Sinus pericranii

Sinus pericranii also called subgaleal varix, is a rare venous anomaly characterized by an abnormal communication between the intracranial and extracranial veins through a bone defect ¹. It is usually located near the dural sinuses and presents as a soft, palpable scalp mass ². In sinus pericranii there is an abnormal communication between intracranial dural sinuses and extracranial venous structures, usually via an emissary transosseous vein. Sinus pericranii is considered a type of low flow vascular malformation. It occurs in close communication with the cranial vault and most frequently involves the superior sagittal sinus. Pathologically, it exhibits a direct communication between the nonmuscular veins adhering to the outer surface of the skull and the intracranial venous sinuses ³.  The distribution of the lesions is more commonly found in the frontal region (43%), followed by parietal (36%) and occipital regions (7.4%) ⁴. A lateral location is unusual ⁵.

Sinus pericranii patients may present with mild (local pain, nausea, headache, and dizziness) to severe (increased intracranial pressure, bradypnea, bradycardia, ataxia, hearing loss, and epileptic seizures) symptoms ⁶. However, most cases are asymptomatic, with the main complaint being the associated cosmetic problems ⁷. Additionally, considering its clinical presentation, it is imperative to identify sinus pericranii from other diseases presenting as a mass on the scalp and it is vital to avoid harmful biopsy because of the communicating venous anomalies ⁸. When suspected on radiological basis, a simple clinical test can be performed. Unless thrombosed, the sinus pericranii will appear more prominent on supine position than when sitting, because of variable venous pressure with gravity. The lesions are not classically associated with discoloration of the overlying skin.

Sinus pericranii can be congenital (present at birth), in which case it is often obvious, but may also be acquired through trauma or iatrogenic and might be subtle in these cases. Most of sinus pericranii is a congenital type, which formed at late embryogenesis. After birth, the lesion which has been for several years can have a typical feature of pathologic findings. The existence of thick accumulated stroma suggested a possibility of congenital type sinus pericranii. On the other hand, acquired type sinus pericranii usually depicts fibrous microstructure encapsulating the blood. This is because trauma disrupts emissary veins and calvarium, making a fibrous lining or capsule around the extravasated blood.

Sinus pericranii has been defined as a varix and classified into three types according to the size of the venous communication between the extracranial blood sac and intracranial venous sinus ⁹. Newton and Troost ¹⁰ described it as a communication between the extracranial and intracranial venous circulation via large, tortuous, thin walled vascular channels. Volkmann described two types of sinus pericranii : ‘true sinus’ which fills with increased intracranial pressure and disappears completely with compression and ‘pseudo sinus’, which fails to disappear completely with compression. They considered the latter to be angioma or cavernoma of mainly venous component.

Since it is a venous anomaly, it can be diagnosed with methods similar to those used for other venous anomalies in the head and neck region. Doppler ultrasonography is a useful radiological tool to differentiate different vascular anomalies ¹. Following which, MRI can be used to characterize the size and extent of the lesion. T2-weighted MRI shows a mass with high levels of mixed signals, which includes a signal void due to the blood flow ¹¹. Some authors recommend direct percutaneous venography as a confirmatory tool ¹², however, it is associated with a high risk of bleeding and infarction.

Because most sinus pericranii has benign features, asymptomatic sinus pericranii can be observed or conservatively treated ¹³. Although spontaneous regression of sinus pericranii has been reported ¹⁴, most patients require removal of the sinus and blocking the communicating veins. Cosmetic reasons remain the main indication for surgery in sinus pericranii ¹⁵. However, all symptomatic sinus pericranii cannot be actively treated. Using the venous drainage pattern, sinus pericranii can be classified into a dominant type or an accessory type ¹⁶. The dominant type of sinus pericranii is defined when a majority of the venous outflow occurs through the sinus pericranii. Meanwhile, when only a small portion of the venous drainage flows through the sinus pericranii, it is called as the accessory type. In the dominant sinus pericranii, active treatment should be avoided because of the consequential venous infarction and bleeding ¹⁵. On the contrary, the accessory type of sinus pericranii can be treated by surgical resection or endovascular embolization ¹⁷. Some reports suggest that surgical excisions for sinus pericranii could be considered in the presence of neurologic symptoms, psychological discomforts, dermatological changes, patient’s wishes, and coexisting morbidity. Additionally, coexisting morbidities included syndromic craniosynostosis, additional vascular anomalies, meningocerebral anomalies, and systemic anomalies or malformations ⁶, ⁷. The occlusion of this abnormal pathway has not been reported to result in intracranial venous hypertension ¹⁸.

