兽研简要总结
犬下颌腺和舌下腺的实性病变较为罕见，临床上难以与其他颈部肿胀相区分。在本病例报告中，我们描述了一只11岁马尔济斯犬，体格检查和X线检查发现左侧颈部区域存在一个大型、边界清晰、坚硬的团块。手术切除受累唾液腺复合体后，在腺体复合体内取出一个心形实性凝结物。对取出物质的光谱成分分析表明，其含有大量富含蛋白质和脂肪（脂质）的有机成分，可能含有少量矿物质成分，而唾液腺结石通常被认为主要以矿物质为主。周围组织的显微镜检查证实腺体存在慢性炎症、萎缩和瘢痕形成（纤维化）。该犬术后恢复无并发症，术后两周完全愈合。未进行计算机断层扫描等更先进的影像学检查，此类检查本可有助于术前更精确定位病变。本病例表明，犬X线片上显示的唾液腺病变并非总是以矿物质为主，在颈部肿胀的诊断工作中应考虑唾液腺内富含蛋白质的团块，且手术切除受累腺体可获得良好的短期预后。
1. 引言
唾液腺和唾液腺导管疾病在犬和猫中总体不常见[1]。下颌腺位于舌面静脉和上颌静脉之间，即两静脉汇合形成颈外静脉处，并与舌下腺的单口部分融合，二者共享密切相关的导管系统——这一解剖关系解释了为何该复合体的唾液腺切除术通常涉及两个腺体的整块切除[1]。犬的唾液腺疾病包括唾液囊肿（唾液黏液囊肿）、唾液腺炎、唾液腺结石和肿瘤，其中黏液囊肿形成是最常报告的疾病，而唾液腺结石在该物种中被认为罕见[2,3]。
唾液腺结石最常描述于腮腺导管，而累及下颌—舌下腺—导管复合体者仅偶尔报道，通常为孤立病例报告[4,5,6,7]。其他非阻塞性腮腺导管疾病，如腮腺导管扩张，也已在犬中有所描述，进一步说明该物种的唾液腺导管病理主要集中于腮腺而非下颌—舌下复合体[8]。已报道的犬唾液腺结石通常由碳酸钙或磷酸钙组成，尽管非矿物性、富含蛋白质的结石也有记录[7]。在人类中，蛋白质组学和光谱学研究同样表明，相当一部分唾液腺结石以有机或蛋白质成分为主，矿物质沉积仅次之（如果有的话），这表明在没有成分分析的情况下不能假定实性唾液腺相关凝结物本质上是矿物性的[9]。
临床上，下颌—舌下复合体的唾液腺结石通常表现为下颌下或颈部肿胀，仅凭体格检查可能难以与唾液囊肿、脓肿、异物反应或肿瘤相区分[3,5]。平片X线检查可显示矿物不透性结石并支持临床怀疑，而确诊依赖于切除腺体和导管组织的组织病理学检查[4,6]。通过腹侧或侧方颈部入路对受累下颌腺和舌下腺行唾液腺切除术，仍是该腺体复合体唾液囊肿和唾液腺结石的标准治疗方法，文献报道长期预后总体良好[5,10,11]。
我们报告一例犬下颌—舌下唾液腺复合体相关的大型X线不透性凝结物，含有大量有机、富含蛋白质和脂质的成分，伴继发性唾液腺炎。该病变通过临床检查、细胞学和颈部X线检查发现，经腹侧入路手术切除，周围腺体组织行组织病理学检查，而凝结物本身通过傅里叶变换红外（FTIR）光谱法进行表征。在本报告中，“凝结物”一词用于指切除的病变，因为其大量有机成分使其区别于传统的以矿物质为主的唾液腺结石；“唾液腺结石”和“结石”指先前报道的唾液腺结石，“凝结物”用作涵盖两者的通用术语。
2. 病例介绍
2.1. 基本信息
一只11岁、未绝育（未去势）的雌性马尔济斯犬，体重5 kg，就诊于外科诊所。
2.2. 病史
主人报告称，约在就诊前3周抚摸犬只时偶然发现肿胀。因肿块在过去7天内明显增大，遂决定寻求兽医诊疗。主人未注意到食欲或行为变化，该犬此前未接受过针对此病的任何治疗。
2.3. 体格检查
就诊时，该犬警觉，体温正常（直肠温度38.5 °C），呼吸频率30次/分，心率110次/分。一般体格状况无异常，该犬食欲和饮水量维持正常。左侧颈部/腹外侧区域触诊可及一直径约2–3 cm的单侧无痛性肿物，质地不均——表面柔软、深部坚实。口腔及牙列检查未见异常，唾液腺管开口处未见变化。区域淋巴结（下颌/咽后）触诊大小正常。
2.4. 术前实验室检查结果
术前全血细胞计数和血清生化分析分别使用VetScan HM5血液分析仪（Abaxis，Union City，CA，USA）和BioSystems BA200分析仪（BioSystems，Barcelona，Spain）进行，结果总结于表1。血液学参考区间采用分析仪制造商提供的数值，生化参考区间采用《默克兽医手册》[12]的数值。注意到血红蛋白和MCH轻度升高，碱性磷酸酶显著升高，同时离子钙浓度轻度降低；其余参数均在参考区间内（表1）。
2.5. 心脏病学评估
麻醉前心脏病学评估，包括听诊、心电图和经胸超声心动图（Vetus 8，Mindray，Shenzhen，China），除呼吸性窦性心律不齐和游走性起搏点外未发现异常，两者均被视为犬的生理性变异，未发现全身麻醉的禁忌证。
2.6. 诊断影像学
使用Maxivet 400 DR数字兽医X线摄影系统（COMES ELECTRO S.r.l.，Cavaria con Premezzo，Italy）拍摄颈部和胸部X线片，包括右侧位和左侧位，以评估颈部肿物。胸部X线片作为麻醉前筛查的一部分拍摄，并用于评估可能的肺转移，因为肿瘤已被列入鉴别诊断。右侧位片（图1）显示胸廓骨骼结构无创伤性或退行性改变，膈肌影像学正常，气管走行迂曲但管径正常，心血管结构影像学表现正常；肺部无转移的影像学证据。在颅侧颈部区域可见一界限清晰、约卵圆形的阻射结构，大小约3.1 × 2.9 cm，在侧位片上与咽部区域重叠，可能偏侧化；由于患者保定困难（检查时患者焦虑），无法确定其确切位置；出于同样原因，未能获得有助于确定偏侧化的正交腹背位片。这些发现提示怀疑与实性阻射结构相关的唾液腺疾病，建议进行牙科和外科会诊。
2.7. 鉴别诊断
就诊当日、手术前一天对肿物柔软、波动性成分进行的细针抽吸获得了清亮浆液黏液性液体。抽吸液细胞学检查显示大量无定形黏液物质，混有大量泡沫状巨噬细胞、偶见非退行性中性粒细胞和数量不等的红细胞；抽吸液中未发现恶性肿瘤的细胞学特征。抽吸液的细菌学检查于采集当日送检，在“Ion Ionescu de la Brad”雅西生命科学大学兽医学院微生物学实验室进行，包括革兰染色涂片直接显微镜检查和血琼脂、麦康凯琼脂、脑心浸液和巧克力琼脂培养，36 °C孵育48小时；未获得细菌生长；切除组织未送细菌学培养。细胞学发现与唾液内容物一致，如黏液囊肿（唾液腺囊肿）中所见；然而，仅对肿物的液体成分进行了采样，这些发现不一定代表其实性成分。鉴于无痛性、缓慢进展的颈部肿胀伴质地不均、这些细胞学发现以及区域淋巴结正常，考虑了几种鉴别诊断。
