Surgical anatomy of the lingual lymph nodes: systematic literature analysis and proposition for topographic classification

Metastatic involvement of the lingual lymph nodes (LLNs) in oral cavity squamous cell cancer (SCC) has recently been proven to significantly reduce locoregional control and survival. Despite recent refinements in the detection of these lesions, the understanding of the LLN topographic anatomy among clinicians is limited. A proposition of a topographic division on LLN based on a comprehensive literature search and synthesis may be helpful in this condition. A literature search and election based on contemporary PRISMA guidelines was performed for sources on LLN anatomy with special attention on their subdivision. Four topographic LLN subgroups were defined: median—between genioglossal and geniohyoid muscles; intermediate parahyoid—medial to the hyoglossal muscle, at the greater cornu of the hyoid bone; lateral sublingual (paraglandular) LLNs—at the sublingual salivary gland; lateral submandibular (paraglandular) LLNs –lateral to the hyoglossal muscle, at the deep surface of the submandibular salivary gland. The development and implementation of a unified anatomical topographic classification of LLN subgroups may be among the important conditions for improving the detection and treatment of LLN lesions.


Introduction
The topic of the role of LLNs in the spread of oral tongue and floor of the mouth SCC has recently attracted the attention of clinical researchers. Modern investigation of LLN metastatic involvement started from a paper by Ozeki et al. which was followed by several reports in Japanese literature [1][2][3][4]. The results of the latest large prospective and retrospective clinical trials strongly suggest the significant negative prognostic value of these lesions in patients suffering from oral SCC [5][6][7]. Unfortunately, despite certain refinements in clinical and imaging recognition of LLN metastasis, details of their surgical anatomy are somewhat limited, and no unified topographic classification has been elaborated yet. This in turn may jeopardize the accuracy of the reported observations and results.
The purpose of this study was to perform a comprehensive search and analysis of the literature sources on the anatomy of LLNs and to determine a topographic-anatomic classification of different LLN subgroups.

Materials and methods
The literature search and analysis were conducted in accordance with the PRISMA guidelines [8]. Varying combinations of key word searches were undertaken in the PubMed, Google Scholar, J-stage and Archive.org databases. An additional search for Russian language sources was performed in the electronic catalog of the Russian State Central Medical Library-rusmed.rucml.ru (RSCML). After the primary investigation, the titles and abstracts of the selected sources were systematically screened. Those that possessed interest were addressed for further full-text evaluation (Fig. 1). Reference lists of the reviewed sources were subjected to additional investigation.
The following exclusion criteria for the scientific papers were used: studies, observations, reviews devoted to the anatomic region but with no information on the specific local anatomy or tumorous involvement of the LLNs. Sources that reported on radiotherapy and/or chemotherapy of the tongue and mouth floor subunits were also excluded.

Results
The numbers of sources and the process of their acquisition are illustrated in Fig. 1 and Table 1. The performed search resulted in 65 eligible studies for inclusion in a qualitative review and synthesis. The full text sources in English, German, Japanese, Russian and French tongues dated from 1868 to 2021. According to the explored databases, these sources were distributed in the following manner: PubMed-15; Google Scholar-5; J-Stage-10; Archive. org-23; RSCML-12 sources.
The literary sources on LLN anatomy we divided according to their data timeline into three sequential chronological periods (Fig. 2). The first period dates from 1868 to 1943 and in majority consists of fundamental works on human anatomy (Table 2a) [9,10]. The second period starts from observations in dissertational works of the late 1940s-early 1950s and lasts until the late 1980s [11,12]. This period is comprised of two types of sources: anatomic-topographic cadaveric studies with nonsystematic but sometimes detailed descriptions of LLNs and anatomy textbooks with information gained in large from the works of the first period (Table 2b). The third period, which lasted until now, started in 1985 with a paper by Ozeki et al. [4,13]. It is characterized by the gradual accumulation of clinical experience on LLN metastasis, the demonstration of a significant negative influence of these lesions on survival prognosis, and (what is more important to the present study) attempts to clarify LLN surgical anatomy (Table 2c).

