Medical Imaging and Clinical Analysis Report

1. Imaging Findings

Based on the provided X-ray, MRI, and CT images of the lower limb, a significant mass is observed in the anterior soft tissue area of the right thigh. The main characteristics are as follows:

• On the X-ray: A localized protrusion-like change on the bone surface is visible, with some lesions appearing as sclerotic densities and relatively clear boundaries. No obvious sign of intramedullary involvement is noted.
• On the MRI axial (T1 and T2-weighted) images: The main part of the lesion mostly shows low-to-medium signals, with some areas possibly showing high signal intensity, suggesting soft tissue or a small amount of edema. At the junction with the bone cortex, a locally thickened cortical layer or a thin boundary (“string sign”) can be seen.
• On the CT axial images: The lesion mainly presents as high-density ossification, with no significant expansion of the surrounding soft tissue component. No evident sign of medullary cavity invasion is observed so far.

2. Potential Diagnoses

Combined with the patient's medical history (62-year-old female, 6 months of painless swelling, no obvious history of trauma or weight loss) and the imaging characteristics, the following diagnoses are considered:

1. Parosteal Osteosarcoma:
   This is the most common type of surface osteosarcoma, frequently occurring in adults, often found on the distal femur (commonly posterior, but the anterior side can also be involved). The tumor often presents with an exophytic growth pattern and shows dense or lobulated ossification. A “string sign” often separates the normal bone cortex from the tumor. The patient's age and imaging findings are consistent with this condition.
2. Periosteal Osteosarcoma:
   More often occurs in younger patients (around the second decade of life) and can be of moderate to high malignancy. It commonly shows marked periosteal reaction with a cartilaginous matrix and occurs in mid-diaphyseal regions. The presentation here does not fully match, but it remains a differential diagnosis.
3. High-grade Surface Osteosarcoma:
   On imaging, there would typically be more bone destruction, a prominent periosteal reaction, and more extensive soft tissue infiltration. The prognosis is similar to that of conventional osteosarcoma. Although parts of this lesion show dense ossification, there is no overall indication of highly aggressive changes, so it is listed only as a differential diagnosis.
4. Chondrosarcoma or other cartilage-origin tumors:
   These typically show “ring” or “arc-like” calcifications on imaging and should be considered in older patients. However, in this case, the main finding is the dense osseous lesion with exophytic growth from the surface, and the cartilaginous features are not prominent.

3. Final Diagnosis

In summary, taking into consideration the patient's age, sex, a gradually enlarging painless mass, and imaging findings of dense ossification with exophytic growth, along with a relatively clear boundary between the lesion and the cortex, the most likely diagnosis is:

Parosteal Osteosarcoma.

For a definitive diagnosis, a pathological biopsy is recommended to further clarify the histological grade and specific characteristics of the tumor.

4. Treatment Plan and Rehabilitation

Treatment Strategy:

• Surgical resection is the main treatment: For surface osteosarcomas, the resection should ensure a tumor-free margin. Whether to perform a wide excision or consider joint replacement depends on the extent of the lesion, including cortical and medullary involvement.
• Neoadjuvant or adjuvant therapy: If pathological grading indicates high-risk characteristics (e.g., high-grade malignancy), adjuvant chemotherapy may be considered. For low-grade lesions, surgical removal is often the primary approach.
• Individualized comprehensive treatment: Preoperative assessment of overall health status and any comorbidities should be performed, and the plan should be formulated in accordance with imaging and pathological findings.

Rehabilitation and Exercise Prescription:

A gradual rehabilitation program after treatment (especially surgery) is crucial. The following is recommended:

1. Early Rehabilitation (0-6 weeks post-op):
   • Focus on surgical wound healing and initial restoration of joint range of motion. Under the guidance of a physician or physical therapist, passive or assisted-active joint exercises can be performed.
   • Depending on tolerance, conduct local isometric muscle contractions (avoiding large-range movements) to prevent muscle atrophy.
   • Avoid weight-bearing or excessive range-of-motion activities. Keep the affected limb safe and prevent secondary injury.
2. Mid-term Rehabilitation (6-12 weeks):
   • Once bone healing and soft tissue repair are confirmed, gradually introduce functional exercises with posture control, such as sitting and standing training and light weight-bearing ambulation (assistive devices may be needed).
   • Consider low-impact aerobic exercises, such as a stationary bike or an upper-body rowing machine. Training for overall cardiopulmonary function is particularly important.
   • Strengthen core and trunk stability exercises, steadily improving strength and coordination.
3. Late Rehabilitation (3 months to 1 year):
   • Based on satisfactory bone and soft tissue recovery, gradually increase weight-bearing on the affected limb, e.g., short-distance walking and squats.
   • Progressively increase the difficulty and frequency of strength and flexibility training, while closely monitoring for pain, swelling, or other issues, and adjust as needed.
   • Set individualized exercise goals according to the patient’s baseline fitness and functional needs, avoiding excessive loads.

Guided by the FITT-VP principle (frequency, intensity, time, type, progression, and individualization), it is suggested to start with training three to four times per week at a tolerable or light-to-moderate intensity for about 20-30 minutes each time, and then gradually increase the duration and intensity as rehabilitation progresses. If the patient has reduced bone density or lower cardiopulmonary function, initial loads should be decreased, and close communication with the primary physician and rehabilitation specialist is essential. Periodic imaging follow-up is also recommended.

5. Disclaimer

This report provides a reference medical analysis and should not replace a face-to-face consultation or the advice of a professional medical institution. Specific treatment regimens should be formulated by the patient in consultation with specialist physicians, taking into account individual circumstances.