Figure 1. Sinus pericranii

Footnote: (A and B) Front and top view show a well-defined blue plate, located in the medial frontal area, the patient underwent surgery with complete removal of the sinus pericranii. (C) MRI demonstrating a sinus pericranii.

[Source ¹⁹ ]

Figure 2. Sinus pericranii radiology

Footnote: MRI T2 weighted images (sagittal) and (frontal) shows venous communication between a cortical dilated vein and the superior sagittal venous sinus with bulging of the subcutaneous tissues that conditions a mass effect in the midline.

[Source ¹⁹ ]

Figure 3. Sinus pericranii

Footnote: A 2-year-old girl with sinus pericranii was brought to the hospital due to an apparent disfigurement and bluish skin in the right periorbital region and a soft mass-like diffuse lesion on the scalp. The lesion was non-pulsatile and bluish, and the patient did not complain of pain. (A) Venous malformations in the right periorbital region are seen on the frontal view. (B) Vascular masses on the scalp are also seen.

[Source ¹ ]

Sinus pericranii causes

Sinus pericranii etiology is not fully elucidated. It is divided into three types: congenital, spontaneous, and posttraumatic ²⁰. After trauma and cranial injuries, rich vein circulation in the skin and intracranial cavity can cause sinus pericranii ²¹. Sinus pericranii can spontaneously occur when there is erosion in the skull caused by increased intracranial pressure1 ²². If sinus pericranii is congenital, incidence of sinus pericranii increases with other vascular pathologies such as venous angioma, aneurysmal malformations, internal cerebral vein, and cavernous hemangiomas. Thus, all cerebral vascular pathology should be considered in patients diagnosed with sinus pericranii ²³.

Heinke ²⁴ stated that vomiting, forceful coughing, respiratory disturbances and other such forces might cause tearing of emissary veins at the bone surface eventually resulting into a communicating blood cyst on the skull surface. Cohn ²⁵ stated that the endothelial lining of the wall of the sinus pericranii differentiates the congenital type from the acquired type. Most cases of sinus pericranii are located near the midline. The frontal region is most frequently involved followed by the parietal region ⁹. Frontal sinus pericranii with an orbital extension has not been reported in the literature. Usually the patients are not symptomatic and the problems are cosmetic. Rarely there may be headache, giddiness and vertigo.

Sinus pericranii may be part of a syndrome in some patients, but can occur as an isolated condition. Associations with craniosynostosis, Crouzon’s syndrome, Apert’s syndrome and Hunter’s syndrome are well documented ²⁶.

Sinus pericranii differential diagnosis

Sinus pericranii differential diagnosis includes arteriovenous malformation, epicranial varix, cavernoma, growing skull fracture, eosinophilic granuloma, epidermoid tumour, dermoid, meningocele and encephalocele.

Sinus pericranii symptoms

Most sinus pericranii patients visit their doctor primarily complaining of the mass on the scalp. The distribution of the lesions is more commonly found in the frontal region (43%), followed by parietal (36%) and occipital regions (7.4%) ⁴. A lateral location is unusual ⁵. Some sinus pericranii patients may present with mild (local pain, nausea, headache, and dizziness) to severe (increased intracranial pressure, bradypnea, bradycardia, ataxia, hearing loss, and epileptic seizures) symptoms ⁶. The main concern is usually cosmetic due to the bulging nature of the malformation. The sinus pericranii are reported to be associated with vascular malformation, haemangioma of the cerebellum or retina as a part of the von Hippel-Lindau syndrome, blue naevus syndrome, venous cavernoma of the scalp and hemangioma of the tongue.

