III.19.1 Definition
The term Unna nevus encompasses a clinical, dermoscopic, and histopathological distinctive variant of melanocytic nevus that corresponds to a papillomatous dermal or compound nevus.
The other distinct variant of compound or der- mal nevus of the face (Miescher nevus) is re- viewed Chap. III.13.
III.19.2 Clinical Features
Clinically, Unna nevus is a soft polypoid or ses- sile, usually papillomatous light- to dark-brown lesion frequently located on the trunk, arms, and neck [1, 2]. The clinical features of this com- mon type of benign dermal melanocytic nevus are often quite straightforward, allowing clini- cal diagnosis at a glance; thus, in many instanc- es dermoscopic examination is superfluous.
Nevertheless, the dermoscopic features of Unna Chapter III.19
Unna Nevus
Susana Puig and Josep Malvehy III.19
Contents
III.19.1 Definition . . . 181
III.19.2 Clinical Features . . . 181
III.19.3 Dermoscopic Criteria . . . 181
III.19.4 Relevant Clinical Differential Diagnoses . . . .183
III.19.5 Histopathology . . . .183
III.19.6 Management . . . .184
References . . . .184
nevi are very distinctive and in some atypical cases may allow a correct differential diagnosis with other benign and malignant tumors.
III.19.3 Dermoscopic Criteria
Dermoscopically, Unna nevi reveal a typical globular pattern composed of numerous tan to dark-brown, round to oval globules distributed regularly throughout the lesion, or a cobblestone pattern consisting of larger, polygonal struc- tures corresponding to big nests of nevus cells (Figs. III.19.1, III.19.2). In addition, Unna nevi in some instances display densely packed exo- phytic papillary structures (Fig. III.19.3), which are commonly separated by irregular, black comedo-like openings also known as irregular crypts, similar to those found in seborrheic ker- atosis. These exophytic papillary structures cor- respond to an exaggeration of the papillomatous surface of an Unna nevus. Sometimes, milia- like cysts and comedo-like openings are also detected by dermoscopy. The wobble sign de- scribed by Braun et al. [5] is useful to distinguish Unna nevus from seborrheic keratosis, as papil- lomatous dermal nevi wobble when the derma- toscope is pushed from site to site, whereas seb- orrheic keratoses do not wobble (see Differential Diagnosis).
When appearing as hypopigmented (light brown) or skin-colored nodules, dermal nevi reveal numerous vessels that are sometimes polymorphous. Moreover, dermoscopy usually shows, especially at the periphery, the typical
“comma-like” vessels [3, 4] which are consid-
ered typical of benign dermal nevi and some
compound nevi. These types of vessels are dif-
ferent from those seen in seborrheic keratosis.
182 S. Puig, J. Malvehy
III.19
Fig. III.19.1. Typical clinical presentation of Unna nevi on the back of a patient
Fig. III.19.2. Dermoscopy of Unna’s nevus. A globular pattern with prominent vascularization is seen.
“Comma-like” vessels are observed (insets)
Unna Nevus Chapter III.19 183
III.19.4 Relevant Clinical Differential Diagnoses
Seborrheic keratosis may be similar to verru- cous dermal nevi and dermoscopy exhibits an overlap of some of the criteria (follicular open- ings, crypts and fissures, keratin plugs, milia- like cysts). The wobble sign has been described to differentiate papillomatous seborrheic kera- tosis from dermal nevus with similar clinical appearance: In seborrheic keratosis, the tumor follows the movement of the dermoscopic de- vice (contact dermoscopy), leaving back the sur- rounding skin, but the static image of the tumor does not change, because the stiff papular com- ponent cannot be dissociated from the surface of the lesion itself. This sign occurs exclusively in seborrheic keratosis [5].
Vascularization in seborrheic keratosis shows hairpin vessels with a white halo that are prom- inent if inflammation is present, whereas in dermal nevi the presence of “comma-like” ves- sels is stereotypical [4].
