Popliteal Node Visualization During Standard Pedal Lymphoscintigraphy for a Swollen Limb Indicates Impaired Lymph Drainage

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1 Nuclear Medicine and Molecular Imaging Original Research Burnand et al. Popliteal Nodes in Lymphoscintigraphy Nuclear Medicine and Molecular Imaging Original Research Katherine M. Burnand 1 Daphne M. Glass 2 Sumati Sundaraiya 1 Peter S. Mortimer 3 A. Michael Peters 1,2 Burnand KM, Glass DM, Sundaraiya S, Mortimer PS, Peters AM Keywords: lipedema, lymphedema, lymphoscintigraphy, lymph nodes, popliteal nodes, 99m Tc-nanocolloid DOI: /AJR Received February 1, 2011; accepted after revision July 20, Department of Nuclear Medicine, Royal Sussex County Hospital, Brighton, Sussex Medical School, Audrey Emerton Bldg, Eastern Rd, Brighton BN2 5BE, United Kingdom. Address correspondence to A. M. Peters (a.m.peters@bsms.ac.uk). 2 Department of Nuclear Medicine, Harley Street Clinic, London, United Kingdom. 3 Department of Medicine, St. George s Hospital, London, United Kingdom. AJR 2011; 197: X/11/ American Roentgen Ray Society Popliteal Node Visualization During Standard Pedal Lymphoscintigraphy for a Swollen Limb Indicates Impaired Lymph Drainage OBJECTIVE. The objective of our study was to examine the frequency and significance of visualization of popliteal nodes during lymphoscintigraphy for the investigation of lower extremity swelling. MATERIALS AND METHODS. Technetium-99m labeled nanocolloid was injected subcutaneously in the first web spaces of both feet of 204 consecutive patients (69 males, 135 females; age range, years) undergoing routine, clinically indicated lymphoscintigraphy; imaging was performed 5, 45, and 150 minutes after injection. The patients were asked not to undertake any vigorous exercise between the injection and completion of imaging. RESULTS. No popliteal nodes were visualized in 29 patients in whom there was no evidence of lymphedema on clinical or lymphoscintigraphic examination (group 1). Unilateral or bilateral popliteal nodes were visualized in 10 of 39 patients (25.6%) with clinical evidence of lymphedema but normal lymphoscintigraphy findings (group 2) (p < vs group 1). In 136 patients with clinical evidence of lymphedema and abnormal lymphoscintigraphy findings (group 3), unilateral or bilateral popliteal nodes were visualized in 59 (43.4%) (p < vs group 1). Popliteal nodes were visualized in 40 of 73 limbs with dermal backflow (54.8%) and 42 of 335 limbs without dermal backflow (12.5%) (p < ). CONCLUSION. Popliteal node visualization after subcutaneous foot web space injection is an important sign of abnormal lymphatic function in patients with clinical lymphedema of the lower extremities. L ymphoscintigraphy of the lower limbs is routinely performed for the investigation of a swollen limb or recurrent cellulitis. Limb swelling results from increased deposition of fat, such as in lipedema, or from fluid overload, which may be the result of increased capillary fluid filtration (as in venous disease) or impaired lymph drainage, which may be primary or secondary. Even if the swelling is the result of increased capillary fluid filtration, the fluid overload is appropriately termed lymphedema because the lymphatic fails to accommodate the increased filtrate. Over time, the lymphatic failure progresses from a functional failure to a permanent and irreversible failure [1]. The cause of lymphedema is often multifactorial [2]. Lymphoscintigraphy not only confirms lymphatic failure when abnormal but also can provide useful information about the pathophysiology and mechanism of lymphatic failure. For example, in genetic forms of lymphedema, such as Milroy dis- ease, there is a failure of initial lymphatic uptake as a result of mutations in the gene for vascular endothelial growth factor receptor 3 [3]. In lymphedema distichiasis syndrome, which is caused by mutations in FOXC2, the mechanism is lymph reflux due to lymphatic valve failure and the lymphoscintigraphic images are characteristic [4]. Lymphoscintigraphy for sentinel lymph node (SLN) identification in patients with lower limb extremity melanoma has shown that popliteal nodes may take up tracer [5 8], indicating subfascial (deep) lymphatic vessel transport. Popliteal node visualization during lymphoscintigraphy for the investigation of a swollen lower extremity, therefore, has come to be regarded as a normal variant [9]. However, tracer administered around the lateral foot and ankle, as given for SLN identification, may drain via the deep route, but tracer administered into the web spaces, under normal circumstances, follows an epifascial route. Whereas the injection site for SLN identification in patients with primary tumor AJR:197, December

