A 17-Year-Old Male Adolescent With a Giant Isolated Scalp Neurofibroma Associated With a Calvarial Defect: A Case Report

Introduction

Neurofibromas are benign tumors originating from the peripheral nerve sheath and typically contain heterogeneous structures composed of Schwann cells, perineural cells, and fibroblasts [1,2]. Clinically, they can present as solitary or multiple lesions. The multiple form is usually associated with neurofibromatosis type 1 (NF1); this syndrome is due to the loss of the tumor-suppressing neurofibromin protein as a result of a mutation in the NF1 gene [3,4].

The prevalence of NF1 in the general population ranges from 1 in 2500 to 1 in 4000 [5]. Patients may present with café-au-lait spots, axillary lentigines, Lisch nodules, bone dysplasias, and multiple cutaneous neurofibromas [4,6]. However, isolated neurofibromas developing without NF1 also exist; these are typically located in the head and neck, trunk, or extremities [7].

Neurofibromas located in the scalp and cranial region are extremely rare, with only a few cases reported in the literature [8,9]. These lesions usually present as slowly growing, ill-defined, soft tissue masses under the scalp. Rarely, they may be accompanied by thinning or defects in the calvarial bone [10,11].

Careful investigation of bone involvement, determination of dural relationships, and planning of reconstruction are important in the preoperative assessment. Histopathologically, neurofibromas are characterized by S-100 protein and SRY-related HMG-box 10 (SOX-10) positivity, CD34 stromal network, low Ki-67 proliferation index, and the presence of axons entrapped by neurofilament [1,12]. The risk of recurrence is generally low but may be increased, particularly in diffuse and plexiform variants.

This report aims to describe the clinical, radiological, surgical, and histopathological features of a rare isolated giant scalp neurofibroma without NF1.

Case Report

A 17-year-old male patient presented to our clinic with a gradually enlarging swelling in the left occipital region. According to the patient and his family, the mass had first been noticed at approximately 7 years of age and had progressively increased in size over the past 10 years. The lesion was painless and was not associated with any history of trauma, infection, or congenital abnormality.

On physical examination, a soft, mobile, subcutaneous mass measuring approximately 85×67 mm was identified in the occipital region. The lesion was covered by intact, normally colored skin without ulceration or vascular changes. There were no signs suggestive of NF1, such as café-au-lait macules, axillary or inguinal freckling, cutaneous neurofibromas, or skeletal abnormalities.

Preoperative computed tomography (CT) demonstrated a focal calvarial defect measuring approximately 1 cm in diameter in the underlying occipital bone (Figure 1). Magnetic resonance imaging (MRI) revealed a well-circumscribed, subcutaneous mass without intracranial extension or dural involvement (Figure 2).

The patient underwent surgical excision under general anesthesia. Through an elliptical skin incision, the lesion was carefully dissected from the surrounding tissues and removed in total. Intraoperatively, the mass was found to be confined to the subcutaneous layer, without dural adherence. An intraoperative gross photograph demonstrates the irregular, lobulated, soft tissue mass following complete surgical excision (Figure 3). The small calvarial defect did not require reconstruction and was managed conservatively. The wound was closed primarily, and an acceptable cosmetic result was achieved.

Histopathological examination demonstrated spindle-shaped cells with elongated, wavy nuclei embedded in a collagenous and partially myxoid stroma. Immunohistochemical analysis revealed tumor cell positivity for S-100 and SOX10, along with a CD34-rich stromal network. The Ki-67 proliferation index was below 1%, consistent with a benign neurofibroma (Figures 4–8).

Further evaluation, including dermatological and ophthalmological examinations, did not reveal any findings fulfilling the National Institutes of Health diagnostic criteria for NF1. The postoperative course was uneventful, and no recurrence was observed during 1-year follow-up. Postoperative CT confirmed complete excision, without residual lesion (Figure 9).

Discussion

This case highlights the rare occurrence of a giant isolated scalp neurofibroma without NF1 and emphasizes the importance of thorough diagnostic evaluation and surgical planning.

Scalp neurofibromas are exceedingly rare lesions, particularly when they occur in the absence of NF1. Most published cases describe solitary or diffuse masses that enlarge gradually over several years, often remaining asymptomatic aside from cosmetic concerns [9,10].