唾液腺囊肿（唾液黏液囊肿）最初被考虑，是因为其质地柔软、有波动感，且抽吸液呈黏液性——颧腺唾液腺囊肿和位于咽壁的唾液腺囊肿（咽部唾液腺囊肿）同样有报道在犬表现为缓慢进展的无痛性肿胀[13,14]；然而，X线片上出现边界清晰、质地坚实的阻射性结构并非无并发症黏液囊肿的典型表现，而更提示为实性阻塞性团块伴继发性腺体受累。脓肿的可能性较小，尽管仅凭临床依据不能排除，因为肿块无痛、患畜在整个检查过程中无发热且呼吸正常，全血细胞计数也未显示明显的炎症性白细胞象。鉴于触诊到的坚实成分，也考虑异物反应，但无外伤、口腔/牙齿疾病或异物吞食史，且X线片上所见边界清楚、卵圆形的阻射性结构更提示为实性唾液腺相关团块而非异物，尽管仅凭阻射性不能确定其成分。考虑到患畜年龄，也考虑了肿瘤，但无区域淋巴结肿大、肿块在X线片上呈非浸润性且边界清晰、触诊无疼痛，使该鉴别诊断可能性较低；然而，由于细胞学仅采样了液体成分，在组织病理学检查前不能排除肿瘤。基于这些发现，下颌-舌下腺复合体的实性阻塞性团块伴继发性唾液腺炎被认为是最可能的初步诊断，需通过手术探查、组织病理学检查和成分分析予以确认。
2.8. 麻醉与镇痛方案
术前用药为美沙酮（Insistor，Richter Pharma AG，Wels，奥地利）静脉注射，剂量0.3 mg/kg（5 kg患畜总剂量1.5 mg）。使用阿法沙酮（Alfaxan，Jurox Pty Ltd.，Rutherford，NSW，澳大利亚）静脉注射至效应（总剂量3 mg/kg）诱导全身麻醉，并以异氟烷（IsoFlo，Zoetis Belgium SA，Louvain-la-Neuve，比利时；1–2%）在氧气中维持，使用配备一体化呼吸机的R650兽医麻醉机（RWD Life Science Co., Ltd.，深圳，中国）进行辅助（机械）通气；维持阶段静脉推注氯胺酮（Ketamidor，Richter Pharma AG，Wels，奥地利）2 mg/kg用于围手术期镇痛。额外镇痛通过在计划切口线多点局部浸润利多卡因（LidoBel 20 mg/mL，Bela-Pharm GmbH & Co. KG，Vechta，德国）提供，剂量4 mg/kg（总剂量20 mg；5 kg患畜1 mL）。术中液体治疗为平衡晶体液（林格氏液；Infomed Fluids SRL，布加勒斯特，罗马尼亚），使用输液泵（BeneFusion VP3 Vet，迈瑞，深圳，中国）以5 mL/kg/h的恒定速率给药，液体经血液及输液加温器（Eickemeyer，Tuttlingen，德国）加温。手术时长90分钟。术中使用多参数兽医监护仪（uMEC 10 Vet，迈瑞，深圳，中国）进行监测，包括心电图、心率、脉搏血氧饱和度（SpO2）、二氧化碳描记（呼气末CO2，EtCO2）、无创（示波法）血压、呼吸频率和体温。心率范围为90至120次/分，SpO2维持在96%至98%之间，EtCO2维持在大约40 mmHg，呼吸频率约25次/分，平均动脉压维持在大约70 mmHg，无低血压发作。诱导时体温38.5 °C，手术结束时38.1 °C；使用强制暖风保温系统（WMS-1501，AEOLUS International Pet Products，Irving，TX，美国）维持正常体温。
2.9. 手术技术
选择腹侧旁正中入路以暴露并切除受累的下颌-单口舌下唾液腺复合体。该入路可直接进入下颌腺和单口舌下腺，与外侧入路相比，在因唾液囊肿行唾液腺切除术的犬中，其复发风险较低，尽管伤口相关并发症可能更常见[15]。患者取仰卧位（图2A）。沿肿胀长轴作3-4 cm旁正中皮肤切口，距颈外静脉约10 mm。在舌面静脉与上颌静脉汇合形成颈外静脉处附近识别舌面静脉（图2B）。舌面静脉紧贴并部分粘连于下颌腺被膜；仔细游离并保持其完整性。下颌腺和单口舌下腺作为单一腺体复合体被暴露。识别面动脉的腺支并结扎（图3A）。继续分离直至识别下颌腺管和舌下腺管；将腺管从腺体复合体分离一小段距离，然后用3-0可吸收单丝缝线结扎并在靠近腺体处切断（图3B）。随后通过皮肤切口将腺体复合体整块移除，辅以轻柔牵拉皮肤边缘。其仍包裹于被膜内的大体外观见图4A。去除被膜后，从腺体复合体内取出一个心形、实性团块（图4B）；该团块位于腺体复合体内，未见于下颌腺管或舌下腺管腔内；其切面外观见图4C。切开后，团块被分为约2×1.5 cm的碎片，连同腺体组织一起送检组织病理学检查（第2.11节），剩余材料送检FTIR光谱分析（第2.12节）。手术部位用3-0可吸收单丝缝线分两层闭合：皮下组织采用连续缝合，皮肤采用简单间断缝合。
2.10. 围手术期和术后用药
术后抗炎和镇痛治疗包括美洛昔康（Melovem注射液，Dopharma Research B.V.，Raamsdonksveer，荷兰），术后立即皮下注射0.2 mg/kg，随后口服美洛昔康混悬液（Rheumocam，Chanelle Pharmaceuticals Manufacturing Ltd.，Loughrea，爱尔兰）0.1 mg/kg，每日一次，再持续4天。抗生素治疗包括阿莫西林-克拉维酸（Kesium，Ceva Santé Animale，Libourne，法国），口服12.5 mg/kg，每12小时一次，共5天。由于怀疑继发性唾液腺炎以及手术暴露了与口腔相通的导管系统，该治疗在细菌学结果可用之前（术前一天采集的抽吸物48小时培养仍在进行中）经验性开始，并作为短疗程完成。术后24小时更换手术敷料。
2.11. 大体和组织病理学检查
对切除的腺体复合体进行组织病理学检查，标本固定于10%福尔马林；检查了一张Masson三色染色切片，未进行常规苏木精-伊红（H&E）染色（图5）。团块碎片（约2×1.5 cm），白色，表面粗糙，质地坚硬，连同腺体组织一起送检但未切片；仅对腺体组织进行了组织学处理和检查，未进行矿物特异性染色（如von Kossa或茜素红）。周围组织符合残留唾液腺实质和/或排泄管，含有少量分泌型上皮细胞群，胞质呈泡沫状，细胞核位于中央，同时可见胞质嗜碱性、颗粒状的细胞，可能来源于混合性唾液腺泡。纤维结缔组织占主导，伴有大量新生血管，在某些区域呈现肉芽组织样外观（图5A）。还观察到混合性炎性浸润和出血区域（图5B），以及符合矿化的区域（图5C）。纤维间质内还可见脂肪组织浸润（图5A）。切除标本包括一个淋巴结，滤泡结构大部分保留，主要在皮质区轻度稀疏，显示含铁血黄素沉着和脂褐素沉着。组织病理学诊断为唾液腺萎缩、纤维化和唾液腺炎。
2.12. 团块的傅里叶变换红外（FTIR）光谱分析
