Magnetic Resonance Imaging in the Diagnosis of Onychomatricoma: A Case Report

Radiological imaging in nail unit disorders (Part I) - Modalities used

The nail unit is a unique skin appendage, capable of mounting only a limited number of reaction patterns to a variety of insults. This makes it difficult to diagnose many nail conditions based on clinical features alone. Thus, diagnostic modalities have an important role to play in nail disorders. Emphasis is placed on non-invasive diagnostic methods, of which, radiological imaging forms an important part; however, it is a field largely under-explored with very few studies and reports available in the literature. This could be due to the problems encountered in nail unit radiology including its small size, complex anatomy, requirement for special high-frequency probes to reliably evaluate superficial structures, and non-familiarity with nail unit radiological features even amongst trained radiologists. Nevertheless, it plays a useful role in diagnosing nail disorders (especially tumors), localizing the changes, exploring differential diagnoses, estimating prognosis, and planning management. This article is aimed at collating scientific data pertaining to various radiological modalities used in the diagnosis of nail diseases. The advantages and limitations of various imaging techniques used for evaluating the nail unit, including digital radiographs, high-frequency ultrasound, ultrasound doppler (USD), computed tomography (CT), and magnetic resonance imaging (MRI), are discussed in the first part. The second part will discuss the features of common and uncommon nail diseases.

Onychomatricoma Presenting as a Dystrophic Right Great Toenail: Case Report and Review

Onychomatricoma is a rare, benign nail matrix tumor. It most frequently occurs on one of the first three fingers of the dominant hand or the big toe in middle-aged women. Our patient presented with a 10-year history of a progressive thickening of her right great toenail; it bled easily and was intermittently painful. She had experienced trauma to the nail prior to the onset of the dystrophy. MRI primarily showed inflammation localized to the nail bed without bony extension. Excisional biopsy, which included both the nail plate and matrix, established the diagnosis of onychomatricoma originating from the ventral nail matrix (lunula). Nail trauma or fungal infection may have a causative role in the pathogenesis of onychomatricoma. The nail plate can show splitting, increased curvature, or ridging; it can also present with yellow, red or brown, linear, pigmented bands. The clinical differential diagnosis of onychomatricoma includes fibrokeratoma, melanonychia, onychomycosis, periungual fibroma, and squamous cell carcinoma. Dermoscopic imaging shows parallel lesion edges and splinter hemorrhages; these dermoscopic features support the diagnosis of onychomatricoma over squamous cell carcinoma. Imaging such as ultrasound or MRI may suggest the diagnosis. Biopsy of the tumor is necessary to establish the diagnosis; the tumor may derive either from the ventral nail matrix (lunula) or from the ventral surface of the proximal nail fold. Histologic features vary depending not only on tumor origin but also on tissue orientation. Proximally, there is a fibroepithelial tumor consisting of fibrous stalk pierced by epithelial invaginations; the epithelium shows matrical differentiation containing basal and prekeratogenous cells. Distally, the tumor pierces the nail plate as glove-finger digitations; these digitations appear as discrete villi in the nail plate or show their negative image as multiple empty channels that have been described as “worm holes”. The channels may be epithelial lined and contain serous fluid. It is important to obtain an adequate biopsy specimen; the distinctive fibroepithelial histology might be inapparent in partial specimens lacking the epithelial invaginations. Immunohistochemical staining can distinguish onychomatricoma from tumors that can mimic its pathologic changes: fibromyxoma, neurofibroma, and perineurioma. Complete surgical excision is generally curative.