Simultaneous Baker's cyst rupture and deep venous thrombosis accompanied by acute pulmonary embolism

A 79-year-old woman presented with a 2-week history of swelling in the left knee and pain during exercise without any triggers. She was referred to our emergency department with a 1-week history of an inability to eat and gradually worsening knee pain and swelling that prevented walking. The patient had obesity, diabetes, and a history of venous thromboembolism. Hypoxia and tachycardia were present, with an oxygen saturation of 93%, a pulse of 106 beats per minute, and an elevated d-dimer level (18.02 μg/mL). Lower-leg vein ultrasonography revealed fluid accumulation with different internal components along the medial fascia of the left knee fossa continuous within the knee joint space (Figure 1A-1, A-2). A deep venous thrombosis (DVT) was observed in the left proximal popliteal vein to the peroneal vein extending from the popliteal fossa to the middle of the lower leg (Figure 1B-1–B-3). Contrast-enhanced lower-extremity computed tomography (CT) revealed mixed concentrations of liquid components and DVT (Figure 2A). The liquid components were continuous in the knee joint space. Contrast-enhanced chest CT revealed thrombotic occlusion of both pulmonary arteries (Figure 2B) and reduced pulmonary blood flow (Figure 2C-1,C-2). The patient was diagnosed with a ruptured Baker's cyst and DVT complicated by acute pulmonary embolism (PE). The patient was treated with anticoagulation therapy with attention to hemodynamics and bleeding, and no worsening of the lower-extremity symptoms was observed. A contrast-enhanced CT performed 3 months later showed that the thrombi in the pulmonary arteries and deep veins had disappeared and that the thrombi in the Baker's cyst were homogeneous at low concentrations (Figure 3). A Baker's cyst rupture is called pseudothrombophlebitis because its symptoms resemble those of thrombophlebitis.1 Although a Baker's cyst rupture rarely causes DVT, it is difficult to distinguish from DVT because of their similar clinical manifestations. To diagnose a Baker's cyst on ultrasonography, in addition to the presence of a cyst located between the medial head of the gastrocnemius muscle and the semitendinosus muscle at the knee socket, fluid retention with a hypoechoic area around the medial leg muscle that would be traversed by it upon rupture must also be present. Furthermore, the liquid components are continuous with the knee joint space. Ultrasonography has high diagnostic accuracy for Baker's cysts and is a rapid and useful early diagnostic method.2, 3 A recent report concluded that Baker's cysts were not associated with DVT development.4 Although rare, there have been reports of PE secondary to DVT caused by compression of the popliteal vein by a Baker's cyst.5 However, we found no reports of acute PE after Baker's cyst rupture and DVT. It is possible that Baker's cyst rupture was a contributing factor to the DVT and PE in this case, but it is also possible that these findings were incidentally comorbid. In addition to dehydration, the patient had a history of obesity, diabetes mellitus, and venous thromboembolism, which may have been related to the development of DVT and PE. On the other hand, although rare, we cannot rule out the possibility of venous compression due to lower-extremity swelling associated with the Baker's cyst rupture, pain-related movement limitations, and blood-flow stagnation due to insufficient fluid intake. DVT and Baker's cyst rupture may coexist when pain, swelling, and redness around the knee are present; however, this is rare. Ultrasonography is likely to detect the comorbidity of this disease at an early stage and prevent misdiagnosis. This case demonstrated that, although rare, a Baker's cyst rupture may be associated with DVT and an increased risk of PE. All authors have contributed to the preparation of this manuscript and agree to the content of the manuscript. We thank the sonographers at the Vascular Ultrasound Laboratory of Fukui-ken Saiseikai Hospital. We would like to thank Editage (www.editage.jp) for the English language editing. The authors declare no conflicts of interest.