British Journal of Radiology (2005) 78, 257-260
© 2005 British Institute of Radiology
doi: 10.1259/bjr/54676183
Pilomatrix carcinoma of the axilla: CT and MRI features
T Niwa, MD1,
T Yoshida, MD1,
T Doiuchi, MD1,
T Hiruma, MD2,
K Kushida, MD2,
A Mitsuda, MD3,
Y Kameda, MD3,
H Hayashi, MD3,
K Fujii, MD4 and
T Inoue, MD5
Departments of 1 Radiology, 2 Orthopaedic Surgery, 3 Pathology, Kanagawa Cancer Centre, 1-1-2 Nakao, Asahi-ku, Yokohama, 241-0815, 4 Depatment of Radiology, Yamato Tokusyukai Hospital, 4-4-12, Chuou, Yamato, 242-0021 and 5 Department of Radiology, Yokohama City University School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama, 236-0004, Japan
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Abstract
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Pilomatrix carcinoma, a rare malignant soft tissue tumour, is the malignant variant of pilomatricoma. We report a case of pilomatrix carcinoma of the axilla. CT demonstrated a well-circumscribed, sand-like calcified mass. MRI showed diffusely inhomogeneous, mixed signal intensities with inhomogeneous enhancements. The MRI findings were different from those previously reported for pilomatricoma.
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Introduction
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Pilomatricoma is a rare benign dermal or subcutaneous tumour originating in the hair matrix, usually located in the head or neck [1, 2]. The malignant variant of pilomatricoma, called "pilomatrix carcinoma" or "calcified epithelial carcinoma of Malherbe" is extremely rare. To our knowledge, the imaging features of primary pilomatrix carcinoma of the axilla have not been previously reported. We report the radiological findings, including CT and MRI, in a case of pilomatrix carcinoma of the axilla.
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Case report
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A 54-year-old man was referred to our institution for left shoulder pain. Plain radiograph showed soft tissue lesion with calcifications in the left axilla (Figure 1a
). The patient had not previously noticed this mass.
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Figure 1. 54-year-old man with left axillar mass. (a) Plain radiograph shows a soft tissue mass with amorphous dotted calcifications in the left axilla (arrows). (b) Coronal multiplanar reformated CT image (window width=250 HU, window level=50 HU) after administration of intravenous contrast material shows a well-circumscribed mass with multiple small calcifications and cystic components (arrows). (c) Axial T1 weighted MR image shows a diffusely inhomogeneous mass with a mixture of low signal intensity and slightly high signal intensity areas. (d) Axial T2 weighted MR images shows a mixture of high signal intensity and low signal intensity areas. ) (e) Axial T1 weighted image after intravenous administration of gadolinium contrast agent (gadopentetate dime–glumine) shows diffusely inhomogeneous enhancement (arrows).
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CT was performed after intravenous administration of contrast material and showed a well-defined, axillary soft tissue mass, 3 cm x 3.5 cm x 6 cm in size. The mass contained sand-like mottled calcifications and cystic components (Figure 1b
). To further characterize the mass, MRI examination was performed with a 0.3 T unit (MRP-7000AD; Hitachi, Tokyo, Japan). MR sequences included spin-echo T1 weighted images (repetition time (TR)= 600 ms, echo time (TE)=25 ms) before and after intravenous administration of gadolinium contrast agent (gadopentetate dimeglumine (0.5 mmol ml–1), Magnevist; Nihon Schering, Osaka, Japan), and fast spin-echo T2 weighted (TR=4000 ms, TE=117 ms, echo train length=8) images in axial and coronal planes. MRI demonstrated a well-circumscribed subcutaneous mass. Both T1 and T2 weighted images showed a diffusely inhomogeneous mass containing a mixture of low and high signal intensity areas (Figure 1c, d). Inhomogeneous enhancement was observed after intravenous administration of contrast agent (Figure 1e). No enhancement was observed in several portions of the mass. No neurovascular involvement was identified. Chest CT did not identify any metastases.
Surgical excision was performed. The excised specimen consisted of a multinodular mass in subcutaneous fat. The cut surface of the lesion showed multiple white nodules along with small calcifications and a cystic component (Figure 2a). Histological examination demonstrated nests of proliferating basaloid cells transitioning to shadow cells (Figure 2b). The tumour cells showed atypia and mitoses (Figure 2c). The cystic area contained necrotic debris. This histological pattern in association with the presence of shadow cells and increased mitotic activity led to the diagnosis of pilomatrix carcinoma.