切除的凝结物（第2.9节）的剩余材料被送至一家外部认证诊断实验室（Laboklin GmbH & Co. KG，德国巴特基辛根），通过傅里叶变换红外（FTIR）光谱法进行成分分析。该分析在该实验室经认证的结石分析范围内进行，该范围包括所有动物种类的唾液腺结石。如实验室报告所述，提交的材料包括九块表面粗糙的米色碎片，大小范围约为1×1 mm至22×22 mm。该材料在手术取出时为白色，到分析时已变为米色，可能是脱水的结果，脱水也可能使碎片尺寸缩小。使用自动谱库搜索软件Opus 8.5版将样品的FTIR光谱（图6）与实验室的参考光谱库进行比对；最接近的匹配为蛋白质参考光谱，报告的匹配质量为54.56。该值代表实验室谱库搜索软件生成的相似度指数，数值越高表示样品与参考光谱之间的一致性越接近；54.56这一数值低于用于尿石FTIR谱库鉴定的接受标准。接受标准因软件和实验室而异；在一份已发表的犬尿石分析方案中，0–1000量表上至少800的命中质量值被视为高置信度，700–800的值被视为初步结果[16]。实验室未报告所采用的量表或接受标准，但无论以0–100还是0–1000量表表示，54.56这一数值均低于这些标准。样品光谱和参考光谱均在3300–3000 cm⁻¹附近显示宽的酰胺A/B吸收带，并在1650 cm⁻¹和1550 cm⁻¹附近显示特征性的酰胺I和酰胺II带，与蛋白质性基质的肽骨架振动一致[17]。除酰胺带外，样品光谱还在约2920/2850、1740、1465和720 cm⁻¹处显示进一步吸收带，与长链脂质（CH₂和酯羰基）振动相符[17,18]，并在约1030、873和603/563 cm⁻¹处显示吸收带，与磷灰石样矿物相的磷酸盐和碳酸盐振动相符[19]；这些谱带在蛋白质参考光谱中缺失或较弱。在实验室报告中，蛋白质被列为所分析材料的主要成分，未列出次要成分或矿物成分；然而，这反映的是自动单组分谱库分类而非定量测量。基于这些发现，所分析材料被认为含有大量有机的、富含蛋白质和脂质的成分，其光谱特征提示可能存在少量矿物成分。由于FTIR谱带强度不能定量这些成分的相对比例，因此无法确定所分析材料中蛋白质、脂质和矿物的比例。
2.13. 术后经过与随访
患者于术后24小时出院。术后6小时恢复自主采食和饮水。48小时时进行了手术复查，当时再次更换了敷料。术后2周拆除皮肤缝线。伤口完全愈合，2周检查时无复发迹象。拆线后未再进行临床复查。术后4个月电话随访时，主人报告颈部肿胀未复发，手术伤口完全愈合，犬一般状况良好，对其生活质量满意；主人认为无需进一步临床复查。
3. 讨论
下颌–舌下腺-管复合体的实性病变在犬中不常见，大多数已报道的犬唾液腺结石起源于腮腺管；下颌腺受累主要通过个别病例报告记录[4,6,7]。如本病例中所观察到的并发唾液腺炎，已被描述与实性凝结物导致的管腔阻塞相关，后者促进继发性实质炎症[3,5]。
本病例的一项关键发现是病灶的放射学阻射程度与其生化组成之间存在显著不一致。对所提交碎片的FTIR光谱分析表明，其含有大量有机成分，富含蛋白质和脂质，并伴有提示可能存在少量矿物质成分的额外谱带，这表明切除的结构不同于传统的、以矿物质为主的涎石。这一发现与越来越多的证据相一致，即唾液腺结石的组成并非均匀的矿物质。在人类医学中，有机性和混合性涎石已被充分认识，即使在放射学上致密的结石以及其他部位的凝结物中，也已鉴定出复杂的有机基质[9,20,21,22,23]；这些观察是否适用于犬的唾液腺凝结物仍不清楚。对于一个含有如此大量有机成分的凝结物而言，其显著的放射学阻射性需要解释。与磷酸盐/碳酸盐（类磷灰石）相相符的额外光谱谱带提示，存在低于自动文库分类阈值或在该凝结物内分布不均的少量矿物质成分，这也可能解释文库匹配质量仅为中等的原因。这种少量矿物质成分，可能结合有机基质的致密压实和脱水，或可解释其放射学阻射性。组织病理学上观察到的局灶性矿化位于周围的腺体组织中，而非凝结物内，因此不能为凝结物本身的组成提供信息。此前已有报道在犬中描述过被报告为非矿物质性的阻射性涎石[7]。然而，在缺乏元素分析的情况下，这一解释仍属假设。
由于该凝结物位于腺体复合体内而非导管腔内，因此无法确立其作为导管内凝结物的分类。另一种解释是唾液囊肿，其中浓缩的唾液分泌物被肉芽组织和纤维组织构成的假包膜包裹，发生了营养不良性矿化；在犬的唾液黏液中已描述过骨化生等继发性改变[3]。抽吸液的黏液性细胞学表现、肿物柔软且波动的成分以及组织病理学上观察到的肉芽组织和纤维化，均与这一解释相符。现有发现无法区分这两种可能性。因此，“凝结物”一词仅作描述性使用，不暗示其来源于导管。
唾液腺凝结物的发病机制尚未完全阐明，此处讨论的机制主要是源自人类研究的假设，而非在本犬中证实的机制。唾液淤滞或唾液流减少被认为是核心的易感因素，可促进分泌物质在导管系统内积聚[24,25]。根据有机核心学说和逆行学说，黏液栓、糖蛋白、脱落的上皮细胞和炎性碎片，连同从口腔上行的细菌，可能形成最初的有机核心，随后有机物质以及程度不等的无机物质在其周围沉积[25,26]。继发性炎症随后可能导致纤维化和进一步的导管狭窄，可能形成淤滞、炎症和凝结物生长的自我延续循环[25]。在本犬中，总钙和磷均在参考区间内，离子钙轻度降低，这不支持高钙血症的参与；碱性磷酸酶活性升高未进一步检查，因此不能排除潜在的全身性疾病。这些假设性机制与组织病理学上发现的腺体萎缩、纤维化和涎腺炎相符，但在本病例中无法得到证实，且起始事件仍不清楚。
本病例的一个特别显著特征是凝结物体积较大，在放射学和大体检查中测量约为3.1×2.9 cm——远大于本报告中引用的犬涎石，例如Ryan等[6]描述的4 mm结石或Coutin等[4]鉴定的11×2.2 mm矿物质衰减结构。在人类医学中，超过3 cm的颌下腺结石被认为罕见，并被归类为“巨大”涎石，该阈值历史上是为矿物质性结石定义的[27]；本凝结物的最大径（3.1 cm）略超过该阈值，尽管该阈值是为人类矿物质性结石定义的，其对一个含有大量有机成分的犬凝结物的适用性尚不确定。
经腹侧或侧方颈部入路行下颌-舌下腺涎腺切除术被认为是涉及该腺体复合体的唾液囊肿和涎石病的确定性治疗方法，无论选择何种入路，完整切除腺体和导管均与低复发率相关[10,11,28]。
在本病例中，通过腹侧入路完整手术切除下颌-舌下腺复合体后，恢复顺利，术后6小时内恢复自主采食和饮水，伤口完全愈合，术后两周拆线时无复发迹象；这一良好的短期结局与该腺体复合体唾液腺切除术后的已报道结果一致[5,11]。
