Imaging Findings

A large soft tissue mass is visible in the patient’s right thigh. X-ray imaging reveals no obvious bone destruction or fracture signs; the femur appears generally normal, with no significant periosteal reaction or bone erosion.
On MRI cross-sectional and sagittal views, the lesion is located within the subcutaneous soft tissue of the right thigh, with a relatively clear boundary to the surrounding muscle layers (especially the vastus lateralis), but closely adherent to the muscle fascia in some areas. Inflammatory changes are noted around the lesion boundary. The lesion signal is primarily fluid-like, and some regions display a fluid-gas level. The overall appearance suggests a cystic or purulent fluid lesion.

Potential Diagnoses

• Subcutaneous abscess (or infectious cystic lesion):
  A longstanding hematoma after trauma may persist and become secondarily infected. The presence of a fluid-gas level on MRI, along with adjacent soft tissue inflammatory changes, is consistent with an abscess.
• Benign subcutaneous tumor (e.g., lipoma):
  Lipomas typically exhibit fat signals on imaging. However, they usually do not present with fluid-gas levels and are less likely to show signs of infection.
• Other infections or parasitic cysts (e.g., echinococcosis or sparganosis):
  Although parasitic cysts have been reported in muscle or subcutaneous tissues, the epidemiological incidence is relatively low, and they often exhibit additional clinical or imaging features.
• Malignant tumors (e.g., liposarcoma, rhabdomyosarcoma):
  Malignant soft tissue lesions often show heterogeneous signals, indistinct boundaries, and may cause destruction or infiltration of surrounding structures. While central necrosis in a tumor could mimic an infectious lesion, in this case, the infection indicators and fluid-gas level suggest an abscess.

Considering the lesion’s signal characteristics, the presence of a fluid-gas level, surrounding soft tissue reactions, and clinical findings (fever, elevated white blood cells and CRP, and bacterial culture results), an infectious lesion (abscess) is the most likely diagnosis.

Final Diagnosis

Given the patient’s advanced age, history of trauma leading to a chronic hematoma, persistently palpable mass in the right thigh, and the identification of Staphylococcus aureus infection after surgical drainage, combined with MRI findings of a fluid-gas level in a subcutaneous cystic lesion and local inflammatory signs, the most probable diagnosis is “Right thigh subcutaneous abscess (chronic hematoma with secondary infection)”.

Treatment Plan and Rehabilitation Program

1. Surgical Treatment:
· For a confirmed abscess, surgical incision and drainage should be performed. Since the patient’s culture has identified Staphylococcus aureus, targeted antibiotic therapy based on drug sensitivity results is recommended.
· If a residual cavity or lesion remains, further management may involve catheter drainage and regular irrigation.

2. Antibiotic and Supportive Therapy:
· Choose targeted antibiotics according to culture and drug sensitivity results, and correct electrolyte imbalances as well as nutritional deficiencies.
· Given the patient’s advanced age, liver and kidney function along with overall tolerance must be considered. Adjust the dosing regimen as needed.

3. Rehabilitation and Exercise Prescription:
· Early Postoperative Stage: Focus on wound healing and controlling the infection. Keep the affected limb appropriately immobilized and elevated to promote return of blood and lymph flow. Perform passive joint movements and slight active exercises in bed to maintain basic joint mobility and prevent stiffness.
· Once Inflammation is Generally Controlled: Gradually increase weight-bearing and activity. Begin mild active flexion and extension exercises. Light resistance training with elastic bands may be introduced.
· Later Recovery Stage: As the patient’s overall condition improves, gradually increase the intensity and duration of training. It is recommended to follow the FITT-VP principle (Frequency, Intensity, Time, Type, Volume, and Progression):

• Frequency: Conduct lower limb function training 3–4 times a week, adjusting according to the patient’s tolerance.
• Intensity: Start with mild to moderate levels, aiming for a perceived exertion rating (RPE) of about 10–12 on a 20-point scale, and gradually increase.
• Time: Begin with 15–20 minutes per session, progressively extending to 30 minutes or more, depending on physical capacity and recovery.
• Type: Include range-of-motion exercises, wall-sits, simple weight-bearing exercises, and—once the infection is fully controlled—low-impact aerobic workouts with a stationary bike.
• Progression and Volume: As safety and comfort allow, incrementally increase training time or resistance. Reassess and fine-tune every week or two.

Disclaimer

This report is based on imaging and clinical information for reference only and cannot replace face-to-face consultation or professional medical advice. Please combine the patient’s actual condition with professional medical consultation for a definitive treatment plan.