Similar to previously reported cases, our patient presented with a large, slowly expanding occipital mass that developed over a decade, ultimately reaching 85×67 mm in size and causing focal calvarial erosion. Nehete et al reported a diffuse scalp neurofibroma with a calvarial defect in a young woman, emphasizing that bony involvement should raise suspicion for long-standing pressure effects and may influence surgical planning [9]. Likewise, Kumar et al described a giant solitary neurofibroma measuring 9×8 cm associated with bone thinning, further supporting the association between large scalp lesions and remodeling of adjacent bone structures [11]. Our case is consistent with this pattern, reinforcing that chronically enlarging scalp neurofibromas can lead to calvarial defects even in the absence of NF1.

Histopathological evaluation remains critical for differentiating neurofibromas from other peripheral nerve sheath tumors, including schwannoma and malignant peripheral nerve sheath tumors [2]. Neurofibromas typically exhibit a myxoid stroma with spindle cells, scattered S-100 and SOX-10 positivity, and a CD34-rich stromal network, whereas schwannomas demonstrate much more diffuse S-100 expression [12]. The low Ki-67 proliferation index (< 1%) in our case further supports a benign biological behavior [1]. These findings align with current literature describing the classical immunoprofile of neurofibromas and highlight the importance of immunohistochemistry in distinguishing benign lesions from more aggressive or malignant variants.

Surgical excision is considered the gold standard for treatment, with the objective of complete resection whenever feasible [11]. However, diffuse or plexiform neurofibromas can present challenges due to poorly defined margins and infiltrative growth patterns. Although solitary neurofibromas carry a very low risk of recurrence, plexiform variants are associated with higher recurrence rates and an established risk of malignant transformation [10]. Permana et al demonstrated recurrence in a plexiform scalp neurofibroma in a patient with NF1, while other reports have documented malignant transformation into malignant peripheral nerve sheath tumor in neglected or long-standing lesions [13,14]. In contrast, our patient demonstrated no plexiform components and met none of the NIH diagnostic criteria for NF1, indicating a very low likelihood of malignant transformation. Nonetheless, long-term follow-up is recommended, especially in lesions of considerable size or those associated with calvarial involvement.

The absence of congenital onset, infiltrative growth pattern, and plexiform architecture further supports the diagnosis of a solitary localized neurofibroma rather than a plexiform variant.

Calvarial defects associated with scalp neurofibromas are uncommon but clinically relevant. These defects are believed to result from chronic pressure exerted by the expanding mass rather than direct tumor invasion. While small defects may be managed conservatively or closed primarily, larger defects may require cranioplasty using titanium mesh or other reconstructive materials, depending on cosmetic considerations and patient age [9]. In our case, the bone defect was limited to approximately 1 cm, allowing for primary closure without the need for reconstruction, and an excellent cosmetic result was achieved.

Overall, this case contributes to the growing body of literature describing isolated, large scalp neurofibromas without NF1 features, a rare clinical entity. The prolonged course, associated calvarial defect, and classic immunophenotype make this case a valuable addition to existing reports. Our findings underscore the importance of thorough preoperative assessment, including evaluation of bone and dural relationships to ensure safe resection and optimal outcomes.

Conclusions

This case highlights a rare presentation of a large isolated scalp neurofibroma occurring without any clinical or radiological evidence of NF1. Despite its benign nature, the long-standing lesion resulted in calvarial remodeling, emphasizing the importance of detailed preoperative imaging in lesions affecting the scalp and cranial vault. Complete surgical excision provided both diagnostic confirmation and excellent cosmetic and clinical outcomes.

While the risk of malignant transformation is minimal in solitary neurofibromas, especially in the absence of NF1, regular follow-up remains advisable, particularly for large lesions or those associated with bony changes. This report reinforces that scalp neurofibromas, although uncommon, should be included in the differential diagnosis of slow-growing scalp masses, and that timely surgical intervention can prevent progression and improve patient quality of life.

By presenting this case, we aim to expand current understanding of isolated scalp neurofibromas and provide guidance for clinicians in the evaluation, surgical management, and follow-up of similar lesions.