We have read with interest the article titled “Eagle Syndrome as a Cause of Cerebral Venous Sinus Thrombosis” by Fu-Liang Zhang et al. published in the May 2019 issue of The Canadian Journal of Neurological Sciences.^{Reference Zhang, Zhou, Guo and Yang1}

The authors describe a case of Eagle syndrome in a 15-year-old teenager with a 2-month history of headache that was caused by left transverse-sigmoid sinus thrombosis due to compression of the left jugular vein by an elongated styloid process (SP). This is quite unusual, since the classic Eagle syndrome is primarily caused by compression of the internal carotid artery, resulting in a wide spectrum of clinical and neuroradiological findings from cervicofacial pain to cerebral ischemia.^{Reference Chung, Chao, Hsu, Lin and Hu2,Reference Galletta, Granata and Longo3}

The paper by Fu-Liang Zhang deserves merit since it describes an unusual effect of the presence of elongated SPs, i.e., compression of the jugular vein, leading to some interesting considerations regarding what has been defined as “Eagle jugular syndrome.”^{Reference Galletta, Siniscalchi, Ciccio, Velo and Granata4} It is well known that prolonged venous compression can lead to the development of deep venous thrombosis (DVT). DVT is much more frequent in the lower limbs, but it may occur in any section of the venous system, including arms, abdominal, and also the jugular veins.^{Reference Illig and Doyle5} For instance, thrombosis of the subclavian vein at the costoclavicular junctions, also known as Paget-Schroetter syndrome, is caused by intermittent venous compression due to muscular stretch in the thoracic outlet and may potentially result in pulmonary embolism initially classified as of unknown origin.^{Reference Martinelli6}

Similarly, it has already been demonstrated that compression of the jugular vein caused by an elongated SP may result in jugular thrombosis, thus configuring the case of “Eagle jugular syndrome.” In such a scenario, clinical manifestations may vary from migraine to cerebral venous thrombosis.^{Reference Galletta, Siniscalchi, Ciccio, Velo and Granata4,Reference Porfidia, Porceddu and Feliciani7}

In light of such evidence, it is reasonable to hypothesize that jugular vein thrombosis may also lead to pulmonary embolism. It has been reported that in approximately 20% of cases of pulmonary embolism, the source of emboli cannot be identified, representing the so-called “isolated pulmonary embolism,” which is frequently caused by unusual forms of venous thrombosis and thrombophilia.^{Reference Siniscalchi8} It could be speculated that jugular vein thrombosis in Eagle syndrome may be responsible for some of these cases of pulmonary embolism, given that this eventuality has been poorly investigated.

Our suggestion is to include also the investigation of jugular vein compression due to elongated SPs in cases of pulmonary embolism of unknown origin. As previously reported, we strongly support the necessity of a dynamic evaluation of compression of neck structures due to elongated SPs in Eagle syndrome.^{Reference Zamboni, Scerrati and Menegatti9} The diagnostic accuracy of computed tomography angiography (CTA)/magnetic resonance angiography (MRA) can be increased through a “dynamic” evaluation of the spatial relationship between SPs and neck vascular structures simply performing acquisitions using different orientations of the head. This could better identify the compression that occurs only with a specific head orientation (e.g. rotation) but not in a “neutral” head position.

In conclusion, we think that, amongst others, Eagle syndrome may result in compression and thrombosis of the jugular vein, thus causing life-threatening clinical manifestations, including cerebral venous thrombosis, as reported by Fu-Liang Zhang et al.,^{Reference Zhang, Zhou, Guo and Yang1} along with isolated, recurrent, pulmonary embolism events, the origin of which may be misdiagnosed. The dynamic exploration of the spatial relationship between elongated SPs and jugular veins though CTA and/or MRA may lead to a prompt diagnosis of this eventuality and to an effective treatment of these patients. Further investigations are needed to confirm or deny our hypothesis.