2 Burnand et al. varies according to the site of the primary tumor, injections for the investigation of lower limb swelling are usually into a web space. The aim of this study was to determine the frequency of popliteal node uptake after web space injection for the investigation of lower limb swelling and examine whether popliteal node uptake can be regarded as a normal lymphoscintigraphic variant. Materials and Methods Patients The study group for this retrospective study was 204 patients (69 males, 135 females; age range, years) seen consecutively in a single lymphedema clinic and referred for routine lower limb lymphoscintigraphy after clinical examination by a single consultant clinician with more than 25 years experience in lymphedema care. Because this study is a retrospective analysis of an anonymous database of clinical referrals, the local institutional review board advised that submission for ethical approval was not required. Lymphoscintigraphy Technetium-99m labeled nanocolloid (Nanocoll, GE Healthcare) was injected by one of two operators, usually with the other in attendance, subcutaneously (~ 20 MBq in 0.2 ml per limb) into the dorsum of the first web space of the foot using a 1-mL syringe and a 25-gauge needle. The needle was 8 mm long and was inserted to a depth of 4 mm. The material was prepared according to the manufacturer s guidelines, which state that 95% of the particles have a size of less than 80 nm. Penetration of the needle into a blood vessel was excluded by careful aspiration before injection. The injection, being subcutaneous, produced a bubble in the skin rather than a blister. No massage, leg elevation, or warm compresses were used after injection. Half-body anterior and posterior images from the upper abdomen to the toes were obtained with a large-fov gamma camera. Imaging began immediately after tracer injection and 45 and 150 minutes later. Each image took 10 minutes to acquire, so the first image is described as the 5-minute image. Patients were encouraged to take a short walk between the 45-minute and 2.5-hour scans but were told not to undertake strenuous exercise. A popliteal node was considered present when lymphoscintigraphy showed at least one discrete fo- TABLE 1: Brief Clinical Details of Group 1 Patients With No Clinical Evidence of Lymphedema and With Normal Lymphoscintigraphy Findings Presentation Other Clinical Information Final Diagnosis Family history of leg swelling Normal Polycystic ovary syndrome, lipedema Bilateral knee effusions Arthritis, obesity Rheumatic swelling Family history of big legs Hamartoma Normal Short stature Normal Dercum disease Prader-Willi syndrome Obesity Family history of lipedema, obese Normal Bilateral swelling Family history of lipedema, anorexia Normal Lipodermatosclerosis Minor transient leg swelling Leg swelling after flights Normal Painful legs Dercum disease Scrotal edema Sudden onset of rash and scrotal edema Postinfection and injury Facial lymphedema Granulomatous rosacea Right arm swelling Psoriasis Arthritis-induced edema Arm swelling Breast implants Normal History of left foot swelling Previous cellulitis Isolated episode Panniculitis, small venous varicosities Erythema nodosum Foot swells in hot weather Normal Family history of lipedema Hypothyroidism, family history of big legs 1444 AJR:197, December 2011

3 Popliteal Nodes in Lymphoscintigraphy cus of activity of a size commensurate with a lymph node at the level of the knee between the primary injection site and the draining ilioinguinal lymph nodes. The percentage of administered radioactivity present in regions of interest placed over the right and left ilioinguinal nodes was recorded in separate dedicated static gamma camera images obtained at about 60 and 180 minutes after injection in 148 patients. Counts were corrected for background and radionuclide decay but not for depth. TABLE 2: Final Diagnoses by Patient Group Fig. 1 Normal lymphoscintigraphy findings in 40-yearold woman with hamartoma on left leg. Lymphoscintigraphy was performed to exclude lymphatic involvement before surgery. Note how epifascial trunks track up medial aspect of lower extremity in region of saphenous vein. RT = right, LT = left, MIN = minutes. Clinical Criteria A diagnosis of lymphedema was initially made on clinical examination. Not all patients had definite clinical evidence of lymphedema but nevertheless still had been referred for lymphoscintigraphy for confirmation of normal