Historical outline
The first chronological period starts with Henle's "Handbuch der Gefässlehre des Menschen", which in our knowledge is the earliest anatomic description of LLNs [14]. The most essential work of this period is H. Küttner's treatise "On lymphatics and lymph glands of the tongue with relation to the spread of carcinoma of the tongue" where the author gives an analysis of the available statistics. In a discussion on the clinical significance of LLNs, Küttner gives reference to Wölfler's report, which in our knowledge is the earliest academic mention of LLN metastasis in a patient with tongue cancer [15,16]. We see it necessary to bring a complete citation of this clinical observation.
Cadaveric studies described LLNs as inconstant regional lymph nodes of the tongue [12,22]. Mashkov (1968) found their incidence was 8.6% and included them in the regional draining lymph node group of the tongue [23]. Feind (1972) provided valuable references on LLN's position in the lymphatic drainage path flow and noted their potential role in tongue and mouth floor cancer metastatic spread [24]. Shelomentsev et al. (1974) studied the intraorganic lymphatics of the tongue and advocated wide dissection along the lingual artery and vein in conjunction with glossectomy [25]. Ozeki et al. (1985) reported a comprehensive observation of three different clinical cases of patients suffering from LLN lesions [4]. This was followed by several case reports in Japanese literature [26]. Dutton et al. (2002) speculated on the question of whether dissection of the LLN-bearing tissue performed in combination with glossectomy would improve local control in this group of patients [27]. Ando et al. (2009) described the clinical characteristics of metastases to the para-hyoid LLNs, which lie at the greater horn of the hyoid bone along lingual artery [28]. Ananian et al. (2015) identified LLNs in 23.8% cadavers [29]. Suzuki et al. (2016) classified LLNs into the following subgroups: median, anterior lateral (in the proximity of the sublingual gland), para-hyoid and posterior lateral (outside the lateral sublingual space-at the inner surface of the submandibular gland). This group was avoided by most previous authors [30].
The results of several studies confirm a pronounced negative impact on overall survival and recurrence-free survival with up to an eightfold decrease in prognosis [5][6][7]31]. As LLN lesions are often overlooked, it was postulated that every tongue and mouth floor cancer patient should be investigated for LLN existence and possible metastatic involvement by palpation, imaging or special dye tracing techniques preoperatively, intraoperatively and postoperatively [26,28,32,33]. The perception of LLNs as a clinically irrelevant issue or a rare finding must be abandoned. Special attention of clinicians should be focused on LLN in patients with 1 3 tongue and mouth floor cancer. This in turn requires the development of a unified nomenclature and a coordinated topographic classification.
Another common error is caused by the term "nodules", which was often used to refer to LLNs in the literature (especially in the second chronological period) [22-24, 38, 39]. According to our observations in English literature, the term "nodule" was first applied to LLN in a translated work by French anatomists [19]. In this tutorial authors discuss a paper by Stähr (1899) and an explanation of a German term is given: "Schaltdrüsen are the small nodules of interrupted glands whose presence is inconstant, number variable, and which are always unaffected by injections" [19,40]. This intermix could lead to some confusion between the two terms. The term "nodule" in further publications was closely linked with the lymphoid tissue ("die Lymphknötchen"-"noduli lymphatici") which form follicles in the mucous membranes-mucosa-associated lymphoid tissue (MALT) [41,42]. "Schaltdrüsen" was later used by a few German authors [15,18,20]. Bartels states on LLNs that he "halte sie für Schaltdrüsen in dem Sinne" (in a sense). Hence, this describes the position of the LLN, preceding the regional lymphatic basin [18]. Such an approach could later have been adopted by Feind (1972), who uses terms as "interrupting nodules" and "intercalated node" to point out their position in the regional lymphatic pathway, their small size, and anatomic inconsistency [24]. In our opinion, the closest modern term widely used in Japanese literature for LLN would be the "in-transit" lymph node [32,40,[43][44][45].

