Lump Mass Musculoskeletal

Introduction to MSK Masses for MCCQE1

The evaluation of a musculoskeletal (MSK) lump or mass is a high-yield topic for the MCCQE1. Candidates are expected to differentiate between benign and malignant lesions, recognize “red flags” requiring urgent referral, and understand the appropriate diagnostic pathway within the Canadian healthcare system.

Under the CanMEDS framework, the Medical Expert role requires a structured approach to these presentations to avoid the catastrophic error of an “unplanned excision” of a sarcoma.

Clinical Assessment

History: Key Distinguishers

Age is the single most important determinant of the differential diagnosis for bone and soft tissue tumors.

• Pediatric (< 20 years): Primary bone tumors (Osteosarcoma, Ewing Sarcoma).
• Adult (20–40 years): Giant cell tumor, benign soft tissue masses.
• Older Adult (> 40 years): Metastatic disease, Multiple Myeloma, Chondrosarcoma.

Red Flags in History

• Pain: Night pain, rest pain, or pain unrelated to activity.
• Growth: Rapid increase in size.
• Constitutional Symptoms: Fever, weight loss, night sweats (B symptoms).
• History of Cancer: Previous malignancy (increases risk of metastasis).

Physical Examination

Evaluate the mass using the standard inspection and palpation techniques.

Differential Diagnosis

The differential diagnosis is vast. Categorizing by tissue origin and behavior is essential for MCCQE1 preparation.

Diagnostic Approach

Follow this stepwise approach to maximize your score on MCCQE1 clinical reasoning cases.

Canadian Guidelines & Management

In Canada, the management of suspected sarcomas is regionalized.

Referral Pathways

Any patient with a soft tissue mass that is:

1. Deep to deep fascia, OR
2. > 5 cm in diameter, OR
3. Rapidly growing

…requires urgent referral to a tertiary Sarcoma Centre (e.g., Mt. Sinai in Toronto, Maisonneuve-Rosemont in Montreal, BC Cancer Agency).

Management Principles

Key Points to Remember for MCCQE1

• Age is key: A destructive bone lesion in a 65-year-old is metastasis or myeloma until proven otherwise. In a 15-year-old, it is Osteosarcoma or Ewing’s.
• Mnemonic for Bone Mets: BLT with a Kosher Pickle (Breast, Lung, Thyroid, Kidney, Prostate).
• Mnemonic for Aggressive X-ray features: Sunburst (Osteosarcoma), Onion Skin (Ewing’s), Codman’s Triangle (Either).
• Lipoma vs. Liposarcoma: You cannot distinguish these solely on physical exam if the mass is deep or large. MRI is required.
• Biopsy Rule: The surgeon who will perform the definitive resection should perform (or direct) the biopsy.

Sample Question

Clinical Scenario

A 55-year-old male presents to his family physician with a painless lump in his right thigh. He noticed it 3 months ago, and he believes it has increased in size. He has no history of trauma. On physical examination, there is a firm, non-tender mass located in the anterior thigh, measuring approximately 8 cm in diameter. The mass appears to be deep to the subcutaneous tissue and is fixed to the underlying muscle. There is no overlying erythema or warmth. Range of motion of the knee and hip is preserved.

Question

Which one of the following is the most appropriate next step in the management of this patient?

• A. Reassure the patient and observe for another 3 months
• B. Perform an incisional biopsy in the office
• C. Prescribe a course of oral antibiotics
• D. Order a Magnetic Resonance Imaging (MRI) of the thigh
• E. Refer for immediate surgical excision (lumpectomy)

Explanation

The correct answer is:

• D. Order a Magnetic Resonance Imaging (MRI) of the thigh

Detailed Analysis

• Why D is correct: This patient presents with a “red flag” soft tissue mass: it is large (> 5 cm), deep (subfascial), and growing. In an adult, a soft tissue mass with these characteristics is a soft tissue sarcoma until proven otherwise. The most appropriate diagnostic step to characterize the lesion and stage it locally is an MRI with contrast. This allows for assessment of the tumor’s relationship to nerves, vessels, and bone.

• Why A is incorrect: Observation is inappropriate for a mass that is growing and > 5 cm. Delay in diagnosis of a sarcoma can lead to metastasis and poor outcomes.

• Why B is incorrect: Performing a biopsy in a primary care setting is contraindicated. Poorly planned biopsies can contaminate tissue planes, making subsequent limb-salvage surgery impossible and potentially necessitating amputation. Biopsies should be performed by the treating surgical oncologist or interventional radiologist at a sarcoma center.

• Why C is incorrect: There are no signs of infection (erythema, warmth, fever, extreme tenderness). Antibiotics are not indicated.

• Why E is incorrect: “Unplanned excision” or “shelling out” a sarcoma is a major error. Without appropriate imaging (MRI) and wide margins, the tumor will likely recur locally, and the initial surgery will have spread tumor cells into the hematoma cavity, complicating future definitive surgery.

References

1. Medical Council of Canada. MCCQE Part I Objectives: Musculoskeletal System.
2. CanMEDS Framework. Royal College of Physicians and Surgeons of Canada.
3. Blackstein, M., et al. “Canadian Sarcoma Group Guidelines.” Current Oncology.
4. Toronto Notes 2024. Orthopedics Chapter: Bone and Soft Tissue Tumors.
5. UpToDate. Clinical presentation, histopathology, diagnostic evaluation, and staging of soft tissue sarcoma.