lymphatic function. In order for a patient to be described as showing no clinical evidence of lymphedema, both lower limbs had to reveal no abnormalities to suggest an underlying lymphatic abnormality specifically, no pitting edema or any skin change such as dermatosclerosis, hyperkeratosis, or increased skin turgor [1]. The Kaposi-Stemmer sign, a sensitive clinical sign of lymphedema in which it is not possible to pinch a fold of skin at the base of the second toe on the dorsum of the foot [10 12], was also negative for all patients classified as showing no clinical evidence of lymphedema. Lymphoscintigraphy Criteria Abnormal scan findings were characterized as major or minor (Appendix 1). A limb was defined as abnormal if at least one major criterion or two or more minor criteria were fulfilled. Because the purpose of the study was to assess the diagnostic significance of popliteal node visualization, it was not included as an interpretative criterion. Statistics Proportionate analysis [13] was used to determine the significance of the difference between paired proportions and the chi-square test for the association between popliteal node visualization and skin rerouting. Results A total of 29 patients with varying degrees of tissue swelling or who were considered to be at risk for developing lymphatic dysfunction were thought to have no clinical evidence of lymphedema (group 1; Table 1). Lymphoscintigraphy was performed to confirm normal lymphatic function in these patients, and findings were normal in all 29 cases (Fig. 1). Thirteen of these 29 patients had a final diagnosis of lipedema. Of the 175 patients with clinically apparent lymphedema, 39 had normal findings on lymphoscintigraphy (group 2) and 136 had abnormal findings on lymphoscintigraphy (group 3). The final diagnoses in terms of whether the patient had primary lymphedema, secondary lymphedema, or a combination of the two are summarized for each patient group in Table 2. No popliteal nodes were visualized in group 1 patients (n = 29) in contrast to the patients with clinically apparent lymphedema (groups 2 and 3; n = 175) in whom popliteal nodes were visualized in a total of 69 patients (39.4%; p < vs group 1) (Fig. 2). In the group of 39 patients with clinical evidence of lymphedema but normal scintigraphy findings (group 2), popliteal nodes were visualized in 10 (unilaterally in nine; Table 3) (25.6%; p < vs group 1). In the 136 patients with clinical evidence of lymphedema and abnormal scintigraphy findings (group 3), popliteal nodes were visualized in 59 (43.4%; p < vs group 1). In these 136 patients, the scintigraphic findings were abnormal bilaterally in 64 patients (of whom 29 had unilateral [n = 16] or bilateral [n = 13] popliteal node visualization) and were abnormal unilaterally in 72 patients (of whom 30 had popliteal node visualization; Table 3). In four of these 72 patients, popliteal nodes were visualized in the limb with normal scintigraphy findings (Table 2). Thus, if popliteal node visualization had been considered abnormal, 15 of 150 limbs (10.0%) with otherwise normal scintigraphy findings in patients with abnormal clinical findings would have been rediagnosed as abnormal. Likewise, on a patient-by-patient basis, scintigraphy findings would have been considered abnormal in 10 of the 39 patients (25.6%) with abnormal clinical findings but otherwise normal scintigraphy findings. Rerouting of lymph through the skin, termed dermal backflow (Fig. 3), was diagnosed when tracer was clearly seen to enter the small lymphatic vessels of the skin, Group No. No. of Patients Primary Lymphedema Secondary Lymphedema Primary and Secondary Lymphedema No Diagnosis a Total a Resolved. AJR:197, December

4 Burnand et al. giving the impression of encasement of the limb in radioactivity. Dermal backflow was identified in one or both lower limbs of 64 of the 136 group 3 patients (47.1%). Popliteal nodes were visualized on one or the other side in 36 of these 64 patients (56.3%). In contrast, popliteal nodes were visualized on one or the other side in only 19 of 72 group 3 patients (26.4%) with no skin rerouting (p < 0.001). On a limb-by-limb basis, there was a very strong association between skin rerouting and popliteal node visualization (n = 408; p < ) (Fig. 4 and Table 4). Fig. 2 Abnormal lymphoscintigraphy findings in 44-year-old woman with swelling of right leg and clinical diagnosis of lymphedema. Image clearly shows popliteal node (open arrowhead) on left. Note that ilioinguinal node activity is asymmetric (reduced on right) and that deep lymphatic trunk is visible on left. On right, lymph