Coexisting diseases associated with sinus pericranii have been reported, such as cerebellar venous angioma ²⁷, blue rubber bleb nevus syndrome ²⁸, arteriovenous malformation ²⁹, dural sinus malformation ²⁹, vein of Galen aneurysmal malformation ²⁹, cavernous hemangioma ³⁰, aneurysmal malformation of the internal cerebral vein ³¹, vein of Galen aplasia ²⁹, PHACE syndrome ³², craniosynostosis ³³, and subcutaneous venous cavernoma ³⁴.

Sinus pericranii complications

The occurrence of thrombosis is common in sinus pericranii because of the slow flow of blood within the sinus pericranii as well as the common occurrence of thrombi within venous malformations elsewhere in the body ³⁵. If dominant venous drainage had been affected by trauma or thrombosis, a life-threatening complication may occur, such as venous congestion and/or infarction, brain swelling, or hemorrhage. The possible complications during surgery are hemorrhage and air embolism ⁹.

Awareness of both the patency and direction of flow in a dominant emissary vein is important for preventing life-threatening complications during surgery. Although intraoperative cerebral angiography or indocyanine green video-angiography can be used to evaluate the venous flow, these are invasive methods that only provide intermittent monitoring. Alternatively, ultrasonography is non-invasive and inexpensive relative to other imaging modalities, and can provide continuous evaluation of venous flow during surgery. As in the present case, ultrasonography can also detect extracranial venous tubular structures and visualize the emissary vein. Moreover, color Doppler ultrasonography can confirm venous flow in these tubular structures and reveal both the direction and pattern of venous flow in the emissary vein ³⁶. Recent advances in technology have yielded a variety of ultrasonography probes suitable for diverse operative situations.

Sinus pericranii diagnosis

The diagnosis of sinus pericranii can be made by the appearance of soft, fluctuant mass located near the intracranial sinus, which usually vary in size with change in the intracranial pressure. Confirmation of sinus pericranii can be identified by various imaging techniques such as CT scan, MRI and Doppler ultrasonography. CT scanning allows direct visualization of the bony defect. MRI with or without MR angiography is believed to be of great benefit at providing a definitive diagnosis of sinus pericranii and its drainage into the dural sinuses ³⁷. Angiography can separate sinus pericranii into two patterns; dominant and accessory.

Sinus pericranii treatment

There is little available evidence with regards to available guidelines and recommendations concerning the management of  sinus pericranii ¹⁵. Previous reports on sinus pericranii included surgical treatment, endovascular embolization, and conservative treatment ²⁰, ⁶, ³⁸, ³⁹, ⁴⁰, ⁴¹. A recent retrospective study by Pavanello et al ⁴², looking at the diagnosis and management in 21 pediatric patients, suggests that only accessory sinus pericranii is amenable to treatment, whereas dominant sinus pericranii must be preserved due to its potential life-threatening complications associated with it, such as hemorrhage and venous congestion.

Endovascular approach to treatment has proven to be safe and effective when treated for cosmetic reasons, in cases of accessory sinus pericranii. Digital subtraction angiography has proven to be effective in excluding other vascular malformations as well as assessing the intracranial venous dynamics and their relationship to the sinus pericranii ⁴³. While this has been rarely reported in the available literature, endovascular embolisation appears to have good results when patients are identified for potential complications ⁴⁴. This method of managing sinus pericranii is less invasive than surgery but still carries the risk of causing skin necrosis and embolic events ⁴⁵.

Surgical management has been demonstrated in a retrospective study conducted by Park et al ⁴⁶ where 10 patients underwent operations for sinus pericranii. All patients with sinus pericranii associated with craniosynostosis were managed conservatively. This study concluded that surgery can be performed in cases without intracranial venous compromise. Surgery can be safely carried out with thorough preoperative planning and imaging of the cranial vault.

Conservative management has rarely been reported in the literature with regards to follow-up. One case reports the case of a 6-year-old who was safely managed through this method ⁴⁷. Surveillance proved an effected method of monitoring the condition, with no reported complications. Another retrospective study identified four patients with untreated accessory sinus pericranii, two of which resolved spontaneously, one was lost in follow-up and the remaining one was unchanged.

Sinus pericranii prognosis

Due to sinus pericranii rarity, its pathogenesis and natural history remains unclear. The long-term outcomes of sinus pericranii are poorly understood ¹⁵.

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