Topographical subgroups
LLNs between genioglossal and geniohyoid muscles. Located between the inner surfaces of the genioglossal and geniohyoid muscles within the median fascial space of the sublingual region. Küttner gave descriptions of "glands inside tongue musculature between the two mm. genioglossi". Poirier and Cuneo illustrated "ganglions intra-linguaux-intralingual node" within the tongue musculature [19]. Later, Most and Bartels referred to this group as anterior/median LLNs [18,20]. Albrecht (1925) reported the existence of an inconstant LLN between genioglossal muscles [46]. Rouviere (1932) and Nekrasov (1938) describe these under the term median LLNs [47,48]. Katayama studied embryos and reported an incidence of 15.1% [10]. Mashkov (1968) reported an incidence of 8.6% [23]. Ananian et al. did not observe median LLNs in their cadaveric study. Clinical experience with rare lesions of median LLNs suggests a negative locoregional control prognosis, as their location assumes bilateral tumor spread [49]. Eguchi et al. (2019) explored median LLN anatomy and described their location in the median sublingual space on each side of the lingual septum in a sagittal position of three-fourths of the distance from the mental spine [50].
Taking into account the abovementioned facts and topographical location of this LLN subgroup especially, that they do not have a contralateral pair (placed in the median sublingual space), the Latin term "medianus"-median should be considered as the most accurate. This designation is used in modern publications [27,51].  McClellan [67] Small LLNs are located along the lingual vein on the lymphatic route from the tongue mucosa to the deep jugular nodes 1987 Küttner [15] "Small glandule. linguales and those glands inside the tongue musculature between two genioglossal muscles" were described among regional draining lymph nodes of the tongue 1902 Gage [68] Inconstant LLNs which may be found on the ventral lymphatic pathway of the tongue, before it reaches the carotid nodal group 1903 Delamere et al. [19] Lateral LLNs are "paravisceral nodes" of the tongue and are located: close to the sublingual or deep to the submandibular glands, anywhere within the triangle formed by the anterior and posterior bellies of the digastric muscle 1905 Ellis [69] Few small LLNs may be found on the outer surface of the hyoglossus muscle. These transfer lymph flow to the upper deep jugular nodes 1906 Most [20] Inconstant anterior/median (between the two genioglossus muscles) and lateral (adjacent to the lingual artery and to the sublingual gland) subgroups of the LLNs 1909 Bartels [18] LLNs are regional lymph nodes of the tongue and are subdivided on anterior and lateral LLNs 1911 Rauber [70] LLN are located lateral to the root of the tongue 1918 Robinson [71] LLNs are located on the lateral surfaces of the genioglossal and hyoglossal muscle in the pathway leading to the upper deep jugular nodes 1918 Merkel [61] LLNs may be found in the lymphatic pathway of the tongue to the both sides of hyoglossal muscles. Pointed that they may have a great value 1922 Millard [72] Inconstant LLNs are positioned close to the sublingual gland 1925 Albrecht [46] Inconstant in-transit LLN, between genioglossal muscles. Lymph flow may be directed through these nodes to the contralateral side 1928 Sicher and Tandler [73] Rarely in single specimens deep LLNs may be found on the hyoglossal muscle. Special attention must be paid to their presence in case of nodal excision in tongue carcinoma 1936 Vorobiev and Yasvoin [59] Depicted LLN according to Rouviere-lying in the lymphatic pathway which runs in between the deep surface of the submandibular gland and the hyoglossus muscle 1938 Nekrasov [21] Two times observed lateral LLN during anatomic dissections and dye injections. Located on the XII nerve at the posterior digastric belly, these were termed "descending lateral LLNs". They were described as a transfer spot of the lymph drainage towards carotid lymph nodes 1938 Padgett [74] Between the genioglossal and above the mylohyoid muscles 1-2 LLNs are found and rarely may be palpated 1938 Rouviere [17] Subgrouped LLNs into median and lateral. Illustrated lymphatic pathways along the superficial and deep surfaces of the hyoglossal muscle towards superior jugular group Katayama [10] In a study of embryos found the incidence of median LLNs-15.1%, and lateral LLNs-30.2% b Second chronological period-anatomic data 1949 Semeina [12] Described rare findings of in-transit LLNs situated on the routes of lymph flow from the central and lateral surfaces of the tongue 1959 Kurbskaya [22] Inconstant small LLNs lying on the routes of main tongue efferent lymphatics. Central LLNs lie on the medial aspects of genioglossal muscles. Lateral LLNs reside on the outer surfaces of genioglossal and hyoglossal muscles along lingual vessels 1963 Aizenshtein and Khudaiberdiev [54] LLN are very small in size and consistency, are divided