本报告存在若干局限性。首先，缺乏先进的横断面影像学检查，如计算机断层扫描或唾液腺造影，这些检查本可提供关于 conglomerate 精确导管或腺体定位的额外术前信息，如其他报告所述[4]。此外，仅获取了侧位X线片；由于患者焦虑和保定困难，无法获得正交的腹背位视图，这限制了对不透射线影的侧化及确切位置的放射学评估（第2.6节）。另外，临床随访仅限于术后即刻和两周拆线时；较长期随访（4个月）仅基于电话 owner 报告，未进行临床或影像学再评估，需要延长临床随访以更明确地排除晚期复发。另外四个局限性涉及成分分析。第一，FTIR光谱分析仅对提交的九个碎片进行，而非整个大体标本；因此，成分发现特异地适用于所分析的材料，不能完全排除未采样部分的成分异质性，尤其考虑到组织病理学在周围腺体组织内发现了局灶性矿化。第二，外部实验室未报告仪器层面的细节，包括采样技术、样品制备、单个碎片的处理以及参考库的身份。第三，FTIR光谱分析根据特征性酰胺吸收带对主要成分的一般生化类别进行分类，但不能分辨存在的特定蛋白质的身份；本病例中形成 conglomerate 的确切蛋白质未进一步表征，需要基于质谱的蛋白质组学等技术来确立这一点。第四，实验室报告的光谱匹配质量（54.56）低于FTIR库鉴定所用的接受标准[16]。由于库搜索将样品光谱与单组分参考光谱进行比较，混合成分（如额外的脂质和磷酸盐/碳酸盐相关吸收带所提示）可能是这种中等匹配的原因；因此，结果应解释为鉴定所分析材料的主要生化类别，而非其成分的绝对定量。最后，组织病理学检查有限。诊断基于单张Masson三色染色切片，未进行苏木精-伊红染色。 conglomerate 碎片本身未切片，因此无法评估其微观结构。矿化区域仅通过Masson三色染色识别，该方法对矿物质不特异，未经von Kossa或茜素红等矿物质特异性染色确认。未进行正交技术，如能量色散X射线光谱或X射线衍射，这些技术是确认或排除矿物成分所必需的；建议在未来此类病例中使用。
从临床角度看，本病例提示：与下颌-舌下腺复合体相关的大型、边界清晰的不透射线结构，在犬颈部肿胀的鉴别诊断中应促使考虑阻塞性唾液腺结石，即使口腔和唾液腺导管开口表现正常；仅凭放射学不透射线不能推断此类结石的成分；应考虑对取出的材料进行成分分析，最好结合光谱和元素技术，以改善对这些罕见病变的表征。
4. 结论
本病例描述了一只犬下颌-舌下唾液腺复合体相关的大型放射学不透射线 conglomerate，具有大量有机、富含蛋白质和脂质的成分，并伴有慢性唾液腺萎缩、纤维化和唾液腺炎。对提交材料的FTIR光谱分析表明存在大量富含蛋白质和脂质的有机成分，光谱特征提示可能存在少量矿物成分，表明仅凭放射学不透射线不能推断唾液腺结石的成分。手术切除受累的下颌-单口舌下腺复合体后临床完全缓解，2周检查未检测到复发， owner 在4个月时未报告复发。每当回收看似放射学不透射线的固体唾液腺相关病变时，应考虑成分分析，特别是当其大体、放射学和组织病理学特征不能明确确立矿物性结石时。
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Simple Summary
Solid lesions of the mandibular and sublingual salivary glands are rare in dogs and can be difficult to distinguish clinically from other cervical swellings. In this case report, we describe an 11-year-old Maltese dog with a large, well-defined, hard structure identified in the left cervical region on physical and radiographic examination. Surgical removal of the affected salivary gland complex retrieved a heart-shaped, solid conglomerate within the gland complex. Spectroscopic compositional analysis of the retrieved material suggested that it contained a substantial organic component rich in protein and fat (lipid), with a possible minor mineral component, whereas salivary stones are usually assumed to be mainly mineral. Microscopic examination of the surrounding tissue confirmed chronic inflammation, atrophy and scarring (fibrosis) of the gland. The dog recovered without complications and showed complete healing at two weeks after surgery. More advanced imaging, such as computed tomography, was not performed and could have helped to locate the lesion more precisely before surgery. This case illustrates that salivary lesions that appear on X-rays in dogs are not always mainly mineral, that protein-rich masses in the salivary gland should be considered in the diagnostic work-up of cervical swellings, and that surgical removal of the affected gland resulted in a favourable short-term outcome.
