An Enlarging Mass Superimposed on a Giant Congenital Melanocytic Nevus: A Case Report and Review of Literature

ABSTRACT

Congenital melanocytic nevi (CMN), arising from the proliferation of melanocytes, manifest at birth and are colloquially termed as bathing trunk, coat‐sleeve, or stocking nevi. These lesions, occurring in approximately 1 to 2% of neonates, predominantly localize over the trunk and thigh regions. Giant congenital nevi, characterized by a size exceeding 20 cm, often present with pigmentation and hairiness. Herein, we present the case of a 14‐year‐old patient diagnosed with a giant congenital nevus (bathing trunk nevus) accompanied by lipomatosis, while concurrently reviewing the literature to delineate this rare association. Our investigation identified a total of six cases, comprising five females and one male. Notably, half of the cases (3/6) exhibited multiple lipomatous lesions, with the back region emerging as the most prevalent site. In our presented case, progressive enlargement of a soft tissue mass in the right flank prompted excision, revealing a well‐circumscribed lipomatous lesion infiltrated diffusely by benign‐appearing melanocytes within fat lobules, as confirmed by immunohistochemistry. Specifically, positivity for HMB45 and S100 markers was observed. Beyond the rarity of such occurrences, our report underscores the infrequent concomitance of CMN with lipomatosis.

Summary.

• Lipomatosis is a rare association with congenital melanocytic nevus (CMN) that suggests a potential underlying genetic or developmental link, particularly in individuals with multiple or large CMNs.

• This co‐occurrence warrants careful clinical monitoring for potential complications, including the risk of malignancy and other related systemic conditions, emphasizing the need for vigilant surveillance.

1. Introduction

Congenital melanocytic nevi (CMN) are defined as benign melanocytic proliferations, affecting approximately 1% to 2% of newborns, with a higher prevalence observed among Asian and Black children [1, 2]. Manifesting either at birth or within subsequent weeks, these nevi typically manifest as light brown to black patches or plaques, varying in size and distribution across the body. Classification commonly stratifies CMN into small (< 1.5 cm), medium‐sized (1.5 to 19.9 cm), and large or giant (20 cm or greater) lesions [3, 4]. Described as ‘garment or bathing trun’ nevi, large lesions are infrequent, with an incidence ranging from 1:200,000 to 500,000 births and a notable female predilection [3]. They are often deeply pigmented, accompanied by moderate hair growth, and frequently associated with scattered satellite lesions. While the hairy component, present in 95% of cases, tends to become more prominent in late childhood, the nevus itself typically pales at this stage [1].

Giant nevi may exhibit associations with several comorbidities, including neurocutaneous melanosis, diffuse lipomatosis, structural brain malformations, skull bone hypertrophy, limb atrophy, skeletal asymmetry involving soft tissue hyper‐ and hypoplasia, von Recklinghausen's disease, and vitiligo [5]. The likelihood of neoplastic transformation is directly proportional to CMN size, with an estimated incidence ranging from 6% to 12% over one's lifetime [6]. The emergence of firm nodules requires careful attention, with differential diagnoses encompassing proliferative nodules and malignant melanoma [4]. Malignant transformation within giant CMN predominantly occurs in axial locations, with extremity lesions presenting lower risk, and satellite nevi exhibiting negligible risk [6]. Any changes such as variation in color, border irregularity, nodule formation, and asymmetry in the congenital melanocytic nevi should be evaluated histologically for any malignant transformation [7].

Surgical excision is one of the treatment options for large congenital melanocytic nevi, often employing staged excision and subsequent resurfacing via skin grafts, tissue expanders, or flaps for giant lesions [5]. In this report, we document a case involving a male adolescent presenting with a giant congenital nevus accompanied by lipomatosis localized to the right flank.

2. Case History/Examination

A 14‐year‐old male presented with a bathing trunk nevus noted since birth, accompanied by a progressively enlarging soft tissue mass on the right flank over the past 2 years (Figure 1). Physical examination revealed an extensive, asymptomatic, hairy, pigmented patch covering approximately 50% of the skin surface, spanning the back, abdomen, flanks, and thighs. Additionally, multiple pigmented satellite lesions, ranging from 4 to 5 cm in size, were observed scattered across the body and extremities. Notably, a large, irregularly shaped swelling was palpable on the right flank, presenting with soft consistency. The patient had no familial history of similar lesions, and there were no associated congenital anomalies. General physical examination and systemic assessment yielded within normal limits.

