Pilomatricoma

We present a 47-year-old male patient with an enlarging mass in the right thoracic wall for about 1 year. There was no relevant medical history and no trauma. A Computed Tomography (CT) study was requested for characterisation.

A Computed Tomography (CT) was performed without (Fig. 1a and 1b) and with intravenous contrast (Fig. 2a and 2b).
The (CT) non-enhanced images (Fig. 1a and 1b) showed a large superficial mass in the right thoracic wall. The mass was heterogeneous, predominantly hypodense with small hyperdense content, probably calcification or haemorrhagic foci.
The administration of intravenous iodated contrast agent (Fig. 2a and 2b) revealed solid (enhanced) and cystic/necrotic (non-enhanced) components. The right pectoralis major muscle had normal imaging characteristics.
The 3D reformation image revealed the macroscopic aspect of the mass (Fig. 3).
The mass had nonspecific characteristics on CT but it seemed that there was no muscle invasion.
The patient underwent surgery and the histological study was consistent with pilomatricoma (Fig. 4).

Pilomatricoma is a benign cutaneous neoplasm with differentiation of hair matrix cells [1]. It is more common in children and young adults with a second peak of onset in the 6th and 7th decades of life [1]. Pilomatricomas occur predominantly in the head and neck region, followed by the upper extremities, the lower extremities, and rarely the trunk [1].

On ultrasound studies pilomatricomas appear as superficial ovoid complex nodules that may have a heterogeneous echotexture, internal echogenic foci in scattered-dot pattern and a hypoechoic rim or posterior shadowing [2].

The computed tomography (CT) characteristics are nonspecific: subcutaneous tumours sharply demarcated with a soft tissue density, calcifications and a variable degree of enhancement [2, 3].

On MRI pilomatricomas have a homogeneous intermediate signal intensity on T1-weighted images and a heterogeneous intermediate signal intensity on T2-weighted images. The fat-suppressed T2-weighted images shows hyperintense reticulations that can also be seen on gadolinium-enhanced T1-weighted images [3]. A capsule is usually seen: hyperintense on fat-suppressed T2-weighted images and with enhancement on contrast-enhanced T1-weighted images. Peritumural subcutaneous oedema can also be present [3].

There aren no pathognomonic aspects of pilomatricomas on imaging studies, so a pathological evaluation of the lesion is necessary in order to make the diagnosis. The classic histology is the presence of ghost or shadow cells and basophilic cells.
The basophilic cells have relatively uniform nuclei and scanty basophilic cytoplasm. The shadow cells are in masses and show ghost outlines. They appear eosinophilic and may be keratinised [2, 4].
Treatment is surgical resection with wide margins of 1-2 cm. Following excision, pilomatricoma recurrences are relatively rare, with an overall rate of 2.6% [2].

Teaching points:
Pilomatricomas are cutaneous lesions more frequent in children and young adults in the head and neck region.
Pilomatricomas present as superficial tumours with nonspecific characteristics on imaging: soft tissue density and calcifications on CT, intermediate signal intensity on T1-weighted images and intermediate signal intensity on T2-weighted images.
Definitive diagnosis is made with the histhologic evaluation.