Age / Sex : 26 / F

C.C.: Right knee pain and swelling for 1 year 

localized nodular synovitis

Discussion

Findings:
1. Plain radiography - No bony lesion - Normal joint space
2. MR - T1WI: mass lesion with low SI in anterior midportion of femorotibial joint - T2WI: mass lesion with low SI - Enhanced T1WI: mass lesion with well-enhancement
3. Arthroscopy - A well-localized, whitish, round mass (1.5x1cm) with stalk was located at anterior portion of ACL attachment site

Differential diagnosis :
- Localized nodular synovitis - PVNS (localized form) - Synovial chondroma - Cyclops lesion (localized form of anterior arthrofibrosis)

Diagnosis: Localized nodular synovitis

Discussion:
- benign proliferative disorder that originates from small area of the synovium
- most frequently in tendon sheaths of small joints of fingers and toes
- most common site: knee joint (predilection for infrapatellar fat body, suprapatellar recess, or bursa, pericruciate regions)
# Clinical manifestations
- pain, swelling or fullness, joint-line tenderness, restricted knee motion, palpable mass, locking of the knee
# MR imaging
- well-defined, small ovoid lesion or large polylobulated soft-tissue mass
- iso- or hyperintense signal intensity relative to skeletal muscle on T1WI
- variable signal intensity on T2WI
# Characteristics of localized nodular synovitis (vs. PVNS)
- smooth surface - involvement of small region of synovium
- small tumoral volume of hemosiderin
- absence of hemorrhagic joint effusion.
 - tends to grow outward, becoming pedunculated
# Treatment
- Surgical intervention
- Recurrence is rare unless the lesion is not excised completely

References:
1. Resnick D. Diagnosis of bone and joint disorders, 4th ed. Philadelphia: Saunders, 2002;3185-3186, 4246
2. Huang GS, Lee CH, Chan WP, Chen CY, Yu JS, Resnick D. Localized nodular synovitis of the knee: MR imaging appearance and clinical correlates in 21 patients. AJR Am J Roentgenol 2003;181(2):539-543