INTRODUCTION

Melanocytes are derived from the neural crest and are widely distributed throughout cutaneous and various mucosal sites. Although melanomas are typically found in sun-exposed areas of the skin in over 90% of cases (1), these tumors may less commonly arise at a number of other sites, such as the nail bed, eye, nose, or areas involving mucosal surfaces.

Given their rarity, it is not surprising that melanomas at these uncommon sites tend to demonstrate different biology compared with typical cutaneous melanomas. The v-raf murine sarcoma viral oncogene homolog B1 (BRAF) gene makes a serine-threonine protein kinase that is involved in cell division. Up to 50% of cutaneous melanomas contain mutations in the gene encoding BRAF (1). BRAF mutations are found in all melanoma subtypes but are most common in melanomas derived from skin without chronic sun-induced damage (1). Activating mutations in the v-KIT Hardy-Zuckerman 4 feline sarcoma viral oncogene homolog (KIT) gene, which controls cell division and migration, are found in 10% to 40% of melanomas involving the nail beds, palms, or mucous membranes but not as frequently as other melanomas (2,3). Guanine nucleotide-binding protein subunit alpha-11 (GNA11) and guanine nucleotide-binding protein subunit alpha q (GNAQ) genes are two genes that control cell division by increasing the activity of MAPK/ERK kinase (MEK) proteins, which in turn control cell growth, division, and movement. Abnormalities in GNA11 or GNAQ are predominantly found in melanomas involving the uveal tract (4).

In general, wide local excision, when technically feasible, offers the best chance for disease-free survival. Adjunctive radiation therapy (RT) may decrease the incidence of local recurrences in certain patients; however, no impact on survival has yet been demonstrated. RT is also an alternative to wide local excision when complete resection is not feasible. The introduction of targeted therapies and check-point inhibitors has altered the prognosis in this once dire diagnosis.

Melanomas at these unusual sites typically carry a worse prognosis than those arising in the common cutaneous locations (5–7). Earlier diagnosis is critical for proper treatment and improved survival for patients with these unusual variants. Surgeons should be aware of these atypical presentations of primary malignant melanoma, and in particular to understand the important site-specific differences in evaluation and management.

ACRAL MELANOMAS

Acral melanomas refer to melanomas involving only glabrous skin or the nail apparatus of extremities. Acral melanoma accounts for approximately 2% to 3% of all melanomas (8). It is the most common site among patients of Asian or African descent (9); in one study, 28% of acral lentiginous melanomas were found to be unpigmented (10). The pathogenesis of acral melanoma is poorly understood; however, trauma or chronic inflammation are considered possible inciting factors (11). In comparison to other cutaneous melanomas, acral melanomas have a much lower incidence of activating BRAF mutations (17%), and often have activating mutations of c-KIT (15%–40%), a type of receptor tyrosine kinase (12). Overall, acral melanomas have a poorer prognosis as compared with cutaneous melanomas with the same tumor node metastasis (TNM) stage, thought to be due to delay in the time of diagnosis (13).

Subungual Melanoma

Background

Subungual melanomas are relatively rare, arising from melanocytes in the nail matrix. They account for 0.7% to 3.5% of all melanomas (14), with 70% of cases occurring on the thumb or great toe and occuring more often in the sixth or seventh decade of life (15,16).

Evaluation

Subungual melanoma often presents as a brown or black linear streak in the nail, referred to as “longitudinal melanonychia.” In some cases, the pigment also involves the periungual skin, a finding termed as “Hutchinson’s sign.” Advanced lesions may demonstrate complete destruction of the nail.

Longitudinal melanonychia may be seen in other conditions, however, including benign nevi of the nail matrix. The lesions are more concerning when they are associated with irregular borders, ulceration, an increase in size, nail plate lifting, and extension beyond the nail bed. Subungual streaks may also be confused with subungual hematoma; however, subungual blood will move as the nail grows, while acral melanoma will remain in place.

Diagnosis

Patients presenting with a suspicious solitary, widening, irregularly shaped, or irregularly pigmented streak in the nail should undergo biopsy of the nail matrix to evaluate for melanoma (17). The technique of nail bed biopsy involves a digital block of the finger or toe, elevation of the nail plate from the nail bed, and an incisional, excisional, or punch biopsy of the lesion.