rerouting through skin ( dermal backflow ) of lateral aspect of lower leg and ankle (solid arrowhead) and two faint popliteal nodes (open arrowhead) are seen. RT = right, LT = left, MIN = minutes. Discussion Lymphoscintigraphy of the lower extremities is generally performed for investigation of a swollen limb or to guide SLN biopsy. Popliteal nodes are in lymphatic chains that accompany the deep veins and are consequently consistently seen after subfascial injection, such as into the gastrocnemius muscle. Subcutaneous and intradermal injections into the web spaces, in contrast, deliver tracer to the epifascial lymphatic system, which normally remains separate from and does not mix with the deep system [14]. Much of our understanding of lower limb lymphatic anatomy is based on contrast-enhanced lymphography [14] and, more recently, on SLN biopsy results in patients with melanoma. Although Hatta et al. [15] visualized popliteal nodes in five of 14 patients (36%) undergoing SLN biopsy for melanoma, other groups have reported a lower incidence of popliteal lymph node visualization of between 3.2% and 7.2% [5 8]. In the study of Hatta et al., all five patients in whom popliteal nodes were visualized received the primary injection into the heel and the lateral foot or malleolus, suggesting a lymph route that from those sites is diverted into the deep system. This finding is consistent with contrast-enhanced lymphography, which showed that injection into these sites accesses the deep system. Thompson et al. [16] went further and suggested that drainage to popliteal nodes from a superficial injection is not restricted to the posterolateral aspect of the heel and lateral malleolus. Thompson et al. did not mention, however, whether such patients may have had concurrent secondary lymphedematous changes in their lower legs giving rise to an aberrant lymph drainage route. In any event, because the site of injection varies for SLN biopsy, the significance of popliteal node visualization in this context is less relevant than in the context of lymphoscintigraphy for a swollen limb for which the injection site is constant. Although popliteal node visualization after superficial injection for melanoma SLN biopsy appears to be unusual (but not rare), metastases in popliteal nodes are extremely rare [15, 16]. In a retrospective study of 4262 patients with primary melanomas of the lower leg, only 13 (0.3%) had popliteal node metastases [16]. Moreover, five of the patients in that series also had metastatic groin node disease detected at the time of or before the presentation of popliteal metastases, so these popliteal node metastases may have been the result of lymph diversion through the deep system. Thus, even allowing that many patients in such a large series may have had primary lymphatic abnormalities with rerouting through the deep system before they developed melanoma, such a rare incidence of popliteal metastases represents a conundrum. The 29 patients in this series who had normal findings on lymphoscintigraphy and no definite clinical evidence of lymphedema were nevertheless clinically referred for lymphoscintigraphy and were, therefore, not healthy subjects. They included patients with lipedema or obesity, family members of patients with lymphedema, or patients with swelling elsewhere (e.g., upper limb and face) and are listed in Table 1. They therefore represent a control group rather than a healthy group. Notably, Szuba et al. [17] emphasized that lymphedema can be surprisingly difficult to diagnose clinically, so these patients were still referred to undergo lymphoscintigraphy to confirm normal lymphatic function. Many (n = 13) of these 29 patients had a final diagnosis of lipedema (Table 1), a genetic disorder distinct from obesity, that gives rise to heavy deposition of fat in the lower limbs and is known to be associated with normal TABLE 3: Breakdown of Patients on the Basis of Clinical Findings, Lymphoscintigraphy Findings, and Popliteal Node Visualization No. of Patients (Group) Clinical Findings Scintigraphy Findings Popliteal Node Visualization (No. of Patients) 29 (Group 1) Normal Normal 0 39 (Group 2) Abnormal Normal 10 Bilateral, 1 Unilateral, (Group 3) Abnormal Abnormal Bilateral Unilateral 30 a a Including four otherwise scintigraphically normal limbs AJR:197, December 2011

