The objective of this study is to explore the role of ultrasonography (non-invasive imaging device) in the diagnosis of subcutaneous nodules (mass/bumb underneath the skin).

Patients who presented with subcutaneous nodules and was indicated for diagnostic skin biopsies were recruited. Prior to skin biopsies (not part of the study's intervention), ultrasonography(intervention) was used to examine the characteristics of the nodules. The ultrasonographic findings are then compared to the pathological results to explore the role of ultrasonography in differentiating each disease or group of diseases that presented with skin nodules.

Panniculitis refers to a group of conditions involving inflammation of the fat cells in the subcutaneous tissue. It can result from various causes, such as inflammation, infection, vasculitis (inflammation of blood vessels), or lymphoproliferative disorders (abnormal lymphocyte proliferation). In general, it is challenging to determine the cause of subcutaneous tissue inflammation based solely on skin manifestations, as patients often present with similar symptoms, such as subcutaneous lumps, tenderness, and redness, usually found in the lower limbs. Therefore, diagnosis often requires a comprehensive patient history taking, physical examinations, and sometimes biopsy for histopathological examination to confirm the diagnosis. Occasionally, additional tests, including immunohistochemistry, cultures, or polymerase chain reaction (PCR), may be necessary for greater diagnostic accuracy.

Since 1997, Ackerman has proposed diagnostic guidelines for panniculitis based on histopathological findings, initially categorizing it according to the site of inflammation into septal panniculitis and lobular panniculitis. Further classification considers whether vasculitis is present. However, even with physical examination and histopathological analysis, accurately classifying panniculitis remains challenging. In 2007, Requena and colleagues highlighted limitations in biopsy, such as the selection of lesions with differing characteristics or lesions at different stages, resulting in varying histopathological features. Moreover, the depth or insufficient amount of tissue collected for biopsy may reduce diagnostic accuracy.

Since 1979, medical advancements have led to the increased use of ultrasound in dermatological diagnosis. Low-frequency ultrasound machines (2 MHz) were initially used to examine skin lesions, such as skin inflammation or subcutaneous nodules. In 1983, Miyauchi and colleagues began using higher-frequency ultrasound (10 MHz) to study ultrasound characteristics compared to histopathological results in patients presenting with subcutaneous or dermal nodules. Over time, the use of higher-frequency ultrasound became more common, as it provides better detail and convenience, being a simple, safe, and cost-effective procedure.

For panniculitis, research has shown that ultrasound can assist in diagnosis. In 2020, Romani and colleagues studied the correlation between ultrasound findings and histopathology in 62 cases of panniculitis. Septal panniculitis typically shows thickening of the septa with hypoechoic areas resembling a jigsaw pattern, difficult to compress, increased blood flow, and possible clotting in veins. Lobular panniculitis shows hyperechoic fat with irregular borders, without septal thickening or increased vascularity, and may show fat necrosis or extension into muscles and adjacent tissues. However, further research is needed for clear differentiation between types of panniculitis based on ultrasound features.

Subsequent studies have used ultrasound to describe various forms of panniculitis, including those caused by gout, erythema nodosum, lupus erythematosus, and subcutaneous T-cell lymphoma, among others.

In conclusion, diagnosing panniculitis in patients with subcutaneous nodules remains challenging and relies on a combination of physical examination, patient history, histopathology, and sometimes additional tests like immunohistochemistry, cultures, or PCR. These diagnostic procedures can lead to unnecessary testing and delays in diagnosis. Ultrasound data can assist in selecting appropriate laboratory tests, facilitate diagnosis and treatment monitoring, and aid in selecting biopsy sites. However, there is no comprehensive collection of ultrasound data for different conditions, which is why this study was conducted to gather this information and explore the correlation between ultrasound findings and histopathological features for more accurate diagnosis.

Inclusion Criteria:

• Patients aged 18 years and older who presented with subcutaneous nodules
• Indicated for pathological examination for disease diagnosis.
• Patients with subcutaneous nodules located in areas where a tissue sample can be taken down to the fat layer.
• Patients who agree to participate in the project by signing the consent form.

Exclusion Criteria:

• Presence of inflammation or other tumors that can mimic panniculitis, such as painful lipomas, cellulitis, and leg interstitial edema.
• Patients with diseases that significantly alter the structure of the skin or subcutaneous tissue, such as scleroderma or severe edema.
• A history of previous treatments in the area of the subcutaneous mass (e.g., surgery, radiation therapy, or high-dose steroid treatment) that may interfere with ultrasound results.
• Patients with lesions on the head or mucous membranes of the body.
• Pregnant or breastfeeding patients.
• Presence of wounds or open sores in the area to be examined with ultrasound.
• A history of coagulopathy (blood clotting disorders).
• Patients with metal implants in the area of interest that may interfere with ultrasound imaging.
• Participants who refuse or withdraw from the study.