Treatment

Traditionally, the surgical treatment for subungual melanoma has been to amputate the digit at the most distal interphalangeal joint in order to preserve function whenever possible (5). However, amputation has not been shown to provide a better prognosis than conservative management of wide local excision. According to one recent comprehensive review of the literature, melanoma in situ can likely be treated appropriately with wide local excision without amputation (18); however, prospective randomized trials are lacking. Regardless of the surgical approach, preserving digital length, avoiding joint stiffness, maintaining sensation, and providing coverage must be considered for surgical planning.

If an amputation is necessary, reconstructive options include primary repair, skin grafting, and local/regional flap coverage.

Prognosis

Subungual melanomas are often locally advanced at the time of diagnosis; therefore, the overall prognosis is relatively poor. The 5-year survival rate varies considerably, from 16% to 80% (18).

Plantar/Palmar

Evaluation

Lesions on the palmar or plantar surfaces typically present as a pigmented macule or papule on the soles or palms that have an irregular border and variegated pigment (Figure 6.1). As the disease progresses, the lesions may become large, exophytic nodules. Amelanotic lesions are common and may present as pink macules or nodules. Acral melanoma of the palmar or plantar surfaces is often mistaken for other conditions, including nonhealing traumatic wounds, warts, fungal infections, pyogenic granulomas, or hematomas (19). It is therefore important to determine whether there was a history of trauma or consider a biopsy for infections not responding to appropriate treatment.

Treatment

For melanomas that arise on the sole of the foot or the palm of the hand, excision with primary closure may be very difficult to achieve given the lack of mobile skin. In some cases, skin grafts may be performed, but in some weight-bearing areas, more substantial soft tissue coverage may be required. In these cases, allowing excision of the wound to granulate, either through dressing changes or wound vacuum-assisted closure (VAC) devices, may be used. There are also a variety of rotations, advancements, or, rarely, free flaps that may be used to cover the defect. For plantar defects less than 3 cm², local flaps, like the sural flap, are typically used for weight-bearing areas, and skin grafts may be used in nonweight-bearing areas. For defects that are not amenable to closure by the aforementioned options, free flaps, like the thoracodorsal artery perforator (TDAP) flap or the anterolateral thigh (ALT) flap, may be used for reconstruction.

Figure 6.1 Acral melanoma involving the second toe.

Prognosis

After controlling for primary tumor thickness and stage, patients with acral melanomas appear to have a worse prognosis overall compared with patients with other subtypes of melanoma. The 5- and 10-year melanoma-specific survival rates for acral melanomas are 80.3% and 67.5%, respectively (8).

Melanoma of the Ear

Background

External ear melanomas are slightly less common than acral melanomas, representing approximately 1% of all cutaneous melanomas (20). The helix is the most common location for melanoma of the ear (Figure 6.2). According to one recent meta-analysis, the most common histopathological subtype is the superficial spreading melanoma (41%), followed by the nodular melanoma (22%) and the lentigo maligna (21%) (21). Melanomas involving the external ear also show a male predominance (78%) (21), usually present in their seventh decade, and often with advanced disease (20).

Figure 6.2 Melanoma involving the helix of the ear.

Treatment

Treatment options for melanoma of the ear have varied over the years from less radical forms, with preservation of the auricle (22,23), as opposed to aggressive surgery with complete auriculectomy (24). Generally, wide local excision and reconstruction are preferred in order to achieve optimal functional and cosmetic results (20,25).

There is controversy over safe excision margins in melanoma involving the ear. In general, a margin of 1 cm (21,26,27) is excised for invasive melanoma and 0.5 cm for melanoma in situ (21,28,29). External ear melanomas are typically superficial and most spread is through lateral extension rather than through the underlying cartilage (30). In a recent review article, it is recommended that the cartilage be excised in the management of malignant melanoma (31). If there is no involvement of the tumor, however, the underlying perichondrium and cartilage may be preserved for reconstruction (29,30,32–34). For melanomas ≥1 mm, Narayan and Ariyan (25) recommend cartilage excision to avoid the risk of submicroscopic residual malignant cells in the perichondrium.