1. Introduction
Diseases of the salivary glands and ducts are uncommon overall in dogs and cats [1]. The mandibular gland lies between the linguofacial and maxillary veins, at the point where they unite to form the external jugular vein, and is fused to the monostomatic portion of the sublingual gland, with which it shares a closely related duct system—an anatomical relationship that explains why sialoadenectomy of this complex usually involves en bloc removal of both glands [1]. Salivary gland disorders in dogs include sialocele (salivary mucocele), sialoadenitis, sialolithiasis and neoplasia, with mucocele formation representing the most frequently reported condition and sialolithiasis considered rare in this species [2,3].
Sialoliths have been described most often in the parotid duct, whereas involvement of the mandibular–sublingual gland-duct complex is only occasionally reported, usually as isolated case reports [4,5,6,7]. Other non-obstructive parotid duct disorders, such as parotid duct ectasia, have also been described in dogs, further illustrating that salivary duct pathology in this species centres predominantly on the parotid gland rather than on the mandibular–sublingual complex [8]. Reported canine sialoliths are commonly composed of calcium carbonate or calcium phosphate, although non-mineral, protein-rich calculi have also been documented [7]. In humans, proteomic and spectroscopic studies have similarly shown that a substantial subset of sialoliths are predominantly organic or proteinaceous in composition, with mineral deposition occurring only secondarily, if at all, indicating that solid salivary-associated concretions cannot be assumed to be mineral in nature without compositional analysis [9].
Clinically, sialolithiasis of the mandibular–sublingual complex typically presents as a submandibular or cervical swelling, which may be difficult to distinguish from sialocele, abscess, foreign-body reaction or neoplasia on physical examination alone [3,5]. Plain radiography can demonstrate a mineral-opaque calculus and support the clinical suspicion, while definitive diagnosis relies on histopathological examination of the excised gland and duct [4,6]. Sialoadenectomy of the affected mandibular and sublingual glands, performed via either a ventral or lateral cervical approach, remains the standard treatment for sialocele and sialolithiasis of this gland complex, with a generally favourable long-term outcome reported in the literature [5,10,11].
We report a case of a large radiographically opaque conglomerate with a substantial organic, protein- and lipid-rich component associated with the mandibular–sublingual salivary gland complex, with secondary sialoadenitis, in a dog. The lesion was identified by clinical examination, cytology and cervical radiography, excised surgically via a ventral approach, and the surrounding glandular tissue was examined histopathologically, whereas the conglomerate itself was characterized by Fourier-transform infrared (FTIR) spectrometry. In this report, the term “conglomerate” is used for the excised lesion because its substantial organic component distinguishes it from a conventional, predominantly mineral sialolith; “sialolith” and “calculus” refer to previously reported salivary stones, and “concretion” is used as a general term encompassing both.
2. Case Presentation
2.1. Signalment
An 11-year-old, intact (non-spayed) female Maltese dog, weighing 5 kg, was presented to the surgery clinic.
2.2. History
The owners reported having first noticed the swelling accidentally, while petting the dog, approximately 3 weeks before presentation. They decided to seek veterinary care because the mass appeared to have increased markedly in size over the preceding 7 days. No changes in appetite or behaviour were noted by the owners, and the dog had not received any prior treatment for this condition.
2.3. Physical Examination
On presentation, the dog was alert, normothermic (rectal temperature 38.5 °C), with a respiratory rate of 30 breaths/min and a heart rate of 110 bpm. General physical status was unremarkable, and the dog maintained a normal appetite and water intake. A unilateral, non-painful mass, approximately 2–3 cm in diameter, was palpated in the left cervical/ventrolateral region, with mixed consistency—soft at the surface and firm in depth. Examination of the oral cavity and dentition revealed no abnormalities, and no changes were observed at the opening of the salivary duct. Regional lymph nodes (mandibular/retropharyngeal) were of normal size on palpation.
2.4. Preoperative Laboratory Findings
Preoperative complete blood count and serum biochemistry analyses were performed using a VetScan HM5 haematology analyser (Abaxis, Union City, CA, USA) and a BioSystems BA200 analyser (BioSystems, Barcelona, Spain), respectively, and are summarized in Table 1. Haematological reference intervals were those provided by the analyser manufacturer, and the biochemical reference intervals used were those of the Merck Veterinary Manual [12]. Mild increases in haemoglobin and MCH and a marked increase in alkaline phosphatase were noted, together with a mildly decreased ionized calcium concentration; the remaining parameters were within the reference intervals (Table 1).
2.5. Cardiological Assessment
Pre-anaesthetic cardiological evaluation, including auscultation, electrocardiography and transthoracic echocardiography (Vetus 8, Mindray, Shenzhen, China), revealed no abnormalities other than respiratory sinus arrhythmia and a wandering pacemaker, both considered physiological variants in dogs, and no contraindication to general anaesthesia was identified.
2.6. Diagnostic Imaging
Cervical and thoracic radiographs, including right and left lateral views, were obtained to evaluate the cervical mass using a Maxivet 400 DR digital veterinary radiography system (COMES ELECTRO S.r.l., Cavaria con Premezzo, Italy). The thoracic radiographs were obtained as part of pre-anaesthetic screening and to evaluate for possible pulmonary metastases, as neoplasia was included among the differential diagnoses. The right lateral view (Figure 1) showed the thoracic bony structures without traumatic or degenerative changes, a radiographically normal diaphragm, a trachea with sinuous course and normal calibre, and cardiovascular structures of normal radiographic appearance; the lungs showed no radiographic evidence of metastases. A well-defined, approximately ovoid radiopaque structure, measuring approximately 3.1 × 2.9 cm, was identified in the cranial cervical region, superimposed on the pharyngeal area on the lateral view, with possible lateralization; its exact localization could not be determined due to difficulty in patient restraint (the patient was anxious during the examination); for the same reason, an orthogonal ventrodorsal view, which would have helped to establish lateralization, could not be obtained. These findings raised suspicion of a salivary gland disorder associated with a solid, radiopaque structure, and a dental and surgical consultation was recommended.
2.7. Differential Diagnosis
Fine-needle aspiration of the soft, fluctuant component of the mass, performed on the day of presentation, one day before surgery, yielded clear, sero-mucous fluid. Cytological examination of the aspirated fluid revealed abundant amorphous mucinous material admixed with numerous foamy macrophages, occasional non-degenerate neutrophils, and variable numbers of erythrocytes; no cytological features of malignancy were identified in the aspirated fluid. Bacteriological examination of the aspirated fluid, submitted on the day of collection, performed at the microbiology laboratory of the Faculty of Veterinary Medicine, “Ion Ionescu de la Brad” Iași University of Life Sciences, included direct microscopic examination of a Gram-stained smear and culture on blood agar, MacConkey agar, brain heart infusion and chocolate agar, with incubation at 36 °C for 48 h; no bacterial growth was obtained; the excised tissue was not submitted for bacteriological culture. The cytological findings were consistent with salivary content, as found in a mucocele (sialocele); however, only the fluid component of the mass was sampled, and these findings were not necessarily representative of its solid component. Given the non-painful, slowly progressive cervical swelling with a mixed consistency, these cytological findings, and normal regional lymph nodes, several differential diagnoses were considered.