FIGURE 1.

A 14‐year‐old boy with giant congenital nevus and progressively enlarging soft tissue mass at the right flank.

3. Investigations and Treatment

Magnetic resonance imaging (MRI) showed a mass within the soft tissue of the right flank, protruding from the skin surface, featuring internal strands, with overall dimensions measuring 167 × 80 × 150 mm. Doppler ultrasound indicated a mass exhibiting fat and vascularity, with no evidence of vascular malformation. Subsequently, the patient underwent local excision of the soft tissue lesion under the care of the general surgery department.

Upon pathological examination, a fibrofatty skin‐covered tissue specimen was received, comprising a large fusiform mass of soft, yellow compact lipomatous tissue, measuring 26 × 17 × 6.5 cm, partially covered by a large ellipse of coarsely granular, finely nodular, dull gray skin, measuring 18.5 × 5 cm in diameter. Histopathological evaluation of the overlying skin revealed an unremarkable epidermis bearing intradermal nests and lobules of oval to spindle cells (Figure 2A), extending deep into the subcutaneous tissue. Sections from the mass exhibited lobules of mature adipose tissue with congested vessels and scattered nests of melanocytes (Figure 2B). Notably, no lipoblasts or atypical cells were identified. Immunohistochemistry staining for HMB45 (a specific marker for melanocytes) (Figure 3A) and S100 (a marker for neural crest origin) (Figure 3B) yielded positive results for both markers.

FIGURE 2.

Microscopic examination showing unremarkable epidermis bearing intradermal nests and lobules of oval to spindle cells (black arrow) (A) extending deep into subcutaneous tissue with lobules of mature adipose tissue with congested vessels and scattered nests of melanocytes (black arrow) (B).

FIGURE 3.

Immunohistochemistry positive for HMB45 (black arrow) (A) and S100 (B) markers (black arrow).

4. Conclusion and Results (Outcome and Follow‐Up)

The patient was discharged with an uneventful postoperative period and is under follow‐up. In this study, we described the association between congenital melanocytic nevus (CMN) and lipomatosis, while also undertaking a comprehensive review of the existing literature pertaining to this uncommon correlation. Given the potential for associated abnormalities, patients diagnosed with CMN necessitate thorough clinical examination to discern any concomitant conditions. The primary objective of treatment endeavors is twofold: to enhance cosmetic appearance and mitigate the risk of malignant transformation. Furthermore, diligent and prolonged follow‐up is imperative to assess both the cosmetic outcomes of interventions and the ongoing risk of malignancy.

5. Discussion

Nevus, derived from the Latin term “knee‐vus” denoting “birthmark” or “mole”, was primarily described by Rokitansky in 1861, in a 14‐year‐old female subject. Congenital melanocytic nevi (CMN) represent pigmented cutaneous lesions originating from nevus cells, specifically nevomelanocytes, located within the epidermal and dermal layers. They manifest in approximately 1 to 2% of neonates, exhibiting a predilection towards females [3, 8]. CMNs are categorized based on their quantity as either solitary or multiple (comprising more than three lesions), and further characterized by size as large (exceeding 20 cm), medium (ranging from 1.5 to 19.9 cm), or small (below 1.5 cm) [9]. Giant CMNs, a rare occurrence, exhibit histopathological diversity, classified as junctional, compound, or intradermal [10]. While predominantly observed on the dorsal trunk, these lesions may also manifest on the head or extremities, characterized by a brown to black verrucous surface, coarse hairs, and irregular margins. Additionally, satellite lesions often emerge in surrounding skin areas. With maturation, giant CMNs undergo mucinous degeneration, resulting in raised, verrucous, hyperkeratotic lesions with increased hairiness. Various anomalies, encompassing limb hypoplasia/hyperplasia, auditory, vascular, and neural developmental aberrations such as spina bifida occulta, have been associated with giant CMNs, presumably stemming from pluripotent neural crest cell abnormalities [4].

