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Calderwood et al. Plast Aesthet Res 2021;8:40 https://dx.doi.org/10.20517/2347-9264.2021.14 Page 7 of 14

Veins
In contrast to lymphatic vessels, veins appear straighter, smooth-walled, have focal areas of bulging from the
valves, and have lower signal intensity due to contrast washout-out from a faster flow. However, their
diameter can be similar to that of affected lymphatic vessels [3,7,18,23,24,26] . The enhancement kinetics of
lymphatic vessels and veins differs throughout dynamic contrast studies, with lymphatics becoming more
[2]
enhanced proximally over time and venous enhancement decreasing over time . Performing an MR
venogram and comparing it to the MRL can be helpful in distinguishing the veins.

Lymphatic vessel diameter
[18]
Both Mazzei et al. and Baz et al. claim that lymphatic vessel diameter can be useful in assisting
[1]
interpretation. However, lymph vessels dilation is only seen in 20% of lymphoedematous limbs, and both
authors agree that this is not a reliable feature for identifying affected lymphatic vessels . Vessel dilation in
[13]
the lower limb is defined by White et al. as > 3 mm below the knee and > 5 mm above the knee.
[7]
Bae et al. found the mean diameter of upper limb lymphatic vessels to be 1.98 ± 0.30 mm in healthy
[24]
individuals and 3.06 ± 0.78 mm in individuals affected with lymphoedema, with the difference being
statistically significant. Other reported diameter ranges in lymphoedematous limbs were 0.5-10 mm in
lower limbs and 0.5-5 mm in upper limbs [4,27,29] . Lu et al. found a statistically significant discrepancy in the
[14]
diameter of affected lower limb lymphatic vessels between contrast and non-contrast MRL, with the mean
vessel diameter measuring 3.41 ± 1.05 mm on contrast-enhanced MRL and 4.28 ± 1.53 mm on non-contrast
MRL. They hypothesized that this was due to the high endolymphatic pressure within the vessels that affect
the contrast uptake.

Dermal backflow
Dermal backflow is the dispersion of contrast into the dermal lymphatics or surrounding soft tissue,
suggesting obstruction of the lymphatic vessel, and identifies areas of high intralymphatic pressure and
excess lymphatic fluid [2,18,23] . It typically appears around 20 min after contrast injection and becomes more
prominent over time . Dermal backflow appears as an irregular, patchy, high signal intensity area, and the
[7]
reported prevalence is similar across multiple papers; 46.7% of patients with primary and secondary
lymphoedema, 53.84% of patients with primary lower limb lymphoedema, 63% of patients with secondary
lower limb oedema, and 52% of patients with oncology-related lower limb lymphoedema [3,16,18,23] .

Honeycombing
A honeycomb appearance (honeycombing) is the term used to describe the infiltration of lymph fluid into
subcutaneous fat or soft tissue, which is best appreciated on non-contrast heavily T2-weighted sequences
but can also be identified on contrast-enhanced MRL [7,14,17,21] . It has also been hypothesized that it could be
due to the opacification of multiple tiny peripheral lymphatic vessels associated with lymphatic backflow .
[14]
Honeycombing appears as a trabecular structure with enlarged fat pockets surrounded by lines of fluid or
fibrous tissue, and is characteristics of lymphoedema differentiating it from venous oedema, lipoedema, and
morbid obesity by demonstrating a combination of both fat deposition with fluid accumulation [8,19-21] . Two
studies independently found honeycombing to be present in 47% of subjects with known lymphoedema [3,14] .

Lymph nodes
MRL can be used to characterise the size, border, architecture, fluid transport, and the number of lymph
nodes, yet the appearance of lymph nodes on MRL is markedly variable due to the varying pathologies .
[34]
Secondary lymphoedema caused by surgery and/or radiation shows smaller and fewer lymph nodes in the
affected limb, whereas lymphoedema caused by lymph node metastasis has been found to demonstrate
enlarged lymph nodes [25,31] . Homogenous signal loss in the lymph nodes can be due to either complete
fibrosis of the nodes or, by contrast, not reaching the nodes because of stagnant flow upstream in the pre-