Computed tomography scanning in the diagnosis of lower extremity phlebolymphedema.

Objectives: Phlebolymphedema, the most common cause of secondary lymphedema in Western societies, seldom gets the attention it deserves. Diagnosis is often missed and when evaluated is through lymphoscintigraphy (LSG) which is cumbersome. This study aims to assess the role of computed tomography (CT) scanning in the diagnosis of phlebolymphedema of the lower extremities by comparing CT characteristics to the International Society of Lymphology (ISL) grading system and LSG.

Methods: Patients presenting with chronic venous disease who underwent a CT scan and LSG of the lower extremities (diagnostic testing) formed the study cohort. Three assessors blinded to the patients' ISL stage and lymphoscintigraphy results evaluated the CT for skin thickening (present/absent), subcutaneous interstitial edema (honeycombing; graded 0-2), and muscle compartment edema (graded 0-2), in the thigh (20 cm above apex of patella), leg (10 cm below apex of patella) and ankle (5 cm above lateral malleolus). Agreement from 2 of 3 raters determined the value used for analysis. Additionally, the final score used for each variable for each limb was determined by taking the most severe value of the three levels. The three CT variables were then compared independently and together to ISL stage and LSG to determine their diagnostic potential for phlebolymphedema. Also assessed was the severity of each CT variable across each limb in addition to the evaluation of the extent of their interrater agreement.

Results: Of the 35 patients (50 limbs), 28 were female, with left laterality noted in 22 limbs. CEAP clinical class for the cohort included C0-2: 4 limbs (8%), C3: 13 limbs (26%), C4: 17 limbs (34%), C5: 9 limbs (18%), C6: 7 limbs (14%). 31 limbs underwent stenting for CIVO after having failed conservative therapy. Of the 50 limbs, 8 (16%) were ISL stage 0, 10 (20%) ISL stage 1, 2 (4%) ISL stage 2, and 30 (60%) ISL stage 3. With LSG, 6 (12%) had a normal study, 21 (42%) mild disease, 0 (0%) moderate disease, and 23 (46%) severe disease. Correlation between LSG and ISL stage was poor (r = 0.18; p=0.20). With ISL Stage as reference, sensitivity/specificity/accuracy of CT in diagnosing phlebolymphedema: skin thickening (95%/75%/92%), honeycombing (100%/0%/84%), muscle compartment edema (100%/0%/84%), any one CT variable (100%/0%/84%), any two CT variables (100%/0%/84%) and all 3 CT variables (93%/63%/88%). With LSG as reference, sensitivity/specificity/accuracy of CT in diagnosing phlebolymphedema: skin thickening (82% /0%/72%), honeycombing (100%/0%/88%), muscle compartment edema (100%/0%/88%), any one CT variable (100%/0%/88%), any two CT variables (100%/0%/88%) and all 3 CT variables (82%/0%/72%). For CT variables, there was no significant difference between skin thickening in the thigh versus calf versus ankle (p=0.5). Muscle compartment edema however worsened from thigh to calf (p<0.0001) without a difference between calf and ankle (p=0.3). The severity of honeycombing was worst in the ankle and least in the thigh with a significant difference between all 3 sites (p = 0.008). The interrater agreement (Kappa statistic) varied from 0.2 for skin thickening to 0.7 for honeycombing.

Conclusions: CT scanning can be a screening tool for phlebolymphedema in the lower extremities. However, such a diagnosis depends on the reference standard used, ISL system versus lymphoscintigram. While skin thickness offered the highest sensitivity, specificity, and accuracy when the ISL system was used, honeycombing or muscle compartment edema had high sensitivity and accuracy but low specificity when LSG was used as the reference. Factoring in interrater agreement as well, honeycombing was noted to be the best CT variable to diagnose phlebolymphedema.