The etiopathogenetic mechanism of the elongation of the styloid process has not been ascertained so far; development abnormalities and/or bone homeostasis alterations have been proposed in order to explain the occurrence of ossification or elongation of the stylohyoid process . Symptoms of the classic Eagle syndrome have been associated mainly to an intermittent compressive neuropathy involving different branches of cranial nerves, which is often exacerbated by swallowing and yawning [1-7]. These symptoms are caused by a mass effect on cranial nerves eliciting a neuropathic pain which poorly responds to medications. Nowadays the literature tends to support that surgical treatment results in a more definitive treatment and long lasting symptomatic relief . Other symptoms reported in literature are sense of hypopharyngeal foreign body, odynophagia, dysphagia in addition to cervico-facial pain with different irradiations. Cases of Horner's syndrome are usually explained with the compression of the nerve fibers of sympathetic nervous system . Apart from the classic pattern, also a ‘carotid’ variant has been described, where peculiar symptoms such as arterial dissection, obstruction, transient ischemic attack and cerebral ischemia were found associated [8-11]. It is more difficult to explain cases of Eagle syndrome associated with migraine and headache, which could be more consistently related to the external compression of internal jugular vein (Fig. 1).
Both at surgery and CTA the classic group did not show any involvement of the jugular vein, and this may explain us the lack of headache in our classic group (Table 1).
Clinically relevant extrinsic compression on the extracranial internal jugular vein (IJV) due to an elongated styloid process has been rarely described in literature. A study by Jayaraman et al. 12 enrolled 108 patients whose CT angios were investigated for the incidence of internal jugular vein compression by extrinsic structures in the upper neck. They found 24.1% right side compressions and 30.6% left side compressions. They concluded that jugular vein compression is an anatomic variant and unlikely to be pathologic in nature. However, they did not investigate about the reasons why these CT angios were performed or patients clinical history .
We collected 8 cases of Eagle jugular syndrome. In our study the symptomatology is readily different respect the to the classic or the carotid syndrome, where ipsilateral pain was the more significant symptom (Table 1). Headache, numbness and dizziness are usually chronic in the jugular group and may be related to the impaired cerebral venous outflow. Subarachnoid hemorrhage usually presents with an acute headache (described as the worst headache ever) often associated to vomiting and altered consciousness. In few studies the compression of the IJV was related to pseudotumor cerebri [13, 14] or to headaches . In many others, the jugular variant was significantly associated with persistent headache, and among comorbidities, to the peri-mesencephalic subarachnoid hemorrhage (p-SAH), both possibly related to cerebral venous hypertension [15, 16, 22, 23]. p-SAH is a particular kind of subarachnoid hemorrhage not associated to an evident vascular malformation, like aneurysms or arteriovenous malformations and with an usually good prognosis. The blood is mainly located in the cerebral basal cisterns and the cause is still debated. Among the hypothesized causes, a hypertensive venous bleeding (like coming from a particular variant of Basal vein of Rosenthal or an occluded venous sinus) is the most reliable [22, 23].
The relationship between the upper internal jugular vein bone nutcracker and the p-SAH could be a novel and intriguing finding. This variety of the subarachnoid hemorrhage is thought to be caused mainly by intracranial venous anomalies, but there are no reports in literature about its relationship with extracranial venous anomalies [22, 23]. In our series imaging at the intracranial level completely excluded the presence of any kind of vascular anomalies. However we hypothesized a jugular compression with a transient related venous hypertension could be a predisposing factor able to facilitate a p-SAH. On the basis of our study, if p-SAH should occur, we suggest to extend also at the extracranial level the investigation of the brain vasculature, focusing particularly to the extracranial veins (Fig. 1). We also know that the compression of the upper segments of the internal jugular vein can induce chronic intracranial hypertension , which was not found in our survey, yet.
CDU investigation allowed us to assess the venous haemodynamics in terms of flow velocity and flow rate of the internal jugular vein, especially just below the nutcracker, in the upper part of the neck. (Fig. 2) In the more severe cases the internal jugular vein appeared an empty vein, with no Doppler detectable flow in the lumen, even in favor of gravity with the head of the patients in upright position. Out of the initial assessment, CDU permits also to perform a precise and non-invasive follow-up of patients conservatively treated, in order to monitor any further flow worsening.
In our experience, the treatment is usually conservative, especially when symptoms are not invalidating and apparently controlled by medical treatment. Only one patient underwent surgery and endovascular balloon angioplasty, with intriguing results (see illustrative case). In this case both headache and facial edema did not respond to conservative treatment. Indeed, Higgins et al.  stated that in their group of patients with idiopathic intracranial hypertension and impairment in venous outflow, most of those who benefited only did so after subsequent jugular stenting reinforced the surgical decompression. Moreover, Zhou et al.  reported in the same field their positive experience with exclusive jugular stenting in a group of 15 patients with IJV stenosis, but without bone compression.
Someone may argue that a potential indication could the prevention of recurrent episodes of cerebral hemorrhage. However, this is a rare eventuality following p-SAH (1/1220 as reported by Mensing et al. ).
The major limitation of our study is to be a retrospective analysis. Indeed for the jugular variant we retrospectively enrolled 8 patients which are not enough to imply causation.