Diagnosis of nodular fasciitis

Finding a fast-growing lump that appears out of nowhere on your arm or leg can be highly alarming and raises an immediate fear of cancer. However, before jumping to such conclusions, we must consider the potential that it could be a benign (non-cancerous) condition called nodular fasciitis. Unfortunately, this type of tumor can commonly camouflage as a variety of other tumours, which can lead to healthcare professionals misdiagnosing nodular fasciitis for much more serious conditions, causing unnecessary anxiety to the patient. 

What is nodular fasciitis?

Nodular fasciitis is a fast growing non-cancerous (benign) tumor that typically grows within the fascia (connective tissues supporting body structures).² The condition is commonly seen in younger age groups, particularly between the ages of 20-50 and has several names that are used by healthcare providers including:^1,4

• Infiltrative fasciitis 
• Pseudosarcomatous fasciitis 
• Pseudosarcomatous fibromatosis 

Nodular fasciitis is most commonly located on the upper parts of the body such as the forearm, and less commonly seen within regions of the head and neck. Nodular fasciitis can be characterized into 3 subtypes: subcutaneous (beneath the skin), intramuscular (in muscles) and fascial (in fascia).⁴

What causes nodular fasciitis?

The cause of Nodular fasciitis is mostly unknown, but it has been characterized by a random proliferation of myofibroblasts which could potentially be triggered upon injury to cause an inflammatory response.¹ Alternatively, researchers are investigating a potential genetic influence from chromosomal gene rearrangement.⁶

Misdiagnosis of nodular fasciitis

Nodular fasciitis can often present as more serious conditions and can easily become confused with malignant forms of tumors such as sarcomas. 2 out of 11 cases of nodular fasciitis have been misdiagnosed as sarcoma, leading to their alternative name of pseudosarcomas.^2,3 This misdiagnosis occurs due to their similar diagnostic characteristics to nodular fasciitis, such as rapid growth and similar imagery (CT and MRI) of poorly defined borders.⁷ Distinguishing nodular fasciitis from other conditions, especially confirming if they are benign or malignant is of the utmost importance so patients receive the right treatment.

Methods for differential diagnosis of nodular fasciitis

There are a variety of tumours similar to Nodular fasciitis including but not limited to:^2,7

• Desmoid tumours 
• Schwannomas 
• Myositis ossificans 
• Lipomas
• Dupuytren’s disease 
• Neurofibromatosis 
• Myxomas 
• Fibrous histiocytoma 
• Fibrosarcomas 
• Myxofibrosarcoma 
• Fibromatosis 

Differential diagnosis of nodular fasciitis involves distinguishing this condition from other mimicking tumours that are benign, or more importantly, malignant. To diagnose a patient with nodular fasciitis, a combination of the patient’s medical history, clinical presentation, imaging (CT, MRI, ultrasound), and histopathology of a biopsy are considered.⁶ Often a biopsy is essential for diagnosis by a pathologist. Histology plays an important role in differential diagnosis, for instance, nodular fasciitis can be distinguished through the use of cytological atypia in spindle-cell sarcomas.¹

Nodular fasciitis diagnosis

• Clinical features:^2,4
  • Rapid growth of the mass that tends to feel relatively solid 
  • Common locations in upper extremities, such as the forearm, however can also be seen in the torso, head, back, neck and lower limbs 
  • Lump that is usually smaller than 1.5 inches but can grow up to 5 inches 
  • On rare occasions it can lead to loss of sensation, tingling and paralysis as a result of the tumour pressing against peripheral nerves 
• Histopathology:^4,5
  • Large amount of cells with plump fibroblasts particularly arranged in bundles which can be similar to sarcomas, provide an indicator for the age of the tumour
  • Well defined mass within subcutaneous adipose (fat storage) tissues 
  • Large amount of red blood cell infiltration and inflammation 
•  Imagery:⁴
  • Well-defined shape on MRI, however appearance can vary 

Differential diagnosis for Benign tumours

Myositis ossificans

• Clinical presentation:⁸
  • Presented more in males than females 
  •  Usually occurs within muscles in extremities (limbs) 
  • Often occurs following trauma with gradual development over time, commonly seen within sports injuries⁸

