1. Imaging Findings

The patient is a 51-year-old female with pain and swelling in the left forearm for about 1 month. Based on the provided CT and MRI images, there is a well-defined low-density lesion within the bone of the ulna (or radius) in the left forearm:

• CT Findings: The lesion shows negative or relatively low CT values (the minimum measured value is approximately -254 HU), suggesting a fatty density. Its margins are relatively clear, with mild cortical expansion noted locally but no obvious sign of invasion into surrounding soft tissues.
• MRI Findings: On T1- and T2-weighted sequences, the lesion presents a high signal intensity similar to subcutaneous fat. On fat-suppression sequences, the signal is suppressed, consistent with fatty components. There is a slight change in local trabecular structure, and no obvious soft tissue mass or pathological fracture is identified.
• Surrounding Structures: The lesion is located within the medullary cavity, with mild cortical remodeling and expansion observed. No apparent extension into the surrounding muscle and fascial layers is seen, and there is no obvious compression of the adjacent neurovascular bundle.

2. Possible Diagnoses

Considering the patient’s clinical symptoms (local pain and swelling for 1 month) and the imaging findings, the differential diagnoses may include:

1. Intraosseous Lipoma
   Rationale: The lesion demonstrates typical fatty density or signal internally, with clear margins. CT values range from -100 to -300 HU, and MRI appearance is consistent with subcutaneous fat with complete suppression on fat-suppression sequences.
2. Aneurysmal Bone Cyst or Simple Bone Cyst
   Rationale: Both can appear as lucent bone lesions, but typically do not exhibit the classic fatty density on CT. MRI often shows fluid-like signals or septations, which generally do not fully suppress on fat-suppression sequences.
3. Bone Infarct
   Rationale: In late stages, bone infarction can lead to fatty changes and necrosis but often presents with irregular internal calcifications or a sclerotic rim. Also, marked bone expansion is not commonly associated with bone infarcts.
4. Non-ossifying Fibroma or Cartilage-Derived Lesions
   Rationale: These lesions may appear as lucent foci or calcifications within the bone, but their CT and MRI characteristics typically lack the classic fatty density or complete signal suppression that is indicative of fat.

3. Final Diagnosis

Considering the patient’s age, symptoms (local forearm pain and swelling), and the imaging findings (fatty density, complete suppression on fat-suppression sequences, clearly defined lesion margins, and no obvious soft tissue involvement) along with pathological results, the most likely diagnosis is:

Intraosseous Lipoma.

Although this lesion is relatively rare, the clinical, imaging, and pathological findings are all consistent with this diagnosis, providing sufficient grounds for confirmation.

4. Treatment Plan and Rehabilitation

4.1 Treatment Strategy

• Conservative Management: If the lesion is stable and symptoms are mild, observation with follow-up may be chosen, including regular imaging and clinical evaluations.
• Surgical Intervention: This is primarily indicated under the following circumstances:
  • Significant, persistent local pain or functional impairment
  • Imaging or pathology suggesting a potential malignant transformation (rare)
  • High risk of pathological fracture or existing fracture
  • Cosmetic concerns or compression of other structures
  Common surgical approaches include curettage followed by bone grafting or filling with bone chips to reduce fracture risk and stabilize the structure.

4.2 Rehabilitation and Exercise Prescription

Rehabilitation should follow an individualized approach and a gradual progression guided by the FITT-VP principle (Frequency, Intensity, Time, Type, Volume/Progression):

• Initial Phase (Postoperative or Early Symptom Relief):
  • Frequency: 3 times per week
  • Intensity: Low (isometric exercises of the affected limb, gentle grip exercises)
  • Time: 10-15 minutes per session
  • Type: Range of motion exercises, isometric muscle training; avoid weight-bearing and excessive forearm rotation
  • Progression: Focus on ensuring wound and bone healing before gradually increasing activity
• Mid-Stage (Bone Healing Stabilization):
  • Frequency: 3-4 times per week
  • Intensity: Moderate (may add light dumbbells or resistance bands)
  • Time: 20-30 minutes per session
  • Type: Rotational and flexion-extension strength training of the forearm, combined with functional exercises for the shoulder and elbow
  • Progression: Gradually increase load and number of sets based on recovery
• Late Stage (Functional Recovery and Strengthening):
  • Frequency: 4-5 times per week
  • Intensity: Gradual increase to moderate-high intensity
  • Time: 30-45 minutes per session
  • Type: Weight-bearing exercises (e.g., light wrist flexion-extension, forearm pronation-supination), with added proprioceptive and balance training
  • Progression: Assess bone healing and muscle strength to prevent reinjury caused by overtraining

During the rehabilitation process, closely monitor local pain, swelling, or functional changes. If significant discomfort or recurrent swelling occurs, discontinue activities and seek timely re-evaluation.

Disclaimer

This report is based on the current imaging and clinical information and is for reference only. It cannot replace an in-person consultation or professional medical advice. If you have any questions or experience changes in symptoms, please seek prompt medical attention for a face-to-face professional evaluation.