Teaching Case

A 5-year-old boy presented to the paediatric clinic with a parietal cranial soft tissue mass present since birth. The mass had become progressively sore and increased in size. The patient had no significant medical history, other complaints, or neurological deficits.

Ultrasound showed a small hypoechoic soft tissue mass with increased colour Doppler activity, laterally to the sagittal suture (Figure 1a). In supine position, after 5 minutes, the protrusion increased in size and showed no colour Doppler activity (Figure 2a).

A subsequent MRI showed a subcutaneous, well-defined, extracranial soft tissue mass parietally in the midline (Figure 2a). There was an intermediate signal intensity on T1-weighted sequence and a high signal intensity on T2 and FLAIR. On T2 weighted images and FLAIR, the lesion showed multiple signal voids, probably representing venous flow voids (Figure 2a). There was scalloping of the outer table of the underlying skull.

Intravenous contrast showed strong enhancement in part of the lesion. Several small emissary veins were seen extending into the soft tissue lesion through the calvarium near the superior sagittal sinus, although no definite connection to the superior sagittal sinus could be identified (Figure 2c).

Sinus pericranii is a rare vascular anomaly characterized by dilated extracranial veins communicating with dural sinuses by way of transcalvarial emissary veins. Sinus pericranii can be either congenital or rarely acquired as a result of trauma [1].

Sinus pericranii is commonly identified during infancy or early childhood. At birth, children with sinus pericranii often present with an extracranial non-pulsatile soft tissue mass. Intracranial pressure affects the anomalous vessels, e.g., they increase in size when in supine position. Most patients are asymptomatic; however, some experience headaches, nausea, vertigo or local pain [1].

Sinus pericranii has several differential diagnoses: pseudomeningocele, dermoid cysts, haemangiomas, arteriovenous malformations, etc. Due to the many differential diagnoses, clinicians often need diagnostic imaging to make the diagnosis [1].

Several modalities are used in imaging masses on the skull [1]. CT without contrast can show an enhanced soft-tissue mass above the skull [2]. Ultrasound may show a hypoechoic mass superficial to the skull that increases in size in supine position. Utilizing colour Doppler can help in identifying the presence of blood flow between the mass and the intradural venous system [3]. An MRI may demonstrate mixed signal intensity soft-tissue masses with areas of blood flow. Contrast-enhanced MRI can show communication between the transcalvarial veins and the superior sagittal sinus, confirming the diagnosis [4]. The gold standard for sinus pericranii diagnosis is cerebral digital subtraction angiography [1], but these are invasive and ideally not performed in children.

The prognosis of sinus pericranii is generally favourable, as after puberty, most cases show no change in size [1]. Sinus pericranii can rarely give rise to life-threatening complications stemming from infection or significant scalp haemorrhage [2].

Typically, surgery is offered due to cosmetic complaints rather than dangerous complications [5]. Surgical treatment aims to restore cosmetic appearance and prevent complications. The approaches used are: craniotomy, to excise both the extracranial and intradural lesions; local scalp incisions, to plug the bony venous channels; or endovascular embolization, as a definitive treatment. However, long-term effectiveness of embolization is uncertain [1]. In this case, the neurosurgeon opted for watchful waiting due to the patient’s mild symptoms and risks associated with the procedure.

Sinus pericranii is a rare disorder with a favourable outcome and mild symptoms, if not completely asymptomatic. While clinical suspicion may arise for sinus pericranii, imaging is needed to confirm the diagnosis [3].