• Histopathology:⁸
  • Proliferation of fibroblasts, myofibroblasts with some bone formation occurring 
  • High mitotic activity stage which looks similar to sarcomas in early stages, but develops further 
• Imagery:^8,9
  • CT scans can identify ossification patterns (connective tissue converting into new bone tissue) in later stages 
  • MRI is commonly used to identify the mass with oedema and later more mature peripheral ossification 

Lipoma

• Clinical presentation:¹⁰
  • Slow growing 
  • Can appear anywhere, but more common on neck, head, shoulders and back 
  • Typically seen in middle-aged and elderly adults with no differences between sex 
  • Usually there are no symptoms or pain unless localised on top of a nerve or blood vessels 
  • Relatively soft and mobile
  • Sometimes associated with certain disorders that can be hereditary 
  • May potentially be a result of trauma 
• Histopathology:¹⁰ - Composed of mature adipocytes (fat storage cells)¹⁰
• Imagery:^{10, 11}
  • Lesion similar to subcutaneous fat on CT scan¹¹
  • MRI shows homogenous tissue with well-defined margins and similar signal intensity as adipose tissue
  •  Lipoma (benign lump formed by overgrowth of fat cells) should be deeper than other fatty tissue

Desmoid tumours

• Clinical presentation:^{12, 13}
  • Relatively rare, seen in 3-4 cases per 1 million 
  • Can grow in any part of the body, but common in head, neck, pelvis, rectus abdominis muscle and extremities 
  • High risk of local recurrence 
  • Typically seen in younger age groups 
  • High mimicry of cancer although metastasis cannot occur 
• Histopathology:¹²
  • Spindle cell proliferating looks like myofibroblasts 
  • High content of myxoid stroma 
  • Positive for B-catenin and vimentin, but negative for desmin 
• Imagery:¹²
  • MRI and CT used to see organ infiltration 

Differential diagnosis fom Malignant tumors

Sarcomas

• Clinical presentation:^14,15,16
  • Rare malignant tumor, with majority of sarcomas being soft tissue 
  • Can occur anywhere in the body within supportive tissues 
  •  Large, fast-growing lump that can become painful 
  •  Affects any age group, however certain sarcomas may be more common than others in certain age groups
  • May be potentially linked to an inherited risk factor 
• Histopathology:¹⁷
  • Different sarcomas have different characteristics 
  • Attempt to grade tumour for prognosis 
  • Immunohistochemistry can be used to aid in diagnosis 
• Imagery :^14,17
  • X-rays can be used to look at soft tissues 
  • CT scans provide cross sections of the soft tissues throughout the body to assess metastasis 

Metastatic squamous cell carcinomas e.g to the neck

• Clinical presentation:^{18, 19, 21}
  • Relatively uncommon for metastasis to occur 
  • Physical presentation is highly variable from a lump, a flat/raised sore or even just a red patch 
  • Commonly metastasis occurs from skin to neck lymph nodes 
  • Can present as a lump on the neck or in the back of the throat 
• Histopathology:^19,20
  • Pathologist will look for characterized features such as degree of differentiation and depth of more than 2mm 
  •  Immunohistochemistry will help identify what kind of cancer it is 
• Imaging in diagnosis:¹⁸
  • CT and MRI scans can be used to assess extent of spread of the carcinoma, including the lymph nodes to determine prognosis 

Treatment and management of nodular fasciitis

Nodular fasciitis is benign, however, depending on the location, surgical excision may be required.² Recurrence of the lesion is rare, as it has been observed in only 1-2 % of patients.⁴

Summary

Despite being benign, nodular fasciitis can easily be misdiagnosed due to its similarities to both benign and malignant tumors. Therefore, careful consideration must be taken by healthcare providers when conducting diagnosis of a tumour. However, there are promising advances of molecular markers for the gene rearrangement that have been observed in nodular fasciitis, which could provide a more precise, efficient, and less invasive differential diagnosis.⁶ Additionally, improving imaging techniques and histopathological methods could aid in the accuracy of nodular fasciitis diagnosis. These advancements not only improve the detection of nodular fasciitis but also aid in early identification of malignant tumours, facilitating timely treatment and potentially reducing mortality rates. Overall, refining diagnostic techniques and understanding of nodular fasciitis will equip healthcare providers with augmented accurate diagnosis, improving patient outcomes and alleviating anxiety from misdiagnosis.