There are many different ways to reconstruct defects of the ear (Table 6.1). Auricular defects are classified based on whether they are partial thickness or full thickness. For partial-thickness defects, the perichondrium should first be assessed. If the perichondrium is intact, it can be covered with a skin graft taken from the contralateral postauricular region. If the perichondrium is removed, a wedge excision can be made for defects less than 1.5 cm and pre-or post-auricular flaps may be rotated, advanced, or tunneled through cartilage into the defect.

Helical rim defects

Full-thickness defects are classified according to the location. For the helical rim, small defects (<4 cm) may be reconstructed using the Antia–Buch procedure for helical rim advancement (35). Chondrocutaneous rotation flaps may be used for defects of the middle and lower helix (36). For large defects (>4 cm), auricular cartilage grafts may be covered by a preauricular flap or staged postauricular pocket flap (37). Converse’s tunnel technique (38) is a prefabricated composite flap that is created in two stages for helical rim reconstruction, while the tubed pedicle flap from the postauricular skin or cervical skin are created and transferred in three stages. A costal cartilage graft, covered by a temporoparietal or mastoid fascia flap and a skin graft, may be needed for very large defects or when residual tissues are inadequate for reconstruction.

Middle-third defects

Small defects (<4 cm) of the middle third of the ear may be reconstructed using auricular reduction using Tanzer’s excision patterns and primary closure (38). For larger defects (>4 cm), the “flip-flop” flap or rotated postauricular island flap based off the posterior auricular artery may be used. The Dieffenbach flap (38) is another option for middle-third defects of the ear and uses contralateral auricular cartilage that is covered with a postauricular skin flap.

Lower-third defects

Lower-third defects may be covered with superiorly based flaps doubled over with subcutaneous cartilage graft for contour and support. The valise-handle technique for bipedicled chondrocutaneous flaps can be modified for lower-third defects to achieve definition of the posterior conchal wall (39).

Earlobe defects

Earlobe defects may be reconstructed using a variety of techniques. One option is the postauricular flap, which is transposed and sutured to a superiorly based anterior skin flap (40). Chondrocutaneous flaps from the postauricular surface may also be rotated inferiorly, based on a subcutaneous pedicle, in order to reconstruct the anterior surface of the lobule, while the posterior surface of the lobule can be reconstructed with a local retroauricular skin flap (41).

Prognosis

Melanoma of the external ear is associated with poorer prognosis and lower survival rates than other anatomical regions. The 5-year survival rates for stage 0, I, II, and III are 100%, 71%, 53%, and 0%, respectively. Histologic subtype (21,42) and surgical margins or type of resection (21,28,32,33) do not appear to affect survival probability.

Melanoma of the Nose

Background

Cutaneous malignant melanoma of the external nose (Figure 6.3) represents less than 1% of all cases of cutaneous melanoma (43–45). There is a paucity of literature regarding melanoma involving the external nose. In a case series from Germany, melanoma of the external nose was found to have a female predominance (64.4%) and the most frequent lesions were lentigo maligna (73.3%) (46).

Treatment/prognosis

Surgical management of melanoma of the external nose is complicated by the need to preserve function and aesthetics of the nose without compromising disease control. Currently, there are no generally accepted recommendations regarding excision margins for melanoma of the external nose (43). Excision margins are shown to range from 5 to 10 mm, with variable effects on local recurrence (32,43). Reconstruction with local/regional flaps is considered the mainstay for repair of nasal defects. Excision of the lesion should be planned with consideration of the nasal subunits (47), which allows margins of at least 1 cm to be achieved. There are many different types of reconstructive techniques that may be used for nasal reconstruction (Table 6.2). If the final aesthetic result can be improved, it may be necessary to extend the existing surgical defect to the margins of adjacent nasal aesthetic subunits. Attention should be given to ensuring proper cartilaginous support of the nose through the use of appropriate cartilage grafts or struts.

Figure 6.3 Melanoma involving the nasal sidewall and dorsum.

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