Sialocele (salivary mucocele) was initially considered because of the soft, fluctuant component and the mucous character of the aspirated fluid—zygomatic sialoceles and sialoceles located in the pharyngeal wall (pharyngeal sialoceles) have similarly been reported to present as slowly progressive, non-painful swellings in dogs [13,14]; however, the presence of a firm, well-defined radiopaque structure on radiographs was not typical of an uncomplicated mucocele and pointed instead towards a solid, obstructing conglomerate with secondary gland involvement. An abscess was considered less likely, although it could not be excluded on clinical grounds alone, as the mass was non-painful, the patient was afebrile and eupneic throughout the examination, and the complete blood count did not show a significant inflammatory leukogram. A foreign-body reaction was also considered given the firm component on palpation, but there was no history of trauma, oral/dental disease or foreign-body ingestion, and the well-circumscribed, ovoid radiopaque structure seen radiographically was considered more suggestive of a solid salivary-associated conglomerate than of a foreign body, although radiopacity alone did not establish its composition. Neoplasia was considered, given the patient’s age, but the absence of regional lymphadenopathy, the non-infiltrative, well-defined radiographic appearance of the mass, and the lack of pain on palpation made this differential less probable; however, as cytology had sampled only the fluid component, neoplasia could not be excluded before histopathological examination. Based on these findings, a solid obstructive conglomerate of the mandibular–sublingual gland complex with secondary sialoadenitis was considered the most likely working diagnosis, to be confirmed by surgical exploration, histopathological examination and compositional analysis.
2.8. Anaesthetic and Analgesic Protocol
Premedication consisted of methadone (Insistor, Richter Pharma AG, Wels, Austria) administered intravenously at 0.3 mg/kg (1.5 mg total dose for the 5 kg patient). General anaesthesia was induced with alfaxalone (Alfaxan, Jurox Pty Ltd., Rutherford, NSW, Australia), administered intravenously to effect (total dose 3 mg/kg), and maintained with isoflurane (IsoFlo, Zoetis Belgium SA, Louvain-la-Neuve, Belgium; 1–2%) in oxygen, with assisted (mechanical) ventilation using an R650 veterinary anaesthesia machine with an integrated ventilator (RWD Life Science Co., Ltd., Shenzhen, China); ketamine (Ketamidor, Richter Pharma AG, Wels, Austria) was administered as an intravenous bolus at 2 mg/kg during the maintenance phase for perioperative analgesia. Additional analgesia was provided by local infiltration of lidocaine (LidoBel 20 mg/mL, Bela-Pharm GmbH & Co. KG, Vechta, Germany) at multiple points along the planned incision line, at a dose of 4 mg/kg (20 mg total dose; 1 mL for the 5 kg patient). Intraoperative fluid therapy consisted of a balanced crystalloid solution (Ringer’s solution; Infomed Fluids SRL, Bucharest, Romania) administered at a constant rate of 5 mL/kg/h using an infusion pump (BeneFusion VP3 Vet, Mindray, Shenzhen, China), with fluids warmed by a blood and infusion warmer (Eickemeyer, Tuttlingen, Germany). The duration of surgery was 90 min. Intraoperative monitoring was performed with a multiparameter veterinary monitor (uMEC 10 Vet, Mindray, Shenzhen, China) and included electrocardiography, heart rate, pulse oximetry (SpO2), capnography (end-tidal CO2, EtCO2), non-invasive (oscillometric) blood pressure, respiratory rate and body temperature. Heart rate ranged from 90 to 120 bpm, SpO2 remained between 96% and 98%, EtCO2 was maintained at approximately 40 mmHg with a respiratory rate of approximately 25 breaths/min, and mean arterial pressure was maintained at approximately 70 mmHg, with no episodes of hypotension. Body temperature was 38.5 °C at induction and 38.1 °C at the end of surgery; normothermia was supported with a forced-warm-air warming system (WMS-1501, AEOLUS International Pet Products, Irving, TX, USA).
2.9. Surgical Technique
A ventral paramedian approach was selected to expose and excise the affected mandibular–monostomatic sublingual salivary gland complex. This approach provides direct access to the mandibular and monostomatic sublingual salivary glands and has been associated with a lower risk of recurrence than the lateral approach in dogs undergoing sialoadenectomy for sialocele, although wound-related complications may be more frequent [15]. The patient was positioned in dorsal recumbency (Figure 2A). A 3–4 cm paramedian skin incision was made along the longitudinal axis of the swelling, approximately 10 mm from the external jugular vein. The linguofacial vein was identified near its union with the maxillary vein to form the external jugular vein (Figure 2B). The linguofacial vein was closely apposed to and partially adherent to the capsule of the mandibular salivary gland; it was carefully dissected free while preserving its integrity. The mandibular salivary gland and monostomatic sublingual salivary gland were exposed as a single glandular complex. The glandular branch of the facial artery was identified and ligated (Figure 3A). Dissection was continued until the mandibular and sublingual ducts were identified; the ducts were dissected for a short distance from the glandular complex and then ligated with 3-0 absorbable monofilament suture material and transected close to the gland (Figure 3B). The glandular complex was then removed en bloc through the skin incision, aided by gentle stretching of the skin edges. Its gross appearance, still enclosed within its capsule, is shown in Figure 4A. Following removal of the capsule, a heart-shaped, solid conglomerate was retrieved from within the glandular complex (Figure 4B); the conglomerate was located within the glandular complex and was not found within the lumen of the mandibular or sublingual duct; its appearance after sectioning is shown in Figure 4C. After sectioning, the conglomerate was divided into a fragment of approximately 2 × 1.5 cm, which was submitted for histopathological examination together with the glandular tissue (Section 2.11), and the remaining material, which was submitted for FTIR spectrometric analysis (Section 2.12). The surgical site was closed in two layers using 3-0 absorbable monofilament suture material: the subcutaneous tissue with a continuous pattern and the skin with simple interrupted sutures.
2.10. Perioperative and Postoperative Medication
Postoperative anti-inflammatory and analgesic treatment consisted of meloxicam (Melovem injectable, Dopharma Research B.V., Raamsdonksveer, The Netherlands), administered subcutaneously at 0.2 mg/kg immediately after surgery, followed by an oral suspension of meloxicam (Rheumocam, Chanelle Pharmaceuticals Manufacturing Ltd., Loughrea, Ireland) at 0.1 mg/kg once daily for a further 4 days. Antibiotic therapy consisted of amoxicillin-clavulanate (Kesium, Ceva Santé Animale, Libourne, France), administered orally at 12.5 mg/kg every 12 h for 5 days. This treatment was initiated empirically, before the bacteriological result was available (the 48-h culture of the aspirate collected one day before surgery was still pending), because of the suspected secondary sialoadenitis and the surgical exposure of a ductal system communicating with the oral cavity, and was completed as a short course. The surgical dressing was changed at 24 h postoperatively.
