Introduction

Sinus pericranii (SP) is a rare vascular anomaly, usually asymptomatic condition, characterized by a congenital or acquired epicranial blood-filled nodule of the scalp. It has an abnormal venous communication between the extracranial and intracranial circulatory system via the dipole of the skull, which usually involves the superior sagittal sinus and sometimes the transverse sinus. SP is generally considered to be a congenital anomaly, but some cases have been attributed to trauma, or to an unusual stress or strain. We report a case of SP in an 20-year-old female following a minor head trauma.

Case Rrport

A 20-year-old female presented with intermittent headache for several years. She had a soft, painless, non-pulsatile, round scalp mass of 2¡¿3cm in the left retroauricular area. There was a history of minor head injury, and she first noticed the scalp mass about a month after the trauma. The size of the mass was reduced by manual compression. The mass expanded on supine position and it became tense on Valsalva maneuver, or by bilateral jugular vein compression, but it disappeared when she sat up. The skin over the swelling looked grossly normal and there was no transillumination. The plain skull radiograph showed only round bony erosions. The computed tomography (CT) scan demonstrated an extracranial mass with heterogeneous enhancement above the bony erosion of skull (Fig. 1). In addition, magnetic resonance imaging (MRI) showed isointensity on T1-weighted and hyperinstensity on T2-weighted images, and the mass was heterogeneously enhanced with connection to the diploic layer (Fig. 2). The arterial phase of cerebral angiography showed no abnormal findings, but the venous phase showed a pericranial varicosity of diploic veins directly communicating with the superior sagittal sinus. The rest of the cortical veins showed no abnormality (Fig. 3). The patient was diagnosed as SP and underwent a surgery. The lesion was located under the galea and there were small vascular channels which could be obliterated completely with bipolar coagulator and bone wax (Fig. 4). The patient was treated without performing a craniotomy. Postoperative course of the patient was uneventful. The headache subsided and the scalp swelling disappeared. The follow-up angiography revealed no abnormal venous vasculature (Fig. 5).

Discussion

SP is a rare congenital or acquired disease entity that is characterized by abnormal extracranial vascular structures with direct communication to intracranial dural sinuses via dilated emissary or diploic veins of the skull. This vascular anomaly was first described by Hecker in 1845 as Ôvarix spurious circumscriptus venae dipoicae frontalisÕ,2)6) and was referred by Stromeyerin in 1850 as a Ôsubperiosteal blood-filled cyst of the skull communicating with an intracranial sinusÕ and the term Ôsinus pericraniiÕ was first proposed.19) Several authors have proposed classification schema to distinguish various subtypes according to the size of the defect,21) the pathophysiology, and circulation patterns,4) and underlying cause.11) The etiology of SP is unknown. 3 possible causes have been postulated with regard to pathogenesis of SP which are congenital, spontaneous, and traumatic. The main difference between congenital and acquired SP is the presence of an endothelial lining at the wall of the SP.2) The traumatic type is usually related to a minor injury. Spontaneous SP may also be related to an unnoticed or forgotten trauma, so some of spontaneous types may actually belong to the traumatic types. It is also possible that subclinical congenital lesion expand as a result of head trauma. Even with these controversies, many cases showed the pathological findings of vascular tissue lined with endothelial cells at the wall of the SP on microscopic examinations, and so the congenital theory is widely accepted.

In most patients, it is located near the midline. The frontal region is most frequently involved followed by the parietal and the occipital region.2)14) Although the reason for the frequent occurrence near the midline has not been clarified in the previous literatures, it is logical to think that this vascular anomaly may have tendency to occur near the major venous drainage which usually is the superior sagittal sinus. As in our study, a lateral location with venous drainage not to the transverse sinus but far away to the superior sagittal sinus seems to be an extremely uncommon case.

Headache, sensation of pressure or fullness, localized pain, vertigo, and nausea are common manifestations in symptomatic patients. Typically, this anomaly appears to be a soft fluctuating mass located near the intracranial sinus which disappears if the patient is in upright position. On the other hands, the SP enlarges with the maneuvers that increase intracranial pressure, such as coughing, compressing jugular veins bilaterally, or performing Valsalva maneuver. These clinical features demonstrated by manual and hemodynamic maneuvers on physical examination are the only clues to make an impression of SP. However, these findings are often neglected by physicians, and a crude surgical attempt without any radiological evaluation will obviously lead to a tragic event during operation. In the past, SP was diagnosed mainly by invasive angiographic studies such as sinography, direct injection of contrast media into the mass, and digital subtraction angiography.9)18) With the recent development of non-invasive imaging techniques, CT, 3D-CT, and MRI with or without MR angiography or MR venography can also provide a definitive diagnosis of SP. In our case, MRI with MR angiography and cerebral angiography clearly demonstrated the communication between the mass and the dural venous sinuses via diploic veins and enlarged superficial cortical veins.

Extensive disease entities can be put into the differential diagnosis because several congenital and post-traumatic scalp lesions can mimic SP, and they are subepicranial varix, venous cavernoma, arteriovenous fistula, traumatic leptomeningeal cyst, cephaloceles (meningocele, meningo-encephalocele, and meningo-myelocele), dermoid tumor, eosinophilic granuloma, hemangioma, meningioma, and so forth.

Although SP is usually asymtomatic and spontaneous regression has been reported,8) it can be treated surgically for the cosmetic reasons and for the prevention of infection, air embolism after trauma, and spontaneous rupture or massive bleeding.2)18) Only a few reports have mentioned the spontaneous regression of SP. Carpenter JS et al reported spontaneous partial thrombosis of SP in 2 patients after conservative management with non-steroidal medication and warm compression.5) Rozen WM et al reported complete radiological resolution of SP in a 7-week-old patient by 18 months.15) In our case, a definitive treatment such as surgical excision was preferred since the patient suffered for several years from headache along with a significant cosmetic deficit from fluctuating mass. Some different surgical procedures to correct SP lesions have been reported. Craniectomy of involved skull with division of the diploic veins followed by cranioplasty has been described as a radical operation.2)18) Recently, removal of the extracranial mass and closure of the emissary veins using bone wax, gelform packing, coagulation, and diamond-drilled bony dust, if possible, to plug the bony holes have been thought to be adequate to prevent recurrence.1) Endovascular surgery for sinus pericranii also has been described.3)4) In this case, we removed the mass en bloc after coagulating collateral veins of scalp and then bleedings from multiple small communicating diploic holes were controled by diamond-drilling and bone wax packing instead of performing a craniotomy.

Conclusion

SP is a rare vascular anomaly and is often misdiagnosed. The appropriate physical examinations and radiographic studies are necessary to make correct diagnosis prior to any surgical attempts. Thorough preoperative evaluations will prevent fatal complications from unexpected intraoperative bleedings.