Thrombophlebitis of the internal jugular vein is a rare but life-threatening complication of DNSI, also known as LS. The formation of blood clots is related to hemodynamic changes, increased blood viscosity, and endothelial damage [6]. The cause of thrombus formation in this patient may be related to direct compression of the internal jugular vein by the abscess, leading to hemodynamic changes. In addition, it may also be related to endothelial damage. Following endothelial damage, subendothelial collagen becomes exposed, facilitating platelet adhesion to the collagen surface. This process triggers platelet signaling pathways, resulting in platelet activation and the release of endogenous ADP and TXA2. Consequently, additional platelets are recruited to adhere to one another, leading to irreversible platelet aggregation. Concurrently, the coagulation system is activated, inducing localized blood coagulation. Soluble fibrinogen in the plasma is converted into insoluble fibrinogen, ultimately forming a blood clot to halt bleeding. The patient had a history of a fishbone injury in the pharynx, suggesting a pharyngeal source of infection. The possible pathogenesis is that bacteria or viruses damage the mucosal barrier of the oropharynx, enter the cervical space, and then spread to the internal jugular vein through direct extension, lymphatic and hematogenous dissemination, leading to phlebitis. The endothelium of the vein is damaged, the pathogen activates platelets, activates the coagulation cascade, and thus forms a thrombus [7]. The lungs are the most common site of metastasis, accounting for 85% of all secondary infections. Common pulmonary lesions are necrotic cavities, but they can also present as pneumonia, pleural effusion, empyema, lung abscess, and necrotizing mediastinitis [8, 9]. This patient presented with pulmonary embolism, pneumonia, and a small amount of pleural effusion in the lungs. Due to timely antimicrobial and anticoagulant therapy, the patient’s condition did not worsen, avoiding possible fatal diseases. Due to the destructive effect of hemolysin produced by the pathogenic bacteria, the consumption of thrombus formation, and bone marrow suppression, the patient’s platelet count often decreases and clotting disorders may occur [10]. The most common pathogen of LS is Fusobacterium necrophorum. Although the positive rate of blood culture for F. necrophorum is low, the detection of F. necrophorum and other pathogenic bacteria in blood culture is still an important diagnostic criterion for LS. Therefore, blood culture should be performed early for febrile patients to identify pathogens. The blood culture of this patient was positive for streptococcus anginosus. To our knowledge, there are few reports of cases of streptococcus anginosus infection, and there are also few reports of deep cervical abscesses occurring in cases like our patient. The early symptoms of LS lack specificity. If there is persistent high fever or neck tenderness, LS should be highly suspected [11]. B-ultrasound is convenient, radiation-free, and can quickly detect the location and size of cervical venous thrombosis, which is of great significance for diagnosis [12], but its sensitivity for deep cervical tissue and newly formed thrombus is low [13]. Contrast-enhanced CT is the best method for diagnosing LS because it can not only show internal jugular vein thrombosis but also reveal complications such as pulmonary embolism, empyema, osteomyelitis, and brain abscesses, and epidural abscesses [14]. It is often used as a gold standard to evaluate the scope of soft tissue infections in the neck [2]. In addition, contrast-enhanced MRI has good soft tissue contrast and multi-planar relationships, which can well distinguish the relationship between blood vessels, abscesses, and adjacent soft tissues.

The treatment of LS mainly includes antimicrobial therapy, surgical intervention, and anticoagulation therapy. Antibiotics that are resistant to β-lactamase hydrolysis and have anaerobic activity should be selected [11, 14], and the treatment course is 3–6 weeks [8]. Surgical intervention can be used for severe cases, which can prevent the production of further septic emboli and should be performed by the corresponding surgeon who is in contact with the abscess site, including periodontal disease treatment and abscess incision and drainage. If the abscess is not controlled, it may develop into a severe cervical and facial soft tissue infection [15]. Regarding abscess treatment, in this patient, immediate empiric treatment with intravenous broad-spectrum antibiotics covering anaerobic bacteria were prioritized until the pathogenic bacteria were identified. As inflammatory markers significantly decreased after antimicrobial therapy, the antibiotics were not changed. In addition, surgical drainage was performed on the infection site. Due to the low incidence of LS, it is difficult to obtain randomized controlled studies to verify the risks and benefits of anticoagulation therapy. Anticoagulation therapy is still controversial, but it is recommended to use anticoagulation therapy for expanding thrombus scope, persistent high fever, or the appearance of retrograde cerebral venous sinus thrombosis. The treatment course is 6–12 weeks [16]. The American College of Chest Physicians’ 2012 guidelines recommend anticoagulation therapy for 3 months in patients with non-progressive cervical internal venous thrombosis, which can reduce the risk of recurrent thrombotic embolism [17]. For patients who cannot control the condition even with adequate antibiotic and anticoagulation therapy, ligation or surgical removal of the internal jugular vein can be selected. In this case, the patient’s thrombus did not expand after antimicrobial and rivaroxaban anticoagulation therapy. The internal jugular vein thrombosis measures approximately 4.5 cm in length, extending from the upper segment below the bifurcation of the common carotid artery to the lower segment below the subclavian vein. Due to the significant surgical complexity and the associated high risk, ligation of the thrombosed vein was not chosen as the preferred approach.