1. Radiological Findings

Based on the provided ultrasound, CT, and PET/CT images, there is a notable thickening of the left psoas muscle forming a mass-like lesion:

• Ultrasound Findings: Localized coarse echo in the left psoas muscle, showing a “bulging” appearance with unclear boundaries.
• CT Findings: On non-contrast CT, an abnormal soft tissue density is seen within the left psoas muscle, and the surrounding fat planes are partially obscured. No obvious destruction of the vertebral bodies or intervertebral discs is observed. After contrast administration, the lesion shows mild to moderate enhancement.
• PET/CT Findings: Significantly increased 18F-FDG uptake is noted in the left psoas muscle, suggesting a high-metabolic lesion.

The lesion, as shown by the imaging, is confined within the left psoas muscle. No involvement of the lumbar vertebrae, intervertebral discs, or significant renal parenchymal involvement is observed.

2. Potential Diagnoses

Considering the imaging findings and clinical information, the following differential diagnoses can be listed:

1. Psoas Abscess: Common in tuberculosis or bacterial infection, often presents as a local mass with markedly elevated inflammatory markers. However, the patient does not exhibit obvious fever or signs of infection, and tests for tuberculosis are negative.
2. Spontaneous Psoas Hematoma: More common in individuals on anticoagulant therapy or with a bleeding tendency. Imaging characteristics of hematomas may change over time. In this case, the patient has no known history of anticoagulant use or coagulopathy.
3. Malignant Tumors (Lymphoma or Other Soft Tissue Tumors): The psoas muscle is not a common site for lymphoma, but primary muscle involvement (e.g., diffuse large B-cell lymphoma) can occur. Lesions typically appear as soft tissue masses with high metabolic uptake on PET/CT.

Considering the lesion morphology, clinical presentation, and high metabolic activity seen on PET/CT, a malignant lymphoma (especially non-Hodgkin’s lymphoma) should be highly suspected.

3. Final Diagnosis

Pathological biopsy confirmed a primary B-cell lymphoma (non-Hodgkin’s lymphoma, possibly diffuse large B-cell type) in the left psoas muscle. Taking into account the patient’s age, duration of symptoms, clinical labs (moderate elevation in inflammatory markers but no clear evidence of infection), and imaging findings, the final diagnosis is established.

4. Treatment Plan and Rehabilitation

4.1 Treatment Strategy

• Chemotherapy: R-CHOP (Rituximab plus CHOP regimen) is the primary combination chemotherapy, with cycles adjusted according to disease stage and the patient’s general condition.
• Radiotherapy: If the lesion is relatively localized, with a clearly defined extent or residual disease, radiotherapy may be considered to improve local control.
• Other Treatments: Supportive care such as nutritional support, infection prevention, and symptomatic management (pain relief, correction of anemia, etc.) is also essential.

4.2 Rehabilitation and Exercise Prescription

During chemotherapy and/or radiotherapy, patients often experience significant physical exertion, with potential impacts on muscle strength and cardiopulmonary function. To help the patient progressively recover during and after treatment, a step-by-step, individualized exercise prescription is recommended.

• Initial Phase (when overall fitness is relatively low):
  • Types of Exercise: Walking, gentle lower-limb active exercises (e.g., seated leg lifts, standing exercises), simple breathing exercises, etc.
  • Frequency and Duration: 3–4 times per week, 10–15 minutes each session. Gradually increase duration as tolerated.
  • Intensity: Keep the perceived exertion from light to moderate. Avoid excessive fatigue or obvious chest discomfort or shortness of breath.
• Progressive Phase (as strength improves):
  • Types of Exercise: Fast walking, lower-limb strength training (e.g., half squats, resistance band exercises), light to moderate aerobic activities (stationary bike, swimming), etc.
  • Frequency and Duration: 3–5 times per week, gradually increasing to 20–30 minutes per session.
  • Intensity: Aim for a heart rate of about 50%–60% of (170 − age). Adjust based on the patient’s tolerance.
• Consolidation & Maintenance Phase:
  • Types of Exercise: Moderate-intensity aerobic activities (such as brisk walking, slow jogging, elliptical, swimming), possibly combined with resistance training.
  • Frequency and Duration: 3–5 times per week, 30–45 minutes each session. Coordinate with chemotherapy cycles as needed.
  • Set short-term (every 2–4 weeks) and long-term goals. Evaluate patient tolerance, potential bone health concerns, and cardiopulmonary status. Communicate and adjust accordingly.

Throughout the rehabilitation process, closely monitor the patient for signs of excessive fatigue, worsened pain, or any other discomfort. If abnormalities occur, promptly consult with the attending physician and adjust the exercise plan. If there is any concern regarding bone fragility or anemia caused by chemotherapy, choose appropriate weight-bearing and resistance levels under professional guidance.

5. Disclaimer

This report provides a reference analysis based on the current information provided by the patient and does not replace an in-person consultation or professional medical advice. Specific treatment and rehabilitation plans should be determined according to the patient’s actual condition, treatment response, and comprehensive evaluation by professional healthcare teams.