Introduction

Nodular fasciitis is a benign, rapidly growing soft tissue tumor that, while more commonly seen in adults, can also occur in children. Its sudden appearance and rapid growth can be alarming, often leading to concerns about more serious conditions, such as cancer. However, nodular fasciitis is non-cancerous and typically has an excellent prognosis. This article provides a comprehensive overview of the presentation, diagnosis, and management of pediatric nodular fasciitis to guide healthcare providers and reassure families.

Nodular fasciitis is believed to originate from fibroblasts or myofibroblasts, cells that play a role in wound healing and tissue repair. Although the exact cause of nodular fasciitis is not fully understood, it is thought to result from a reactive process, potentially following minor trauma. In recent years, research has uncovered a specific genetic mutation involving the MYH9-USP6 gene fusion in many cases of nodular fasciitis, suggesting that it may be a clonal neoplastic process rather than a purely reactive one.¹

Nodular fasciitis is relatively rare in children, though it can occur at any age, including infancy. The rarity of this condition in pediatric populations can lead to diagnostic challenges, as clinicians may be unfamiliar with it, especially in young patients.

Clinical Presentation

The hallmark of pediatric nodular fasciitis is the sudden appearance of a rapidly growing mass, typically in the soft tissues just beneath the skin. The key features of this condition include:²

• Location: Nodular fasciitis most commonly appears on the upper extremities (especially the arms), head, neck, or trunk. Less commonly, it can occur on the lower extremities or other areas of the body
• Growth: The mass usually develops over weeks to months. Its rapid growth often prompts concern, as it can double in size within a short time
• Characteristics of the Mass: The mass is typically firm, mobile, and well-circumscribed. It is usually painless, although discomfort can occur if the mass compresses nearby structures. The overlying skin is usually normal, without redness or warmth, which helps differentiate it from infections or inflammatory conditions
• Absence of Systemic Symptoms: Children with nodular fasciitis typically do not experience fever, weight loss, or other systemic symptoms. This absence of systemic involvement is a key feature that distinguishes nodular fasciitis from malignant tumours, such as sarcomas

Differential Diagnosis

Given its rapid growth and firm texture, pediatric nodular fasciitis can be mistaken for other conditions, some of which are more serious. The differential diagnosis includes:

• Rhabdomyosarcoma: A malignant soft tissue tumour common in children, often requiring urgent treatment
• Fibrosarcoma: Another aggressive soft tissue tumour that can present with similar features
• Lymphoma: Particularly when the mass is located in the head and neck region, lymphoma must be considered
• Benign Lesions: These include lipomas, fibromas, and other benign soft tissue masses, which typically grow more slowly

Diagnosis

The diagnosis of pediatric nodular fasciitis involves a combination of clinical evaluation, imaging studies, and histopathological examination.³

• Ultrasound: Often the first imaging modality used, ultrasound can reveal a well-defined, solid mass. The echotexture is typically heterogeneous, with varying degrees of hypoechoic (darker) areas.
• MRI: Magnetic resonance imaging (MRI) is more detailed and can provide information about the size, extent, and characteristics of the lesion. MRI often shows a well-circumscribed, soft tissue mass with variable signal intensity, reflecting its mixed cellular and myxoid components.
• Biopsy: A biopsy is essential to confirm the diagnosis and exclude malignancy. Fine needle aspiration (FNA) or core needle biopsy is usually performed to obtain tissue for histological examination. In some cases, an excisional biopsy, where the entire mass is removed, may be indicated if the diagnosis remains uncertain.
• Histopathology: Under the microscope, nodular fasciitis is characterized by a proliferation of spindle-shaped fibroblasts and myofibroblasts arranged in short, intersecting fascicles. The stroma (background tissue) is often myxoid (gel-like) with areas of increased collagen deposition. Mitoses (cell divisions) are common but appear normal, unlike malignant tumors where abnormal mitotic figures are seen. The "tissue culture" appearance, where the cells look somewhat disorganized, is a distinctive feature.
• Molecular Testing: The identification of the MYH9-USP6 gene fusion can be particularly helpful in confirming the diagnosis, especially when the histological features are ambiguous.

Management

The management of pediatric nodular fasciitis is typically straightforward and conservative, reflecting the benign nature of the condition. ¹

• Observation: Many cases of nodular fasciitis in children can be managed with observation alone. Given the potential for spontaneous regression, a "watch and wait" approach is often appropriate, especially if the mass is not causing symptoms or functional impairment. Regular follow-up visits are important to monitor the lesion's size and ensure that it is not growing or causing complications.
• Surgical Excision: Surgery may be indicated if the mass is causing discomfort, functional problems, or significant cosmetic concerns. Surgical excision is also recommended if there is any uncertainty about the diagnosis. The procedure involves removing the mass with a margin of normal tissue to ensure complete excision. Despite the low recurrence rate, incomplete excision can sometimes lead to regrowth, although this is rare. In cases where recurrence does occur, re-excision is usually curative.
• Post-Surgical Follow-Up: After surgical excision, the follow-up is typically short-term, focusing on wound healing and ensuring that there is no recurrence. Long-term follow-up is generally not necessary, given the benign nature of the condition.

Prognosis

The prognosis for children with nodular fasciitis is excellent. It is a benign condition with no potential for malignant transformation or metastasis. Once the lesion is removed or regresses, it does not typically return, and long-term complications are rare. The overall impact on the child’s health and quality of life is minimal, making nodular fasciitis a condition with a very favourable outcome.

Summary

Pediatric nodular fasciitis, while rare and often alarming due to its rapid growth, is a benign condition that is usually self-limiting. Early and accurate diagnosis, often confirmed through biopsy, is crucial to avoid unnecessary aggressive treatment. Most cases can be managed conservatively, with surgical intervention reserved for symptomatic cases or when there is diagnostic uncertainty. Understanding the presentation, diagnostic process and management options for pediatric nodular fasciitis can help healthcare providers deliver appropriate care and provide reassurance to families facing this unexpected diagnosis.