Introduction

Imagine discovering a rapidly growing lump under your skin, a scenario that often raises concerns about cancer and the possibility of aggressive treatments. Nodular fasciitis (NF) often evokes such concerns due to its fast growth and tumour-like appearance. However, despite its alarming presentation, NF is a benign condition, distinct from malignant sarcomas.

NF is a non-cancerous soft tissue tumour in fascia, a layer of soft tissue that covers and separates different organs, muscles, blood vessels and nerves. It can occur in soft tissues such as deep fascia, in the skin (dermis), near blood vessels, between muscles and inside muscles.¹

This soft tissue tumour, which can affect both adults and children, varies in its manifestation and treatment between these two groups. Understanding these differences is crucial for accurate diagnosis and management, ensuring that patients receive appropriate care tailored to them. This article will look at the differences in pathology, treatment and diagnosis between adults and children experiencing NF. 

Prevalence 

NF is relatively uncommon, and reports show prevalence between 7% to 15% of the population.^2,3,4 Young adults are the most affected population, and NF in adults is most commonly found in the forearms, upper arms and back and chest wall, and occasionally the hands and face.^5,6 Only half of all adult cases report experiencing pain, discomfort, or redness. Associated pain is often correlated to pressure on the surrounding nerves.^6,7

In contrast, only around 10% of all reported NF cases occur in children. Some studies suggest a slight predominance in people assigned male at birth (AMAB).⁸ Pediatric cases more commonly involve pain, tenderness, or redness.⁹

Pathology 

NF typically grows rapidly over one to two weeks and generally remains under 3 cm in size (or just over one inch). While it may be tender to the touch, it is not usually highly painful, a key feature distinguishing it from malignant tumours like sarcomas.^1,7,8 

In adults, NF is most frequently associated with the upper body, especially the upper extremities.⁶ The tumour is thought to be a reactive lesion, often associated with minor trauma or inflammation.¹⁰

In children, NF appears to be mostly present around the head, face, neck, and ears, areas more prone to injury and trauma during play.^3,4,8,9,10 Similar to adults, the size of NF will not surpass 3 cm in size, but it may be more prone to redness or discomfort.¹¹ Pediatric NF poses a greater diagnostic challenge, as its rapid growth and high cellularity may mimic aggressive tumours such as rhabdomyosarcoma.^10,7

A significant number of both paediatric and adult cases of NF have been linked with a genetic fusion of genes USP6 and MYH9 found in cells examined after biopsy. The USP6 and MYH9 genes have also been found overexpressed and rearranged in mRNA.¹² Interestingly, USP6 overexpression has also been found in other benign tumours, suggesting a broader role in reactive soft tissue lesions.¹² 

Diagnosis 

Due to its rapid growth and cellular appearance, NF is frequently misdiagnosed as malignant tumours like sarcoma, myositis ossificans, or even breast cancer. Accurate diagnosis is essential to avoid unnecessary and invasive interventions.^7,13,14 

Clinical evaluation typically involves imaging (ultrasound or MRI), followed by a biopsy, which confirms the benign nature of the tumour.^1,8,15,16 In ambiguous cases, molecular testing may be conducted to detect the USP6-MYH9 gene fusion, helping to rule out malignancy.^16,17 Children are often subjected to more extensive diagnostic workups, due to greater concern over malignancy.^9,18 

In the case of NF, diagnosis can play a bigger role than we might think. Its close resemblance to sarcomas, characterised by rapid growth and cellular appearance, similar to NF, can lead to unnecessary extensive surgical procedures, aggressive treatment, and psychological and financial distress for the patients and their families. Hence, examination of the tissue and cells under a microscope and immunohistochemical staining, checking for antibodies and disease-specific markers, are critical for diagnosis.¹⁷

Treatment 

NF is a benign growth and some cases may not require treatment at all. The lumps have been observed to go away on their own within three months. Although a spontaneous, automatic breakdown of the NF is possible, it can be difficult waiting for it to resolve itself due to pain, discomfort, and functional impairment due to pressure on surrounding nerves, therefore, surgical or non-surgical removal might still be recommended by specialists. 

In adults, recurrence of NF is rare following complete surgical removal. However, one study found that when NF occurs on the face in adults and is treated using a carbon dioxide (CO₂) laser, recurrence rates are significantly higher. Specifically, NF on the face reoccurred in approximately 78% of initially treated patients, likely due to the challenges of achieving full removal in such a sensitive and anatomically complex area, where minimising scarring is also a concern.¹⁹ 

As a result, some clinicians advocate for non-surgical approaches, such as corticosteroid injections and CO₂ laser treatment, to reduce the risk of scarring. The same study also identified a genetic mutation present in biopsy samples from recurring cases, which may contribute to the high recurrence rate.^19,20

In children, surgery is more often performed promptly due to concern over malignancy. Nevertheless, recurrence after complete excision is rare in the pediatric population as well.^9,11,18

Prognosis

The prognosis for NF is excellent in both adults and children. As a benign lesion, NF has a low impact on long-term survival and is rarely associated with other health conditions. Although recurrence is uncommon, close monitoring post-treatment is advisable, especially for facial lesions or in cases of incomplete excision.²¹

Summary 

Nodular fasciitis, despite its benign nature, poses significant diagnostic and therapeutic challenges, particularly due to its rapid growth and resemblance to malignant tumours.

In adults, NF is most often found on the upper extremities and back, with a generally straightforward diagnostic and treatment approach. In children, it more commonly affects the head and neck, often requiring more extensive testing due to concerns about malignancy.

Recognising the subtle yet significant differences in presentation and management between adults and children is essential for healthcare providers, ensuring that patients receive timely, accurate, and effective care.