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Figure 2. Pathological findings. (a) Cut surface of the excised specimen shows a multinodular mass with calcifications (arrowheads) and cystic components (arrows). (b) Microscopic examination shows a proliferation of basophilic cells (arrowheads) and shadow cells (arrow) (haematoxylin and eosin (H&E) x 40). (c) The tumour cells show pleomorphism, vesicular nucleus, mitoses, and prominent nucleoli (H&E x 400).
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Discussion
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Pilomatrix carcinoma is a rare malignant variant of pilomatricoma. Pilomatrix carcinomas occur more often in middle-aged to older individuals, more commonly in men, and show a predilection for the posterior neck, upper back and pre-auricular areas. The size of pilomatrix carcinoma has been reported ranging from 0.5 cm to 20 cm, with a mean of 3.95 cm, whereas that of pilomatricoma ranged from 0.5 cm to 3.0 cm [3]. The average size of these tumours is slightly larger than the size of benign pilomatrixomas [1].
To our knowledge only a few reports have described the imaging findings associated with pilomatrix carcinoma, and precise CT and MRI features of primary pilomatrix carcinoma have not been described. Venexan et al [4] reported a recurrent pilomatrix carcinoma invading the temporal bone in the post-auricular region and described the MRI findings of the tumour as containing a mixture of areas of mildly decreased signal intensity, thought to be due to the extensive calcification and scattered areas of high signal in T2 weighted images. Campoy et al [2] reported MRI findings of a recurrent pilomatrix carcinoma of soft tissue in the back invading the spinal canal at the level of the mid thoracic spine. They described the lesion as having a long T2 and intermediate signal intensity on T1 weighted images [2]. However, the report did not describe precise MRI characteristics of the tumour.
The radiological findings of a pilomatricoma typically demonstrate a well-circumscribed lesion with homogeneous or sand-like calcifications on plain radiograph and CT studies, and a homogeneous or slightly inhomogeneous mass on unenhanced and gadolinium containing contrast medium-enhanced MRI studies [5–7].
In the present case, plain radiographs and CT revealed a well-circumscribed, sand-like mottled calcified lesion, an appearance characteristic of pilomatricoma. However, MRI showed diffusely inhomogeneous areas, a finding not characteristic of pilomatricoma. Areas of low signal intensity in the T2 weighted images may correspond to calcifications, and the diffusely inhomogeneous signal intensities observed with contrast medium enhancement may relate to varying degrees of proliferating tumour. The high signal intensity areas seen in the unenhanced T1 and T2 weighted images may represent cystic spaces forming in an area of tumour necrosis.
The histological appearance of a pilomatricoma typically shows small basophilic cells with large basophilic nuclei, scant cytoplasm, and poorly demarcated cell boundaries at the tumour periphery. Transition occurs toward the centre of the mass as cells lose basophilic nuclear material and transform into shadow (ghost) cells with a central pale area and a tendency to calcify [5, 8]. Common malignant features of pilomatrix carcinoma include proliferation of hyperchromatic and vesicular basaloid cells containing numerous mitoses, necrosis in the centre of the lesion, and infiltration into fat or underlying structures [1, 8]. In the present case, the lesion contained mitoses and an area of necrosis, which are signs of malignancy. However, the tumour margin was well-circumscribed and no infiltrative changes were identified on both radiological and histological examination.
With regard to the biological behaviour of pilomatrix carcinoma, recurrence is a frequent event [8]. Wide excision should be a basic principle of treatment of pilomatrix carcinoma, which is associated with a low rate of tumour recurrence, whereas pilomatrix carcinoma recurred in more than 50% of cases in which a simple excision was performed [3]. Distant metastases are rare but have been reported in several cases. In the present case, the tumour was an incidental finding and there was no evidence of infiltration or metastasis.
In summary, we report a rare case of pilomatrix carcinoma in the axilla. Although the findings of a well-circumscribed mass and sand-like calcification are typical of pilomatricoma, the diffusely inhomogeneous MR findings with cystic changes are more suggestive of pilomatrix carcinoma.
Received for publication June 29, 2004.
Revision received September 22, 2004.
Accepted for publication November 25, 2004.
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References
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Abstract
Introduction