into anterior median, between the genioglossal muscles and lateral which are found along the arteria lingualis or near the sublingual gland. Named LLNs among regional draining nodes of the tongue. Mentioned lateral LLN at the deeper surface of the submandibular gland 1964 Zolotko [75] Median LLN may be observed in the central fascial space of the mouth floor 1965 Waldeyer [76] LLNs are rare, they are located around genioglossal muscles 1967 Andrushin and Virenkov [77] Small inconstant LLNs are located on the lateral surfaces of the geniogolossal and hyoglossal muscles 1968 Temirov [39] Documented one lateral LLN lying in close relation to the sublingual gland's parenchyma and draining the gland 1968 Mashkov [23] LLNs observed within tongue musculature in 8.6% of 104 cadavers. Outlined LLNs among regional for the tongue 1971 Edwards and Gaughran [78] LLNs lie between the hyoglossus and genioglossus muscles. They are interposed in the course of the lymph vessels which drain the lymph from the floor of the mouth to the deep cervical lymph nodes 1972 Feind [24] Classic tutorial with valuable data on LLNs. Contains some controversial standings and old-fashioned terminology. Classified LLNs among regional groups of the head and neck region. In another section the authors doubted if these should be put in the classification. Described a rare draining pathway of the surfaces of the tongue to pass a "sublingual intercalated nodule" before reaching a submental node. Summarized that "the floor of the mouth and the sublingual salivary gland drain into the intercalated sublingual nodule, the preglandular node of the submandibular group, and the subdigastric nodes of the internal jugular chain 1982 Langman and Woerdeman [79] Depicted single small LLN lateral to the root of the tongue 1985 Rouviere and Delmas [11] On the marginal routes of tongue lymphatics, which pass through the sublingual gland in-transit LLNs may be found c Third chronological period-anatomic data 1985 Ozeki et al. [4] First modern article which described LLN's metastatic lesions 1987 Som [80] Author noted that perhaps LLNs should not be strictly distinguished as lymph nodes, but rather as small lymph nodules located along the lymphatic vessels of the tongue and sublingual salivary glands 1991 Richter and Feyerabend [81] Illustrated LLNs on the lower lateral surfaces of the tongue Feneis [82] LLNs are located on m. hyoglossus, drain lymph from the lower tongue aspects 1998 DiNardo [47] "A sixth group of submandibular nodes seldom mentioned, but found to be important in the author's experience, shall be termed the deep submandibular nodes. Although absent from most anatomic references, these nodes have vaguely been described as existing on the deep surface of the submandibular gland The author has found these nodes to be small and inconsistently present. They are located anywhere along the undersurface of the submandibular gland but superficial to the mylohyoid muscle or posterior aspect of the hyoglossus muscle. They may be found as far superior as the attachment of the mylohyoid muscle to the mandible" 2001 Hiatt and Gartner [83] Inconstant, no more than 3 LLNs lie on the superficial surface of the hyoglossal muscle 2006 Shirochenko et al. [84] Median fascial space of the floor of the mouth sometimes contains 1-2 LLNs 2007 Uflacker [85] Named LLNs among additional lymph node groups of the upper aerodigestive tract 2007 Werning [86] LLNs Ando et al. [28,57] In detail described the location of metastatic para-hyoid lingual lymph nodes at the greater cornu of the hyoid bone 2010 Hoshina et al. [32] Reported several cases of LLNs metastases beyond sublingual fascial spaces. These LLNs are covered by the deep surface of the submandibular gland lateral to the outer surface of the hyoglossal muscle 2012 Shalina and Petrova [88] LLNs are located lateral to the root of the tongue along lingual vessels 2015 Ananian et al. [29] Observed lateral (parahyoid and sublingual paraglandular) LLNs in 23.8% of the studied 21 cadavers 2016 Suzuki et al. [30] Classified LLNs into following subgroups: median, anterior lateral (in the proximity of sublingual gland), posterior lateral (outside the sublingual space-at the inner surface of the submandibular gland) and parahyoid 2019 Eguchi et al. [50] Explored median LLNs, reported their location in the median mouth floor space on each side of the lingual septum in a sagittal position of three-fourth of the distance from the mental spine 2019 Eguchi et al. [48] Reported that lateral LLNs (especially those at the deep aspect of the submandibular gland) are separated from the contents of the submandibular space by the deep lamina of the cervical fascia 2020 Obukhova [89] LLNs are inconstant nodes located on the lateral surface of the hyoglossal muscle and drain lymph from the tongue mucosa 2020 Abou-Foul [51] Summarized data on the incidence of lateral and median LLNs to be 24-30% and 0-15.1%, respectively.

