Currently, prediction models for lymphedema at home and abroad mostly predict the risk of lymphedema in cancer patients after surgery. Different models have been established based on clinical data, laboratory tests and imaging indicators to predict the risk of early secondary lymphedema in breast cancer or gynaecological cancer patients[3–8, 11, 12]. Xuan Tung Rinh[8] successfully developed a machine-learning model for predicting lymphedema using blood and treatment data and proposed that future research focus on predicting the stages of lymphedema. This study was based on previous research and proposed a PLEL model based on clinical and imaging data that can effectively distinguish between non-severe and severe PLEL, thereby improving the diagnostic performance of clinical models. Therefore, we constructed a nomogram prediction model that includes clinical features, imaging features, and lower limb oedema measurements. This non-invasive method can be used to evaluate the severity of PLE preoperatively, providing a reliable approach for the next treatment plan.
PLEL has two different progression directions, namely, from top to bottom and bottom to top, with the former being more common; the former is caused by the structural or functional insufficiency of peripheral superficial lymphatic vessels, leading to the leakage of lymphatic fluid along the diseased ducts, whereas the latter is caused by the structural or functional insufficiency of central lymphatic vessels or lymphatic trunks (such as the thoracic duct, cisterna chyli, lumbar and iliac lymphatic trunks), leading to the downwards reflux of lymphatic fluid, causing the lymphatic chyle to reflux to the lower limbs [13, 14]. The results of this study revealed that 96.4% of severe patients experienced complete lower limb involvement(Fig. 8), and this indicator is an independent risk factor for severe PLEL. It is speculated that severe patients may have both peripheral and central lymphatic vessel structural and functional deficiencies.
Previous studies, both domestic and international, as well as our research, have found that parallel line signs, grid signs, honeycomb signs, band signs, lymph lake signs, and crescent signs on MR images of patients with lymphedema are closely related to the severity of lymphedema[10, 15, 16]. The results of this study confirmed that these signs significantly differed in terms of imaging indicators between the two groups. This study revealed that the parallel line sign, crescent sign, and band sign thickness are independent risk factors for distinguishing non-severe and severe PLEL. The parallel line sign may be mild dilation of subcutaneous lymphatic capillaries and a small amount of lymphatic exudate, which accumulates and stimulates the proliferation of adipose tissue linearly. Some researchers believe that the parallel line sign is a characteristic manifestation of mild lymphedema[10], which is consistent with the results of our study. Aström KG et al.[15] suggested that subfascial effusion (i.e., the crescent sign in this study) can be used as an indicator to determine the severity of lymphedema. The crescent sign is a vicious cycle formed by the continuous leakage of subcutaneous lymphatic fluid and increased local inflammatory factors that damage lymphatic vessels in severe patients. The accumulated lymphatic fluid gradually spreads to the fascia and muscles. Cellina et al.[16] found that suprafascial effusion (i.e., the band sign in this study) can be used as an indicator to determine the clinical stage of lymphedema. This study revealed a statistically significant difference in the band sign between the two groups, which can be used as an indicator to determine the severity of lymphedema. However, band sign is not an independent risk factor for severe PLEL, and band sign thickness is an independent risk factor for severe PLEL. We speculate that the band sign thickness and the presence of the crescent sign are independent risk factors because of the different anatomical locations of fluid accumulation in each sign. Hauck G[17] confirmed the existence of a "low resistance pathway" for fluid transport from capillaries to lymphatic vessels along connective tissue fibres. The distribution of collagen and elastic fibres in the superficial fascia can guide lymphatic fluid to flow in the correct direction. Fascia is a dense connective tissue with a strong impedance that blocks fluid diffusion. If the superficial fascia changes, lymphatic drainage will be affected. The fluid accumulates on the superficial fascia and enters below the subfacia upon reaching certain levels, forming a crescent sign. The quantitative change in the band sign causes a qualitative change in the crescent sign, so the former measurement can more objectively reflect the severity of lymphedema.
In addition, we also included measurements of four components (skin, bone, fat and soft tissue) of the lower limbs. The total diameter, fat diameter, soft tissue diameter, total circumference, total area, fat area, soft tissue area, skin thickness, band sign thickness, and crescent sign thickness were closely related to the grade, and there was a statistically significant difference in the imaging indicators between the two groups. Fat area and fat diameter were independent risk factors for severe PLEL, which confirms that the disease does not involve bones or muscles. This result is similar to the findings of Liu et al.[18]. Thickened subcutaneous adipose tissue plays a major role in increasing limb volume in patients with primary lower limb lymphedema. This feature is also the primary difference between lymphedema and venous oedema. These findings also indicate that the lesions in the fat layer of lymphedema are the most important areas for determining the severity of lymphedema. Patients with primary lymphedema experience slow lymphatic flow due to congenital lymphangiodysplasia and functional decline [19]. The exudate of lymphatic fluid is usually confined to the surface membrane spaces of the skin and subcutaneous tissue without involving deeper muscles; this leads to a gradual increase in subcutaneous fat layer oedema. The lymphatic flow of patients with severe lymphedema is further slowed, stagnant in the subcutaneous fat layer, and stimulates fat production and deposition, leading to fibroblast activation and excessive growth of connective tissue. Enlarged adipose tissue and fibrous tissue accumulate around the subcutaneous soft tissue, leading to further swelling of the subcutaneous tissue in the limbs[20].
Deficiencies
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Staging reflects the pathological and physiological conditions of lymphedema and the process of disease occurrence and development. Grading also reflects the degree of swelling in the affected limbs of patients with lymphedema and is also the main basis for the clinical selection of surgical procedures. Therefore, this paper only discusses lymphedema grade.
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This paper only discusses the establishment of a nomogram prediction model for severe primary lower limb lymphedema preliminarily. Our further research will establish a three-class prediction model for mild, moderate, and severe lymphedema.
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This study focused on PLEL, which is rarer than secondary lymphedema. PLEL is a type of congenital disease and is less affected by factors than secondary lymphedema. Therefore, this study takes PLEL as the starting point, and subsequent studies will include patients with secondary lymphedema.
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In previous studies, we discussed surgical treatment for patients with primary lower limb lymphedema. In this study, we discussed only predictive models and did not address treatment.