Ophthalmic Manifestations of Sinus Pericranii
Sinus pericranii (SP) is a very rare venous malformation characterized by an aberrant connection between the intracranial and extracranial venous systems. It was first described by Hecker in 1845 and was given its modern name by Stromeyer in 1850.
Mastin proposed that SP can arise through congenital, traumatic, or spontaneous means (1). SP has been associated with craniosynostosis, dural sinus hypoplasia, Crouzon syndrome, Apert syndrome and Hunter syndrome. Additionally, up to 20% of SP patients are reported to have vascular malformations elsewhere as well.
The congenital hypothesis describes SP as forming in a similar manner as other congenital true angiomas such as venous angiomas and cavernous hemangiomas. It has also been theorized that increased intracranial venous pressure during the late embryonic period can result in the formation of SP. Spontaneous origin is thought to be from the development of a varix with subsequent erosion of the skull due to pathological means.
Because SP is commonly found at the sites of previous head injuries, an acquired post-traumatic etiology has also been proposed. This trauma can lead to a torn emissary vein or injuries to intracranial sinuses, eventually triggering the formation of abnormal connections between the extracranial and intracranial venous systems. Through similar means, minor forces such as coughing and vomiting can lead to the development of communicating blood cysts at the surface of the skull.
Histological analysis of the congenital type of SP reveals the presence of thickened stroma. The traumatic type of SP is usually composed of a fibrous microstructure encapsulating the blood, which can be explained by the trauma disrupting the emissary veins and calvarium, leading to the formation of a fibrous lining or capsule around the extravasated blood.
Though the etiology of SP remains unclear, it tends to arise in the pediatric population. This is generally through either congenital or traumatic means. The distribution is equal among both sexes when congenital, however traumatic SP occurs more often in males.
Ophthalmic findings in SP are rare due to the location of the aberrant vascular connection usually occurring at the frontal and parietal regions (>80%). To our knowledge, there have only been 6 reported cases of the ophthalmic findings of SP in the English language, ophthalmic literature. These findings include compressible pulsatile and non-pulsatile masses in the orbital region that generally vary in size based on position (e.g. increase with Valsalva and decrease with standing). This increased orbital pressure can also lead to ptosis and proptosis with potential obstruction of the visual field.
The diagnosis of SP can be suspected after a comprehensive patient history and physical exam. The presence of risk factors such as young age, recent trauma, and congenital anomalies such as craniosynostosis or other neurologic findings can help suggest SP. Though usually asymptomatic, patients can present with mild symptoms such as headache, nausea, and vertigo. A suggestive feature on physical examination includes the appearance of a soft, fluctuant mass located near the intracranial sinus, which varies in size with changes in the intracranial pressure.
Neuroimaging of the suspected SP includes ultrasonography and color-Doppler scans. Computed tomography (CT) of the brain and orbit (including bone windows) may demonstrate the characteristic bony defect of SP. Magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) can demonstrate the presence of the SP and its drainage into the dural venous sinuses. MR evaluation should also include assessment of the superficial cortical veins adjacent to the SP, associated venous anomalies, and the maturation of the jugular bulbs as well as the other venous outlets of the brain. Digital subtraction angiography (DSA) can be performed to assess the intracranial venous dynamics and the role of the SP in venous drainage.
The differential diagnosis of SP includes subepicranial varix, cavernous hemangioma, arteriovenous malformation, subepicranial hygroma, eosinophilic granuloma, epidermoid tumor, dermoid tumor, meningocele, encephalocele, meningoencephalocele, traumatic leptomeningeal cyst, and cephalohematoma. In most circumstances, the diagnosis can be made from a combination of clinical and radiological features.
In contrast to SP, cavernous hemangiomas of the scalp are located in the subcutaneous space. They do not adhere to the skull bone or communicate directly with the intracranial venous sinus. In the case of the SP, the venous blood travels from the intracranial venous sinus and drains back into the same sinuses or into other extracranial venous channels. Cavernous hemangiomas do not reduce completely with external pressure.
Since SP is generally asymptomatic, conservative treatment is usually performed. When the lesion begins to cause cosmetic deformities or discomfort, then more invasive forms of treatment can be considered. DSA should be performed before treatment is considered to identify whether the SP follows the dominant or accessory pattern of drainage. Since dominant SP is the main outflow of the intracranial venous system, treatment could potentially lead to cerebral hemorrhage, intracranial hypertension, or death. Thus, dominant SP is generally not treated. Contrastingly, accessory SP can be safely treated because it does not significantly contribute to the intracranial venous outflow.
The two main forms of treatment used for treatment of SP consist of endovascular therapy or surgery. Endovascular embolization is generally effective and safer than surgery for treatment of SP. It may still result in complications such as embolism and skin necrosis, but the treated patients had faster recoveries, less blood loss, and lower infection risk. Surgery is also an option; however, it carries more risks and is more so reserved for more complicated forms of SP.
The prognosis of SP is generally very good, and the typical course commonly shows no further evolution in size after puberty and low risk of spontaneous or traumatic bleeding. There have been described cases in the literature of spontaneous involution or partial thrombosis.
In summary, clinicians should be aware of the clinical and radiographic features of SP. Although many patients with SP are asymptomatic, some require treatment.
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