Does synovial sarcoma of the knee joint typically present with pain or swelling first?

Synovial Sarcoma of the Knee: Pain Typically Precedes Swelling

Synovial sarcoma of the knee joint characteristically presents with pain first, often months to years before a swelling becomes apparent—a distinctive clinical pattern that differentiates it from most other sarcomas. 1

Key Clinical Presentation Pattern

• Pain precedes swelling in approximately 30% of synovial sarcoma cases, which is significantly more common than other sarcomas (3.6%) with an odds ratio of 11.68 1
• The mean duration of pain before swelling detection is 37 months (median 24 months, range 6-120 months), representing a prolonged premonitory phase 1
• This pain is often sharply localized and tender at the tumor site, though the character can be variable 1
• The pain may be non-mechanical in nature, similar to other bone sarcomas, and can occur at night 2

Clinical Significance and Diagnostic Challenges

• Swelling eventually develops but may only be detected through advanced imaging (MRI, CT, or ultrasound) rather than physical examination in early stages 1
• The prolonged pain-only phase leads to significant diagnostic delay, with a mean duration of 20 months from first presentation with pain until diagnosis 1
• In some cases presenting with chronic knee pain (12-18 months), patients develop flexion contracture before a mass is identified 3
• Calcification on X-rays during the pain-only phase may be misdiagnosed as benign lesions, further delaying correct diagnosis 1

Important Clinical Pitfalls

• The inconspicuous and diverse early symptoms make synovial sarcoma highly misdiagnosed 4
• When intra-articular, synovial sarcoma can mimic benign conditions like pigmented villonodular synovitis (PVNS) or localized tenosynovial giant cell tumor on imaging, especially when masses are less than 5 cm 3, 5
• MRI characteristics are often nonspecific for small intra-articular masses, showing well-circumscribed, homogeneous masses that are isointense to muscle on T1 and hyperintense on T2 sequences 3
• At exploratory surgery during the pain-only phase, there may be friable, vascular, or necrotic tissue without a well-defined tumor mass, which can mislead surgeons 1

Diagnostic Approach

• Maintain high clinical suspicion when patients present with persistent, localized knee pain that is non-mechanical or occurs at night, even without palpable swelling 2, 1
• Obtain MRI of the entire compartment with adjacent joints when malignancy cannot be excluded, as this is the best modality for detecting early synovial sarcoma 6
• Biopsy with SS18 gene rearrangement testing is mandatory for all patients in whom synovial sarcoma cannot be excluded, as this is the definitive diagnostic tool 4
• All biopsies must be performed at the facility that will provide definitive surgical management to avoid compromising limb-salvage surgery 2, 6

Prognostic Implications

• Early detection during the pain-only phase may enable diagnosis at a prognostically favorable early stage 1
• However, misdiagnosis or delayed diagnosis can have devastating consequences, as synovial sarcoma is highly malignant with poor prognosis 4
• Primary intra-articular origin may predispose to earlier presentation due to joint symptoms, potentially offering a window for earlier intervention 3
• Despite early symptoms, rapid progression can occur, with cases showing recurrence within 3 months of initial surgery and development of metastases leading to death within 20 months 5