Keratoacanthomas (KA) form a group of tumors of epidermal origin but whose nature remains controversial. They are thought to be low-grade squamous cell carcinomas (SCC) that may become more aggressive in immunocompromised individuals. KAs are characterized by a rapid, exophytic growth, usually followed by spontaneous regression, and they typically occur in sun-exposed areas in elderly patients.1
The subungual or periungual variant of KA is rare; it is usually locally destructive and is less likely to undergo spontaneous involution. This variant is more common in white male patients and in the fifth decade of life. The cause is still unknown, but associations have been reported with trauma, carcinogen exposure, eczema, psoriasis, atopic dermatitis, xeroderma pigmentosum, and incontinentia pigmenti.2
Case DescriptionWe present the case of a 45-year-old woman with a history of incontinentia pigmenti. She consulted for a 1-month history of a painful, rapidly growing swelling in the periungual region of the right thumb.
Physical examination revealed a skin-colored nodular lesion that occupied the ulnar and proximal borders of the nail of the first digit of the right hand (Fig. 1).
Color Doppler ultrasound was requested. The report described a solid, hypoechoic tumor with a center of lower echogenicity and of solid appearance, located at the ulnar border of the periungual region and extending into the nail bed on the same side; the ultrasound appearance was not suggestive of malignancy. The lesion measured 11mm (transverse)×10.7mm (longitudinal)x8.3mm (depth). Vascularization was predominantly peripheral, in the form of narrow vessels with low-velocity arterial flow, and there was remodeling of the surface of the underlying distal phalanx. In addition, signs of inflammatory (hypervascularity) were observed in the nail bed, and the nail plate showed changes probably of secondary dystrophic origin (Fig. 2).
Nail ultrasound in keratoacanthoma. A, Gray scale (longitudinal axis, right thumb, ulnar border) shows a hypoechoic tumor (asterisk, between+signs) with lower echogenicity centrally (o). Observe remodeling of the underlying bone surface (arrow). B, Color Doppler of the nail (longitudinal axis, right thumb, ulnar border) showing hypervascularity (in color) at the periphery of the tumor (asterisk).
The lesion was excised and histology revealed a well-differentiated, cobblestoned crateriform tumor with numerous scattered dyskeratotic cells, intralesional microabscesses, and mixed peripheral inflammation, compatible with periungual KA (Fig. 3).
Histology of keratoacanthoma. A, Well-differentiated, cobblestoned crateriform neoplasm. The numerous and clearly visible scattered dyskeratotic cells are a key to diagnosis. Hematoxylin-eosin (H&E), original magnification ×2. B, Tumor foci with mild nuclear atypia, scattered dyskeratotic cells, intratumoral microabscesses, and peripheral inflammation. H&E, original magnification ×10.
The histology report was drafted in accordance with the medical principles of the Declaration of Helsinki, and the patient gave her consent for publication.
DiscussionThis case demonstrates the usefulness of ultrasound in the diagnosis of ungual pathology, and also draws attention to the clinical signs that can lead us to suspect the presence of a tumor in the region of the nail.
Color Doppler ultrasound typically reveals a lesion with a heterogeneous ultrasound structure, with a hypoechoic border of solid appearance and an anechoic center of fluid appearance. Remodeling of the surface of the underlying bone is common.3–5
Our case presented an unusual ultrasound appearance, as the lesion was hypoechoic and had a central area of lower echogenicity, but not the anechoic fluid component typically reported.
The central region of the tumor corresponds to the keratin-filled central crater2–4; in our case, the ultrasound finding would appear to be due to a more compact central keratin mass. Ultrasound also enabled us to confirm the neoplastic nature of the lesion and to establish the differential diagnosis with other types of tumors of the nail region that present distinct ultrasound patterns, such as glomus tumor and onychomatrixoma.6,7
Glomus tumor usually presents as a solid, moderately well-defined, hypoechoic nodular lesion that provokes remodeling of the surface of the distal phalanx. The majority of glomus tumors have internal vascularization and are situated in the proximal nail bed.5,6
Onychomatrixoma has a hypoechoic appearance with hyperechoic lines or foci that affect the nail matrix and extend into the interplate space. These tumors usually have a reduced vascularity and do not tend to produce erosion or remodeling of the underlying bone surface.5–7
On ultrasound, SCC is less well defined and, rather than an anechoic or hypoechoic center, it has a heterogeneous, hypoechoic echostructure, with erosion of the nail plate and a variable degree of vascularity.5 In contrast to SCC, plain x-rays of a bone defect caused by a KA typically show well-defined borders, as KAs do not show intensely invasive behavior.3
Other imaging studies to evaluate bone involvement, apart from ultrasound, include computed tomography and magnetic resonance imaging. However, color Doppler ultrasound has been described as the method of choice as it provides the most sensitive images for the diagnosis of ungual and periungual tumors. Computed tomography and magnetic resonance imaging usually present false negatives in tumors measuring less than 3mm and poor definition of the ungual and periungual planes.6
In conclusion, when an ungual tumor is suspected, the clinical findings should be correlated with the ultrasound findings, and this should be completed by adequate histological analysis. Although the ultrasound findings were unusual in our case, color Doppler ultrasound enabled the diagnosis of a periungual tumor to be confirmed. This can favor early diagnosis and aid surgical planning.
Conflicts of InterestThe authors declare that they have no conflicts of interest.
Please cite this article as: Le-Bert M, Soto D, Vial V, Bentjerodt R, Wortsman X. Presentación ecográfica no habitual de queratoacantoma subungueal con correlación clínica e histológica. Actas Dermosifiliogr. 2016;107:442–444.