Suggested the term "intermediate" for the parahyoid subgroup
LLNs at the greater horn of the hyoid bone along a. lingualis. Located medially to the hyoglossal muscle along the route of the lingual artery in the intermediate sublingual space. Wolfler (1881), Sachs (1893), and Roediger (1901) gave concise descriptions of a lymph node adjacent to the wall of the lingual artery and metastatic lymph nodes that were situated at the horn of the hyoid bone [16,52,53].
A Soviet textbook reported that lateral LLNs may be found along the lingual artery course [54]. Close connections of the lingual lymphatic vessels with the sublingual gland passing through its parenchyma and draining the gland itself were documented. The main extraorganic efferent lymphatic trunks were found to be located along the branches of the lingual artery and vein. To achieve better local control, the authors advocated wide dissection along the lingual artery system with sublingual gland removal in combination with glossectomy [55,56]. Ando et al. provided accurate clinical characteristics of "lateral para-hyoid" LLNs and observed their metastatic involvement in 6.3% of 248 patients with T1-2 tongue SCC [28,57]. Ananian et al. reported an anatomic incidence of 19% in their 21 cadaveric specimens [29]. Suzuki et al. (2016Suzuki et al. ( , 2021 refer to these as para-hyoid LLNs [30,58].
LLNs in the proximity to the sublingual salivary gland. These LLNs are located close to the sublingual gland on the upper surface of the mylohyoid muscles within loose fatty tissue of the lateral sublingual space. This space is bordered anterior-laterally by the inner surface of the mandible and harbors blood vessels, the sublingual gland, the submandibular duct with the deep portion of the submandibular gland, and the branching hypoglossal, mylohyoid and lingual nerves. Most terms these lateral LLNs and indicates that they may be found near the sublingual gland [20]. Katayama reported an incidence of lateral LLN of 30.2% [10]. Feind states that LLNs are a part of the tongue and mouth floor drainage pathway, though delineates their rare consistency [24]. Suzuki et al.'s classification terms these LLNs as anterior lateral [30]. Ananian et al. termed them lateral paraglandular LLNs, which was formed by analogy with the subdivision of the submandibular nodes [29].
LLNs behind the deep surface of the submandibular salivary gland. It is intriguing that despite available data in anatomic sources that LLNs may be found on the lateral surface of the hyoglossal muscles, these LLNs received little attention as a separate subgroup [9,19,22,38,45,59]. Nekrasov (1938) left meticulous reports of two observations of LLNs that were located on the hypoglossal nerve at the posterior digastric belly [21]. The author described these LLNs as a transfer spot of lymph drainage towards the carotid triangle and termed them "descending lateral LLNs", as they descend from their usual position in the sublingual area. DiNardo (1998) provides a valuable reference [47] ( Table 2c) [30]. The same authors (2019, 2021) reported a case of metastatic involvement of the lateral LLN situated outside the sublingual area and covered by the deep surface of the submandibular gland. It was noted that these deeply situated LLNs lie in the course of the hypoglossal nerve and are topographically separated from the contents of the submandibular fascial space by the deep lamina of deep cervical fascia [48,58].