2.11. Gross and Histopathological Examination
Histopathological examination was performed on the excised glandular complex, fixed in 10% formalin; one section stained with Masson’s trichrome was examined, and routine haematoxylin and eosin (H&E) staining was not performed (Figure 5). A fragment of the conglomerate (approximately 2 × 1.5 cm), white in colour, with a rough surface and hard consistency, was submitted together with the glandular tissue but was not sectioned; only the glandular tissue was processed and examined histologically, and no mineral-specific stain (e.g., von Kossa or Alizarin red) was performed. The surrounding tissue, consistent with residual salivary gland parenchyma and/or excretory duct, contained occasional groups of secretory-type epithelial cells with foamy cytoplasm and centrally located nuclei, together with cells showing basophilic, granular cytoplasm, possibly originating from a mixed salivary acinus. Fibrous connective tissue predominated, with numerous newly formed vessels giving a granulation-tissue-like appearance in some areas (Figure 5A). A mixed inflammatory infiltrate and areas of haemorrhage (Figure 5B), as well as areas consistent with mineralization (Figure 5C), were also observed. Adipose tissue infiltration was also present within the fibrous stroma (Figure 5A). The excised specimen included a lymph node with a largely preserved follicular architecture, mildly rarefied predominantly in the cortical zone, showing haemosiderosis and lipofuscinosis. The histopathological diagnosis was salivary gland atrophy, fibrosis, and sialoadenitis.
2.12. Fourier-Transform Infrared (FTIR) Spectrometric Analysis of the Conglomerate
The remaining material of the excised conglomerate (Section 2.9) was submitted to an external accredited diagnostic laboratory (Laboklin GmbH & Co. KG, Bad Kissingen, Germany) for compositional analysis by Fourier-transform infrared (FTIR) spectrometry. The analysis was performed within the laboratory’s accredited scope for stone analysis, which includes salivary calculi of all animal species. The submitted material, as described in the laboratory report, comprised nine beige fragments with a rough surface, ranging in size from approximately 1 × 1 mm to 22 × 22 mm. The material was white when retrieved at surgery and had become beige by the time of analysis, probably as a result of dehydration, which may also have reduced the size of the fragments. The FTIR spectrum of the sample (Figure 6) was compared against the laboratory’s reference spectral library using automated library-search software Opus version 8.5; the closest match was to a protein reference spectrum, with a reported match quality of 54.56. This value represents the similarity index generated by the laboratory’s library-search software, with higher values indicating closer agreement between the sample and reference spectra; a value of 54.56 falls below the acceptance criteria used for FTIR library identification of uroliths. Acceptance criteria are software- and laboratory-specific; in a published protocol for canine urolith analysis, hit-quality values of at least 800 on a 0–1000 scale are considered high-confidence and values of 700–800 tentative [16]. The laboratory did not report the scale or acceptance criterion applied, but a value of 54.56 falls below these criteria whether expressed on a 0–100 or a 0–1000 scale. Both the sample spectrum and the reference spectrum showed the broad amide A/B absorption band near 3300–3000 cm−1 and the characteristic amide I and amide II bands near 1650 cm−1 and 1550 cm−1, consistent with peptide backbone vibrations of a proteinaceous matrix [17]. In addition to the amide bands, the sample spectrum showed further absorption bands at approximately 2920/2850, 1740, 1465 and 720 cm−1, compatible with long-chain lipid (CH2 and ester carbonyl) vibrations [17,18], and at approximately 1030, 873 and 603/563 cm−1, compatible with phosphate and carbonate vibrations of an apatite-like mineral phase [19]; these bands were absent from, or weak in, the protein reference spectrum. In the laboratory report, proteins were listed as the main constituent of the analysed material, and no minor or mineral constituent was listed; however, this reflects the automated single-component library classification rather than a quantitative measurement. On the basis of these findings, the analysed material was considered to contain a substantial organic, protein- and lipid-rich component, with spectral features suggesting a possible minor mineral component. Because FTIR band intensities do not quantify the relative proportions of these constituents, the proportions of protein, lipid and mineral in the analysed material could not be determined.
2.13. Postoperative Course and Follow-Up
The patient was discharged 24 h after surgery. Voluntary food and water intake resumed 6 h postoperatively. A surgical recheck was performed at 48 h, at which time the dressing was changed again. Skin sutures were removed at 2 weeks postoperatively. Complete wound healing was achieved, with no evidence of recurrence at the 2-week examination. No further clinical re-examination was performed after suture removal. At telephone follow-up 4 months postoperatively, the owner reported no recurrence of the cervical swelling, complete healing of the surgical wound and a good general condition of the dog, and was satisfied with its quality of life; the owner considered a further clinical re-examination unnecessary.
3. Discussion
Solid lesions of the mandibular–sublingual gland-duct complex are uncommon in dogs, and most reported canine sialoliths originate in the parotid duct; involvement of the mandibular gland has been documented mainly through isolated case reports [4,6,7]. Concurrent sialoadenitis, as observed in the present case, has been described in association with ductal obstruction by a solid concretion, which promotes secondary parenchymal inflammation [3,5].
A key finding of the present case was the marked discordance between the radiographic opacity of the lesion and its biochemical composition. FTIR spectrometry of the submitted fragments indicated a substantial organic, protein- and lipid-rich component, with additional bands suggesting a possible minor mineral component, indicating that the excised structure differed from a conventional, predominantly mineral sialolith. This finding is consistent with a growing body of evidence that salivary calculi are not uniformly mineral in composition. In human medicine, organic and mixed sialoliths are well recognized, and complex organic matrices have been identified even in radiographically dense calculi and in concretions at other sites [9,20,21,22,23]; whether these observations apply to canine salivary concretions remains unknown. The marked radiographic opacity of a conglomerate with such a substantial organic component requires explanation. The additional spectral bands compatible with a phosphate/carbonate (apatite-like) phase suggest that a minor mineral fraction, below the threshold for automated library classification or unevenly distributed within the conglomerate, was present and may also account for the only moderate library match quality. Such a minor mineral fraction, possibly combined with dense compaction and dehydration of the organic matrix, may explain the radiographic opacity. The focal mineralization observed histopathologically was located in the surrounding glandular tissue, not in the conglomerate, and therefore does not inform the composition of the conglomerate itself. Radiopaque sialoliths reported as non-mineral have previously been described in dogs [7]. In the absence of elemental analysis, however, this interpretation remains hypothetical.