Basal cell carcinomas may be similar to some dermal nevi. In basal cell carcinoma, the arbo- rizing vessels are characteristic and frequently ulceration or other dermoscopic criteria may be seen.
Melanoma sometimes mimicks a dermal ne- vus, mainly in the case of verrucous or polypoid or nevoid melanomas with poor pigmentation.
Since clinical management of Unna nevus is completely different from that of melanoma, a wrong diagnosis may lead to incorrect manage- ment (shaving biopsy, electrodissection, cryo- therapy, laser treatment) or even to excision without histopathological analyses of the speci- men. To avoid misdiagnosis of melanoma resem- bling Unna nevus, any polypoid tumor with equivocal history of changes and atypical clinical or dermoscopic findings should be considered for biopsy and histopathological examination. A traumatized Unna nevus may resemble a malig- nant tumor when inflammation or bleeding is observed. In these cases the history of trauma, the observation of typical signs in the examina- tion, and the resolution of inflammation over a short period of time confirms the diagnosis.
Other tumors and infectious diseases that could be included in the differential diagnosis of Unna nevus are warts, condilomas, fibromas, and adnexal tumors such as sebaceous epitheli- oma.
III.19.5 Histopathology
Unna nevus is a compound nevus that exhibits an exophytic structure with a markedly papil- lated silhouette. The epidermis has an epider- mal nevus or seborrheic keratosis-like pattern with elongated rete ridges which give a labyrin- thine image by merging together. Melanocytic cells are located in the core of the dermal papil- lae. A few junctional nests can be present, but it seems unlikely that Unna nevi evolves from junctional nevi. They may arise from melano- cytes that migrate along neurovascular bundles to barely reach the epidermis. Most of the le- sions have a congenital pattern if the base of the lesions is sampled, although they are considered to be acquired lesions. The dermal component of Unna nevus is restricted to the papillary layer, which is greatly expanded, and at the bottom of the tumor a well-demarcated border separates the limit between the papillary and reticular dermis.
The general symmetry of the neoplasm should not prevent the need of examination of cellular details of the lesion carefully: a nevoid melanoma can exhibit a similar silhouette.
Fig. III.19.3. Photomicrograph of an Unna’s dermal nevus exhibits an exophytic structure with a markedly papillated silhouette
184 S. Puig, J. Malvehy
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III.19.6 Management
Unna nevus is a benign tumor that does not need surgical excision. Nevertheless, in the case of inflammation, or for cosmetic reasons, they are frequently removed.
C
Core Messages
■ Unna nevus is a compound nevus that exhibits an exophytic structure with a markedly papillated silhouette.
■ Clinically, Unna nevus is a soft, polypoid, or sessile light- to dark- brown lesion frequently located on the trunk, arms, and neck.
■ Clinical differential diagnosis includes seborrheic keratosis, basal cell carci- noma, melanoma, and adnexal tumors of the skin.
■ The general symmetry of the neoplasm should not prevent the need of a careful histopathological examination of cellular details of the lesion: a nevoid melanoma can exhibit a similar silhouette.
References
1. Unna PG. Naevi und naevocarcinoma. Berl Klin Wochenschr 1893;30:14–16
2. Ackerman AB, Magana-Garcia M. Naming acquired melanocytic nevi. Unna’s, Miescher’s, Spitz’s Clark’s.
Am J Dermatopathol 1990;12:193–209
3. Argenziano G, Zalaudek I, Corona R, Sera F, Cicale L, Petrillo G, Ruocco E, Hofmann-Wellenhof R, Soy- er HP.Vascular structures in skin tumors: a dermos- copy study. Arch Dermatol 2004;140:1485–1489 4. Kreusch JF. Vascular patterns in skin tumors.Clin
Dermatol 2002;20:248–254
5. Braun RP, Krischer J, Saurat JH. The “wobble sign”
in epiluminescence microscopy as a novel clue to the differential diagnosis of pigmented skin lesions.
Arch Dermatol 2000;136:940–942
