Subcutaneous dirofilariasis

Subcutaneous dirofilariasis is a parasitic infection caused by the filarial worm Dirofilaria repens. Ultrasound imaging findings for subcutaneous dirofilariasis may include:

1. Hypoechoic (dark) or anechoic (black) linear or serpentine structures within the subcutaneous tissue, representing the presence of the parasitic worms or their larval tracks.

2. Surrounding inflammation and edema due to the body's immune response to the infection.

Color Doppler shows normal vascularity. 

Case Study: Subcutaneous Dirofilariasis Lesion on Ultrasound

Case study:

Patient Information:

- Age: 45 years

- Sex: Female

- Clinical Presentation: The patient presented with a painful, erythematous subcutaneous lesion on her abdomen that had been gradually increasing in size over the past two weeks. There was no history of recent travel or exposure to animals.

Ultrasound Findings:

- Ultrasound examination of the left forearm revealed a well-defined, hypoechoic (dark) subcutaneous lesion measuring approximately 1.5 cm in diameter.

- Within the lesion, there was a small cystic area with internal echoes, resembling a serpentine or linear pattern.

- Surrounding the lesion, there was evidence of mild inflammation with hypoechoic edema.

- No vascularity was noted within the lesion on color Doppler imaging.

Diagnosis:

Based on the characteristic ultrasound findings of a small cystic area with internal echoes and a serpentine pattern within the subcutaneous tissue, the diagnosis of subcutaneous dirofilariasis was seen. 

Conclusion:

Ultrasound imaging played a crucial role in diagnosing subcutaneous dirofilariasis by revealing the characteristic features of the parasitic infection. Timely surgical intervention and appropriate management led to the successful removal of the worm and a favorable outcome for the patient.

Differential diagnoses to consider for subcutaneous dirofilariasis on ultrasound include:

1. Subcutaneous Epidermoid Cyst: Epidermoid cysts typically appear as well-defined, oval-shaped, hypoechoic lesions with a hyperechoic wall, containing keratin debris. They lack the linear or serpentine appearance seen in dirofilariasis.

A punctum is seen on examining the epidermoid cyst. This is also called a sebaceous cyst. 

2. Abscess: Abscesses may appear as fluid-filled, hypoechoic masses with surrounding inflammation, but they lack the characteristic linear or serpentine structures seen in dirofilariasis.

Prognosis and management of subcutaneous dirofilariasis typically involve:

1. Surgical Removal: The primary treatment is surgical excision of the worm or larval tracks, along with any associated inflammation or abscesses.

2. Antibiotics: Antibiotics may be prescribed to prevent or treat secondary bacterial infections.

3. Follow-up: Patients are usually monitored for any signs of recurrence or complications.

The prognosis for subcutaneous dirofilariasis is generally good with prompt diagnosis and appropriate treatment. However, the exact outcome can vary depending on the extent of infection, the presence of secondary complications, and the patient's overall health.