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 with 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 LSG results evaluated the CT for skin thickening (present/absent), subcutaneous interstitial edema (honeycombing; graded 0-2), and muscle compartment (MC) 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 two of the three 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 with 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 inter-rater agreement.

RESULTS

Of the 35 patients (50 limbs), 28 were female, with left laterality noted in 22 limbs. Clinical, Etiological, Anatomical, and Pathophysiological clinical class for the cohort included C0 to 2, 4 limbs (8%); C3, 13 limbs (26%); C4, 17 limbs (34%); C5, 9 limbs (18%); and C6, 7 limbs (14%). Thirty-one limbs underwent stenting for chronic iliofemoral venous obstruction 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 = .20). With ISL stage as a reference, the sensitivity, specificity, and accuracy of CT in diagnosing phlebolymphedema were as follows: skin thickening (95%/75%/92%), honeycombing (100%/0%/84%), MC edema (100%/0%/84%), any one CT variable (100%/0%/84%), any two CT variables (100%/0%/84%), and all three CT variables (93%/63%/88%). With LSG as a reference, the sensitivity, specificity, and accuracy of CT in diagnosing phlebolymphedema were as follows: skin thickening (82%/0%/72%), honeycombing (100%/0%/88%), MC edema (100%/0%/88%), any one CT variable (100%/0%/88%), any two CT variables (100%/0%/88%), and all three CT variables (82%/0%/72%). For CT variables, there was no significant difference between skin thickening in the thigh vs calf vs ankle (P = .5). MC edema, however, worsened from thigh to calf (P < .0001) without a difference between the calf and the ankle (P = .3). The severity of honeycombing was worst in the ankle and least in the thigh, with a significant difference between all 3 sites (P = .008). The inter-rater agreement (kappa statistic) varied from 0.2 for skin thickening to 0.7 for honeycombing.

CONCLUSIONS

CT scanning can be used as a screening tool for phlebolymphedema in the lower extremities. However, such a diagnosis depends on the reference standard used, ISL stage vs lymphoscintigram. Although skin thickness offered the greatest sensitivity, specificity, and accuracy when the ISL stage was used, honeycombing or MC edema had high sensitivity and accuracy but low specificity when LSG was used as the reference. Factoring in inter-rater agreement as well, honeycombing was noted to be the best CT variable to diagnose phlebolymphedema.