The deep submandibular (intracapsular, paramandibular) lymph node
Feind and later DiNardo both gave scarce data on nodes that lie behind the submandibular gland's medial surface covered in the depth of the submandibular gland [24,47]. After initial report by von Brunns, Bartels published a rare observation of a "paramandibular" lymph node [14,60]. Merkel notes that submandibular nodes may be located deep and sometimes covered by the gland's capsule [61]. According to Blair these nodes should be classified within the regional submandibular group [62]. Nekrasov included it in his regional node classification [21] (Table 3). Year of publication Authors Data 2020 Hoffman and Eisenberg [90] Lateral LLN-are located on the outer surface of the genioglossus muscle; Median LLN-are located in the median septum; Deep Lingual node-located at the root of the lingual artery, in the parahyoid region, deep to hyoglossus muscle in the postero-basal midline 2021 Suzuki and Eguchi et al. [58] Reported a case of metastatic involvement of the lateral LLN situated outside the sublingual area covered by the deep surface of the submandibular gland. Authors noted that these deeply situated LLNs are anatomically separated from the contents of the submandibular fascial space by a thin lamina of deep cervical fascia 1 3 The clinical meaning of this lymph node refers to a debate as to whether the submandibular gland can harbor metastasis of oral SCC, and may be spared during neck dissection in patients with a low risk of neck metastasis. Significant scientific material accumulated to date testifies to a very low frequency of finding lymph nodes in the parenchyma of the submandibular salivary gland and even lower rates of lymphogenic lesions of the gland in oral cancer patients [63].
Terminology of this lymph node is beyond the scope of the current study, although there are three different possible terms that were already used in the literature. The deep submandibular, intracapsular submandibular or modernized from Bartels' parasubmandibular node (the author and his teacher Bardeleben disagreed with the BNA term glandula submaxillaris and instead used term glandula mandibularis; hence, the paramandibular node reflects its affiliation with the gland) [64,65].
In the narrative of the present study, it would be rational to indicate that this lymph node, although may exist as a very rare anatomical variation it should not be attributed to LLNs.

