Squamous cell carcinoma, subungual

Background

Subungual squamous cell carcinoma is a rare cancer of the digits (more commonly of the fingers) that usually occurs in middle-aged Caucasian men. Proposed risk factors include human papilloma virus (HPV), especially type 16, trauma, chronic inflammation, exposure to ionizing and/or solar radiation and arsenic. Clinically, it may may mimic verruca vulgaris, onychomycosis, pyogenic granuloma, nail dystrophy, exostosis, chronic paronychia, psoriasis, melanoma and keratoacanthoma. Because of this, diagnosis is challenging, often late, and occurs after failure in therapy with antifungal and antibiotics.

Imaging

On US, the lesions are heterogeneously hypoechoic with irregular margins with or without infiltration of adjacent tissues and erosions of the bone. Color Doppler US may show peripheral low-resistance pulsatile flow.

MRI features have not been well established. The lesions can be homogeneous hypointense on T1-weighted images, intermediate in signal intensity on T2-weighted images, and demonstrate heterogeneous enhancement. There may be adjacent marrow edema or frank invasion (bone invasion is seen in ~20% of cases).

Squamous cell carcinoma, subungual, MRI, MR, magnetic resonance imaging
Short-axis MR images of the thumb show a well-defined soft tissue mass that is low signal of T1-WI, high signal on T2-WI, and demonstrates avid enhancement. There is no bone marrow invasion.

Differential Diagnosis

Treatment

The treatment is surgical excision with negative margins along the total nail apparatus. However, amputation or interphalangeal disarticulation may be needed for advanced cases, especially when there is bone involvement. Sentinel lymph node biopsy is not usually part of the surgical algorithm.

References