The genesis of melanoblasts, Schwann cells, sensory ganglia, bone, fat, muscle, and blood vessels stems from pluripotent neural crest cells, thereby establishing a fundamental association between their development and subsequent aberrations [11, 12]. The central nervous system's melanocortin system intricately regulates food intake and peripheral lipid metabolism, exerting downstream effects on carbohydrate and fat utilization throughout the body via melanocortin neurons and receptors [13]. The autonomic nervous system assumes a pivotal role in modulating energy storage and adiposity, with sympathetic nerve activity within white adipose tissue, mediated by β‐adrenergic receptors, orchestrating alterations in adipocyte metabolism induced by the central nervous melanocortin system [13]. The emergence of lipomatous tissue within giant congenital melanocytic nevi finds explication within these biological phenomena, as lipomas represent a specialized tissue originating from the differentiation of stimulated pluripotent stem cells within the epidermal and dermal layers [14]. Lipomas are benign adipose tissue tumors that appear as masses and are only occasionally symptomatic; the main difference between simple lipoma and lipomatosis is that lipomatosis consists of multiple lipomas in a specific area [15].

A comprehensive review was conducted on cases of giant congenital melanocytic nevus with lipomatosis indexed in PubMed. Inclusion criteria necessitated articles available in English, featuring a diagnosis of giant congenital melanocytic nevus, documented presence of cutaneous lipomatous lesions confirmed through histopathological examination, and normal systemic evaluations encompassing neurological and ophthalmological assessments. Exclusion criteria comprised any concomitant congenital anomalies or syndromes, with histopathological examination demonstrating exclusive lipomatous changes devoid of other pathological findings such as neurofibroma or malignant alterations (Table 1). Our review identified a total of six cases, with a predominance in female patients (5/6). Among these cases, three manifested multiple lipomatous lesions, while two and one case presented with solitary lesions and bilateral flank lesions, respectively. The back emerged as the primary site of occurrence, closely followed by the flank. Surgical excision constituted the primary therapeutic intervention for all identified cases, targeting the removal of lipomatous lesions.

TABLE 1.

Congenital melanocytic nevi associated with lipomatosis reports.

Article	Current age (years)	Lipomatous lesion onset age (years)	Sex	Site	Number of lipomatous lesions
Bhagwat et al. [1]; 2009	12	10	Female	Back and right side of the chest	Multiple
Patel et al. [4]; 2013	34	34	Female	Posterior neck	Multiple
Reddy et al. [2]; 2013	5	4	Female	Left loin	1 lesion
Thakur et al. [16]; 2013	20	N/A	Female	Back and left flank	Multiple
Agarwal et al. [17]; 2019	35	Late childhood	Male	Bilateral flank	2 lesions
Chaoui et al. [18]; 2020	9	N/A	Female	Lateral side of left lumbar area	1 Lesion

Abbreviation: N/A, not available.

The likelihood of malignancy associated with congenital melanocytic nevi depends on several factors, including lesion site, size, and patient age. Given the potential for malignancy, the management of giant CMN necessitates early intervention, typically involving surgical approaches. Such interventions commonly encompass serial excision combined with various reconstructive techniques such as skin grafting, tissue expansion, local rotation flaps, and free tissue transfer. Moreover, advanced laser modalities including carbon dioxide, Er:YAG, and Q‐switched Ruby lasers have recently emerged as viable options for both resurfacing and addressing deep pigmentations associated with giant CMN [14].

Author Contributions

Nabaa Al‐Zubaidi: data curation, project administration, supervision, writing – original draft, writing – review and editing. Sabertehrani Sayna: investigation, methodology, visualization, writing – original draft. Zahra Asadi Kani: data curation, investigation, methodology, visualization, writing – original draft. Mehdi Gheisari: conceptualization, project administration, supervision, writing – original draft, writing – review and editing. Khatere Zahedi: conceptualization, data curation, formal analysis, resources, supervision, validation, writing – original draft, writing – review and editing.

Consent

In compliance with the journal's patient consent policy, the patient's written informed consent was acquired for the publication of this report.

Conflicts of Interest

The authors declare no conflicts of interest.

Al‐Zubaidi N., Sayna S., Kani Z. A., Gheisari M., and Zahedi K., “An Enlarging Mass Superimposed on a Giant Congenital Melanocytic Nevus: A Case Report and Review of Literature,” Clinical Case Reports 13, no. 8 (2025): e70700, 10.1002/ccr3.70700.

Data Availability Statement

The data are available from the corresponding author upon reasonable request.