LLN subgroup classification
The performed analysis, data synthesis and topographical subdivision of LLNs were based on the explored anatomical data and on regulations of International Anatomical Terminology, in particular, that all organs that are tightly connected with each other topographically should have similar titles [66]. Existing LLN terminology was reviewed, and analogical subdivisions of other regional groups of the head and neck were taken into account. General terms such as anterior/posterior and anterior lateral/posterior lateral were put aside from the synthesis, as their utilization already caused some misunderstanding among authors.
Among all the LLN subgroups it is the median subgroup, that does not cause terminological disagreements. The term totally reflects their relative position-a parameter of topographic subdivision.
Ando et al. initially named LLNs at the greater cornu of the hyoid bone "lateral para-hyoid" [28]. Suzuki et al. termed these "para-hyoid" without the nomina generalia "lateral" [30]. Abou-Foul, in his systematic review, recalls these LLNs as intermediate para-hyoid LLNs. As they are Table 3 Deep submandibular/intracapsular/paramandibular nodes-anatomic data Year of publication Author/title Essentials 1903 Von Brunn [60] Examined 61 submandibular glands, which were sectioned in 2-3 mm thick slices, unstained. In two glands he could observe lymph nodes which were embedded into the capsule and situated in a groove formed by facial artery on the deep surface of the gland 1907 Bartels [14] Described a rare observation of a "paramandibular" lymph node. It was revealed after dye injection at anterior part of the oral tongue and had an unusual location: deeper to the posterior median margin of the submandibular gland, was included in the gland's capsule and at the same time separated from its parenchyma by a blood vessel 1918 Merkel [61] Mentioned that submandibular lymph nodes can lay in the capsule of submandibular gland and named them "Lymphoglandula paramandibularis" 1923 Corning [91] Reported that among submandibular lymph nodes deep seated nodes may be found, which are covered by the submandibular gland. Author notes that to achieve final resection of the submandibular lymph nodes it is necessary to keep attention to possible existence of these deep submandibular nodes 1929 Blair [62] Reported an original observation of a lymph node covered by capsule of the submandibular gland. According to author's opinion, these nodes should be classified within the regional submandibular group 1932, 1938 Rouviere [17,92] Names intracapsular lymph nodes among the submandibular regional group 1938 Nekrasov [21] In one cadaver he observed: a tiny lymph node on lateral wall of the facial artery near the origin of the ascending palatal artery, at this point the submandibular gland surrounded the node and vessel itself. This node received blood supply from fine branches of the ascending palatal artery. Grouped these among submandibular nodes 1972 Feind [24] Mentioned "intracapsular submandibular nodes" and described their embryological development: "These nodes probably reach this position in development of the fetus by the same mechanism seen in the parotid group. The submandibular salivary gland migrates back from the floor of the mouth as paired primordial cords, representing the main duct. It continues back to the angle to the angle of the mandible along the floor of the mouth, then turns down and ventrally sprouts out into its lobulations containing the acini. The lymphatics are present and may become engulfed by this process, but this is a very rare happening experience" 1998 DiNardo [47] Reported contradictive data on these lymph nodes. Informed that in rare cases "intracapsular submandibular lymph nodes" may play role in regional spread of tongue cancer. Did not observe these lymph nodes in his anatomic material 1 3 located within the intermediate fascial space of the sublingual region, the term "intermediate-intermedius" should replace a less accurate "lateral" titling, and the full term would be "intermediate para-hyoid LLN" [51]. For lateral LLNs, two locations should be addressed: LLNs in the proximity to the sublingual gland and LLNs at the deep aspect of the submandibular gland. The topographic designation "lateral" is applicable and fully legitimate for both (especially keeping in mind the opinion that the latter nodes are "descendent" lateral LLNs). The clarifying term "paraglandular" reflects the node's topographical relation to the sublingual gland, and is formed in a similar manner to the submandibular nodes division-as retro/preglandular submandibular nodes in Feind's classification [24,29]. We observed two locations, both of which are related to a salivary gland: the sublingual and the submandibular glands.
Thus, the titles are to be "lateral sublingual paraglandular LLNs" and "lateral submandibular paraglandular LLNs". To avoid vocabulary piling out, the specifying "paraglandular" part may be omitted (Table 4).
On the other hand, considering the fact that the LLNs behind the submandibular gland are covered by the deep lamina of the cervical fascia [48] and in morphologic stratification are separated from the fascial space of the submandibular gland, the description "descending lateral LLNs" as used by Nekrasov may be an elegant alternative (Fig. 3).
In common clinical conditions, the presented classification and nomenclature may be useful for raising awareness of the LLN lesions and their localization. As each subgroup received its title and the assigned names of the subgroups reflect their topographical position this may increase the accuracy and somewhat simplify the reporting on LLNs.

Conclusion
The development and implementation of a unified anatomical topographic classification of the LLN subgroups, which would not cause difficulties and misunderstandings in use, may be among the important conditions for improving the detection and treatment of LLN lesions. Funding Personal monetary funds.

Data availability
The data used to support the conclusions of this study are included within the article.

Declarations
Conflict of interest There authors declare that there is no conflict of interest. In the lateral sublingual fascial space-in the proximity to the sublingual salivary gland Lateral submandibular (paraglandular) LLNs Outside the sublingual region-behind the inner surface of the submandibular salivary gland, in the deep layer of the submandibular triangle, lateral to m. hyoglossus Ethical approval Not applicable.

Consent to participate Not applicable.
Consent for publication Not applicable.