5 Popliteal Nodes in Lymphoscintigraphy lymph drainage and normal lymphoscintigraphy findings in the initial stages [18]. Lymphoscintigraphy of patients with lipedema is performed to exclude lymph drainage abnormalities because the condition may lead to lymphedema. However, none of these 13 patients with lipedema had abnormal findings on lymphoscintigraphy. Notably, in contrast, there were several patients with lipedema in group 3 in this study who did have lymphatic dysfunction on scintigraphic examination. In general, however, the lack of a group of healthy volunteers must be acknowledged as a limitation of this study. Weissleder and Weissleder [9] performed lymphoscintigraphy of 19 healthy volunteers and visualized 1 3 popliteal nodes per limb (mean, 1.8). In contrast, popliteal nodes were not seen in any of our 29 patients in whom there was no clinical or lymphoscintigraphic evidence of lymphatic dysfunction. Whereas our subjects were told not to undertake any strenuous exercise, the subjects in the Weissleder study had electric foot ergometry operating at 30 cycles per minute Fig. 3 Abnormal lymphoscintigraphy findings in 18-year-old man with right lower limb swelling. Image shows marked lymph rerouting through skin of right lower limb. Left limb was clinically and lymphoscintigraphically normal. Final diagnosis was ilioinguinal nodal sclerosis. RT = right, LT = left, MIN = minutes. TABLE 4: Association on a Limb-by-Limb Basis Between Lymph Rerouting Through the Skin ( Dermal Backflow ) and Popliteal Node Visualization (Rerouting Through the Deep System) No. (%) of Limbs Imaging Finding No Skin Rerouting Skin Rerouting Total No. No popliteal nodes visualized 293 (90) 33 (10) 326 Popliteal nodes visualized 42 (51) 40 (49) 82 Total 335 (82) 73 (18) 408 and were also asked to climb five flights of stairs between sequential images. This difference in lymphoscintigraphy results raises the concern that exercise results in rerouting of lymph through the deep system possibly as a result of increased blood flow, capillary filtration, and lymph production and masks a potentially useful clue of lymphatic dysfunction. If exercise does result in diversion of lymph to the deep system, it would make the rarity of popliteal node metastases, mentioned earlier, even more difficult to explain. Not only were popliteal nodes seen significantly more frequently in patients with abnormal compared with normal findings on scintigraphy, there was also a strong and positive association between lymph rerouting through the skin (i.e., dermal backflow) and popliteal node visualization. One might have speculated the opposite: That disturbances in the deep system result in dermal rerouting, whereas disturbances in the epifascial system result in deep rerouting, giving rise to a mutually exclusive pattern of rerouting. The positive association, however, was not complete, suggesting that this aspect of lymph rerouting deserves further study to determine whether a predominant pattern of rerouting provides any further useful information about the nature of a lymphatic abnormality. With the exception of the association between rerouting of lymph through the skin with that through the deep system, our analysis was on a patient-by-patient basis rather than limb by limb. We chose to report our results on a per-patient basis because of the likelihood that lymphatic dysfunction, when present, is bilateral [19]. This tendency is likely to be true for secondary as well as primary (constitutional) lymphedema. Thus, consider breast cancer related lymphedema. Axillary lymph node dissection results in breast cancer related lymphedema in only 25% of patients [20]. Either the 75% who do not get breast cancer related lymphedema develop protective mechanisms or the 25% who do get it already have, constitutionally, a system in which lymph drainage capacity is readily exceeded by capillary filtration. The latter theory is supported by recently published evidence [21]. A primary cause for lymphedema in the current study was thought to be present in 61% of all patients Fig. 4 Abnormal lymphoscintigraphy findings in 67-year-old woman with bilateral limb swelling and documented venous disease. Image shows marked lymph rerouting through skin of right lower limb (solid arrowhead) accompanied by rerouting of lymph through deep system. Deep lymphatic trunk and several popliteal nodes (open arrowhead) are visible. Swollen left limb was lymphoscintigraphically normal. Final diagnosis was bilateral mixed lymph venous disease. RT = right, LT = left, MIN = minutes. AJR:197, December