Because the conglomerate was located within the glandular complex rather than within the duct lumen, its classification as a ductal concretion could not be established. An alternative interpretation is a sialocele in which inspissated salivary secretion, enclosed by a pseudocapsule of granulation tissue and fibrous tissue, underwent dystrophic mineralization; secondary changes such as osseous metaplasia have been described within salivary mucoceles in dogs [3]. The mucinous cytology of the aspirated fluid, the soft, fluctuant component of the mass and the granulation tissue and fibrosis observed histopathologically would be compatible with this interpretation. The available findings did not allow these two possibilities to be distinguished. The term “conglomerate” is therefore used descriptively, without implying a ductal origin.
The pathogenesis of salivary concretions has not been fully elucidated, and the mechanisms discussed here are hypotheses derived largely from human studies rather than mechanisms demonstrated in the present dog. Salivary stasis or reduced salivary flow is considered a central predisposing factor, promoting the accumulation of secretory material within the duct system [24,25]. According to the organic-nidus and retrograde theories, mucous plugs, glycoproteins, desquamated epithelial cells and inflammatory debris, together with bacteria ascending from the oral cavity, may form an initial organic core, around which further organic and, variably, inorganic material is deposited [25,26]. Secondary inflammation may subsequently lead to fibrosis and further ductal narrowing, potentially establishing a self-perpetuating cycle of stasis, inflammation and concretion growth [25]. In the present dog, total calcium and phosphorus were within the reference intervals, and ionized calcium was mildly decreased, which does not support a hypercalcaemic contribution; the increased alkaline phosphatase activity was not further investigated, and an underlying systemic condition therefore cannot be excluded. These hypothetical mechanisms would be compatible with the glandular atrophy, fibrosis and sialoadenitis identified histopathologically, but they could not be demonstrated in the present case, and the initiating event remains unknown.
A particularly notable feature of the present case is the large size of the conglomerate, measuring approximately 3.1 × 2.9 cm on radiographic and gross examination—considerably larger than the canine sialoliths cited in this report, such as the 4 mm calculus described by Ryan et al. [6] or the 11 × 2.2 mm mineral-attenuating structure identified by Coutin et al. [4]. In human medicine, submandibular calculi exceeding 3 cm are considered rare and are classified as “giant” sialoliths, a threshold historically defined for mineral calculi [27]; the maximum dimension of the present conglomerate (3.1 cm) slightly exceeds this threshold, although the threshold was defined for human mineral calculi and its applicability to a concretion with a substantial organic component in a dog is uncertain.
Mandibular–sublingual sialoadenectomy via a ventral or lateral cervical approach is considered the definitive treatment for sialocele and sialolithiasis involving this gland complex, and complete excision of the gland and duct is associated with a low recurrence rate regardless of the approach chosen [10,11,28].
In the present case, complete surgical excision of the mandibular and sublingual glandular complex via a ventral approach resulted in an uneventful recovery, with resumption of voluntary food and water intake within 6 h after surgery and complete wound healing without evidence of recurrence at the time of suture removal, two weeks postoperatively; this favourable short-term outcome is consistent with the results reported after sialoadenectomy of this gland complex [5,11].
This report has several limitations. First, there was the absence of advanced cross-sectional imaging, such as computed tomography or sialography, which could have provided additional preoperative information on the precise ductal or glandular localization of the conglomerate, as described in other reports [4]. Furthermore, only lateral radiographic views were obtained; an orthogonal ventrodorsal view could not be acquired because of the patient’s anxiety and difficult restraint, which limited the radiographic assessment of the lateralization and exact location of the opacity (Section 2.6). In addition, clinical follow-up was limited to the immediate postoperative period and to suture removal at two weeks; longer-term follow-up (4 months) was based solely on owner report by telephone, without clinical or imaging reassessment, and extended clinical follow-up would be required to more definitively exclude late recurrence. Four further limitations relate to the compositional analysis. First, FTIR spectrometry was performed on nine submitted fragments rather than on the entire gross specimen; therefore, the compositional findings apply specifically to the analysed material and cannot fully exclude compositional heterogeneity in unsampled portions, particularly given that histopathology identified focal mineralization within the surrounding glandular tissue. Second, instrument-level details, including the sampling technique, sample preparation, handling of the individual fragments and the identity of the reference library, were not reported by the external laboratory. Third, FTIR spectrometry classifies the general biochemical class of the dominant constituent based on characteristic amide absorption bands but does not resolve the identity of the specific protein(s) present; the exact protein(s) forming the conglomerate were not further characterized in this case, and techniques such as mass-spectrometry-based proteomics would be required to establish this. Fourth, the spectral match quality reported by the laboratory (54.56) was below the acceptance criteria used for FTIR library identification [16]. Because library searching compares the sample spectrum with single-component reference spectra, a mixed composition, as suggested by the additional lipid- and phosphate/carbonate-related absorption bands, is a likely contributor to this moderate match; the result should therefore be interpreted as identifying the dominant biochemical class of the analysed material rather than as an absolute quantification of its composition. Finally, the histopathological examination was limited. The diagnosis was based on a single section stained with Masson’s trichrome, without haematoxylin and eosin staining. The conglomerate fragment itself was not sectioned, so its microscopic structure could not be assessed. The areas of mineralization were identified on Masson’s trichrome alone, which is not specific for mineral, without confirmation by a mineral-specific stain such as von Kossa or Alizarin red. Orthogonal techniques, such as energy-dispersive X-ray spectroscopy or X-ray diffraction, were not performed and would be required to confirm or exclude a mineral component; their use is recommended in future cases of this type.
From a clinical perspective, this case suggests that a large, well-defined radiopaque structure associated with the mandibular–sublingual gland complex should prompt consideration of an obstructive salivary concretion in the differential diagnosis of cervical swellings in dogs, even when the oral cavity and salivary duct opening appear normal; that radiographic opacity alone does not allow the composition of such a concretion to be inferred; and that compositional analysis of the retrieved material, ideally combining spectroscopic and elemental techniques, should be considered to improve the characterization of these uncommon lesions.
4. Conclusions
This case describes a large radiographically opaque conglomerate with a substantial organic, protein- and lipid-rich component associated with the mandibular–sublingual salivary gland complex in a dog and accompanied by chronic salivary gland atrophy, fibrosis and sialoadenitis. FTIR spectrometry of the submitted material indicated a substantial protein- and lipid-rich organic component, with spectral features suggesting a possible minor mineral component, indicating that radiopacity alone does not allow the composition of a salivary concretion to be inferred. Surgical excision of the affected mandibular–monostomatic sublingual gland complex resulted in complete clinical resolution, with no recurrence detected at the 2-week examination and none reported by the owner at 4 months. Compositional analysis should be considered whenever solid salivary-associated lesions that appear radiopaque on radiographs are recovered, particularly when their gross, radiographic and histopathological features do not unequivocally establish a mineral calculus.