some cases show β-catenin gene mutation. It can be aggressive, indicating atypia,
recurrence, and a tendency to invade. Malignant transformation (pilomatrix carcinoma)
is rare and shows infiltrating border, atypical features, necrosis, and atypical mitosis.[10] In our case, histology showed classical features of pilomatricoma.
The treatment of choice for pilomatricoma is local excision.[11] Wide excision is done in suspected malignancy or history of recurrence or diagnostic
dilemma, assuring safety margins. In our case, it was managed with wide excision.
These tumors rarely recur unless with malignant transformation. In our case, no evidence
or features of malignancy was detected after 1 year of follow-up.
Conclusion
A giant pilomatricoma is often misdiagnosed due to its size. There are very few documented
cases occurring in the sternum. When accompanied by an unusual location and presentation
like ours, it can be easily confused with any other subcutaneous lesion. Hence, a
mandatory workup is needed before excision, keeping a rare lesion such as pilomatricoma
as one of the differential diagnoses considering the chances of pilomatrical carcinoma.