6 Burnand et al. (71% after exclusion of group 1 patients). These results support the notion that, in general, for lymphedema to arise from a secondary cause, there needs to be preexisting latent primary lymphedema. In conclusion, visualization of the popliteal nodes after injection into a web space for the investigation of lower limb swelling indicates lymph rerouting through the deep system and supports a diagnosis of abnormal lymphatic function. Patients undergoing lymphoscintigraphy should be encouraged to avoid strenuous exercise between injection and imaging; otherwise, popliteal node visualization may be masked as a useful sign of abnormal function. References 1. Mortimer PS, Levick JR. Chronic peripheral oedema: the critical role of the lymphatic system. Clin Med 2004; 4: Kerchner K, Fleischer A, Yosipovitch G. Lower extremity lymphedema. J Am Acad Dermatol 2008; 59: Mellor RH, Hubert CE, Stanton AWB, et al. Lymphatic dysfunction not aplasia underlies Milroy disease. Microcirculation 2010; 17: Mellor RH, Tate N, Stanton AWB, et al. Mutations in FOXC2 in humans (lymphoedema distichiasis syndrome) cause lymphatic dysfunction on dependency. J Vasc Res 2011; 48: APPENDIX 1: Lymphoscintigraphy Criteria [17] 5. Uren RF, Howman-Giles R, Thompson JF, et al. Interval nodes: the forgotten sentinel nodes in patients with melanoma. Arch Surg 2000; 135: Roozendaal GK, de Vries JD, van Poll D, et al. Sentinel nodes outside lymph node basin in patients with primary cutaneous melanoma. Br J Surg 2001; 88: Sumner WE, Ross MI, Mansfield PF, et al. Implications of lymphatic drainage to unusual sentinel nodes sites in patients with primary cutaneous melanoma. Cancer 2002; 95: McMasters KM, Chao C, Wong SL, et al.; Sunbelt Melanoma Trial Group. Interval sentinel lymph nodes in melanoma. Arch Surg 2002; 137: ; discussion, Weissleder H, Weissleder R. Lymphedema: evaluation of qualitative and quantitative lymphoscintigraphy in 238 patients. Radiology 1988; 167: Mortimer PS. Managing lymphedema. Clin Dermatol 1995; 13: Ely JW, Osheroff JA, Chambliss ML, Ebell MH. Approach to leg edema of unclear etiology. J Am Board Fam Med 2006; 19: Tiwari A, Cheng K, Button M, Myint F, Hamilton G. Differential diagnosis, investigation, and current treatment of lower limb lymphedema. Arch Surg 2003; 138: Altman DG. Practical statistics for medical research. London, UK: Chapman and Hall, Browse NL, Burnand K, Mortimer PS. The normal lymphographic appearances of the lower limb and pelvis. In: Kinmonth JB, ed. The lymphatics. London, UK: Edward Arnold, 1982: Hatta N, Morita R, Yamada M, Takehara K, Ichiyanagi K, Yokoyama K. Implications of popliteal node detected by sentinel lymph node biopsy. Dermatol Surg 2005; 31: Thompson JF, Hunt JA, Culjak G, Uren RF, Howman-Giles R, Harman CR. Popliteal lymph node metastasis from primary cutaneous melanoma. Eur J Surg Oncol 2000; 26: Szuba A, Shin WS, Strauss HW, Rockson S. The third circulation: radionuclide lymphoscintigraphy in the evaluation of lymphedema. J Nucl Med 2003; 44: Bräutigam P, Földi E, Schaiper I, Krause T, Vanscheidt W, Moser E. Analysis of lymphatic drainage in various forms of leg edema using two compartment lymphoscintigraphy. Lymphology 1998; 31: Burnand KM, Glass DM, Mortimer PS, Peters AM. Lymphatic dysfunction in the apparently clinically normal contralateral limbs of patients with unilateral lower limb swelling. Clin Nucl Med (in press) 20. Schunemann H, Willich N. Lymphoedema of the arm after primary treatment of breast cancer. Anticancer Res 1998; 18: Stanton AW, Modi S, Bennett Britton TM, et al. Lymphatic drainage in the muscle and subcutis of the arm after breast cancer treatment. Breast Cancer Res Treat 2009; 117: Major Criteria 1. Lymph rerouting through the skin, so-called dermal backflow 2. No visualization of lymph vessels 3. No ilioinguinal nodes visible on whole-body imaging at 45 minutes after tracer injection (delay) 4. Significantly reduced uptake in the ilioinguinal nodes (quantification < 5% at 180 minutes after tracer injection) a 5. Asymmetry of uptake, defined as less than half the amount in the contralateral ilioinguinal region a, between ilioinguinal node regions of interest on dedicated views at 180 minutes after tracer injection 6. Reduced number of ilioinguinal nodes visualized (i.e., < 2 at all times) Minor Criteria 1. Collateral lymph vessels ( 3) visualized 2. Rapid lymph transit: ilioinguinal node activity present within 5 minutes on whole-body images 3. Extravasation of tracer or dilatation of vessels identified as excessive pooling of activity or lymph lakes projected over the course of a lymphatic vessel 4. Asymmetry of uptake, defined as less than half the amount in the contralateral ilioinguinal region a, between ilioinguinal nodal activity in regions of interest at 60 minutes after tracer injection a Only in those patients with quantification data AJR:197, December 2011