Summary A metal-on-metal (MoM) THA pseudotumor, also known as aseptic lymphocyte-dominant vasculitis-associated lesion (ALVAL), is a mass-forming tissue reaction caused by metal-on-metal wear Diagnosis involves obtain meta-subtraction MRI studies in the setting of elevated serum metal ion levels (cobalt, chromium) Treatment is typically revision arthroplasty for symptomatic pseudotumor with elevated metal ions Epidemiology Incidence 10-15% of patients with MoM THA have a pseudotumor 45-50% of revisions in patients with MoM THA are due to pseudotumor or adverse local tissue reaction Risk factors elevated cobalt and chromium levels female gender high acetabulum inclination angle > 55° Etiology Pathophysiology mechanism two different mechanisms have been proposed for formation of pseudotumors: login to view 2 more bullets variability in distribution of metal debris, degree of necrosis, and number, type, and arrangement of inflammatory cells macrophages and lymphocytes are present in all cases with lymphocytes being predominant login to view 2 more bullets Presentation History patient may complain of gradual onset of symptoms or a sudden inciting pain in the groin Symptoms common symptoms may be asymptomatic groin pain trendelenburg gait Physical Exam inspection soft tissue masses around the hip may be present neurovascular usually normal provocative tests groin pain with flexion, IR and adduction groin pain with rising from a chair Imaging Radiographs recommended views AP pelvis, AP and lateral of affected hip findings will show metal-on-metal THA necessary to rule out peri-prosthetic fractures as source of pain may show peri-prosthetic bony erosion, commonly seen in calcar region MRI with Metal Artifact Reduction Sequence (MARS) indications normal radiographs in the setting of elevated metal ion levels (cobalt, chromium) findings a pseudotumor will appear like a fluid collection or solid mass in periprosthetic soft tissues T1 weighted images will show signal similar to bladder contents (transudate) T2 weighted images will generally show hyperintensity as compared to muscle and may be heterogenous or homogenous login to view 1 more bullet Studies Serum labs WBC, ESR and CRP metal ion levels (cobalt, chromium) serum metal ion concentration highest at 12-24 months following index surgery login to view 1 more bullet values > 7 parts per billion (ppb, or ug/L) generally an indication for advanced imaging with MRI Invasive studies Hip aspiration synovial fluid analysis will allow for differentiation of a metallosis from periprosthetic infection gross appearance of metallosis generally described as "dishwater fluid" with watery, grayish and hazy appearance manual cell count necessary login to view 1 more bullet Treatment Nonoperative observation indications login to view 1 more bullet outcomes login to view 1 more bullet Operative revision THA to ceramic-on-polyethelyne components indications login to view 3 more bullets outcomes login to view 4 more bullets Techniques Observation technique in the asymptomatic patient, serial hip radiographs to assess for wear, or component loosening can be performed Revision THA to ceramic-on-polyethelyne components approach depends on location of tumor and surgeon preferene login to view 1 more bullet technique can be single stage or 2 stages depending on surgeon preference or presence/concern of infection depend on bone loss, abductor defiency and soft tissue damage constraint liners may be required if severe abductor deficiency is present complications instability deep infection aseptic loosening persistent iliopsoas tendonitis persistent metal related reaction Complications Repeat revision THA incidence 14-20% of revision THAs performed due to a MoM pseudotumor require a 2nd operation within 5 years treatment revision THA to address reason for repeat failure Pseudotumor induced femoral nerve palsy incidence rare, only case reports noted treatment decompression and revision THA to ceramic-on polyethelyne components