Teaching Case

A 16-year-old adolescent girl presented with complaints of left cheek swelling for the past 2 years, increasing in size in the dependent position. On clinical examination, a soft tissue bulge was seen on the left side of the face, which was compressible and soft on palpation. No overlying skin discolouration was seen.

Ultrasound of the left cheek revealed an ill-defined hypoechoic lesion with few cystic areas and echogenic foci, giving posterior acoustic shadowing (Figure 1a). Mild internal vascularity was seen with slow flow venous waveform (Figure 1b). CEMRI (Contrast Enhanced Magnetic Resonance Imaging) of the face was obtained for better characterisation and to assess the lesion extent. MRI revealed an ill-defined, lobulated, trans-spatial, T2 hyperintense lesion on the left cheek and in the masticator muscles (Figure 2). On dynamic contrast-enhanced MR sequences, gradual filling with contrast was seen during the course of examination (Figure 3). The lesion was extending into the extraconal compartment of the left orbit and reaching up to the temporal fossa superiorly (Figure 2). In the appended sections of the brain, absent flow-related enhancement was noted in the cavernous and petrous segment of the right internal carotid artery (ICA) (Figure 4), and a dedicated CT angiography of the head and neck was hence obtained. CT of the head and neck showed a soft tissue lesion on the left side of the face with multiple phleboliths. CT Angiography revealed a relatively decreased calibre of right CCA compared to the left side and continuation of the right common carotid artery (CCA) into the external carotid artery (ECA). Right ICA was not visualised in its entirety, including the cervical and cranial segments with a rudimentary right carotid canal (Figures 5 and 7).  The right middle cerebral artery (MCA) was supplied by the hyperplastic right posterior communicating artery (PComm), while the right anterior cerebral artery (ACA) was supplied by the anterior communicating artery (AComm) (Figure 6).

Background

Dysgenesis of ICA is a rare anomaly with an estimated prevalence of 0.01% [1,2]. ICA dysgenesis may involve a segment or whole of ICA and can present in the form of agenesis (complete absence with no vascular remnant), aplasia (complete absence of artery with the presence of vascular remnant), or hypoplasia (attenuated calibre of ICA). The atretic carotid canal helps to distinguish ICA agenesis from aplasia or acquired causes of ICA occlusion [1–3]. Agenesis of ICA is related to embryological insult during the development of 1^st and 3^rd aortic arches.

On the other hand, vascular malformations are lesions of vascular dysmorphogenesis that are characterised based on their flow characteristics. The ISSVA classification system further categorises them as simple or combined malformations and whether the lesions occur in isolation or in association with syndromes [4]. The head and neck are common sites for vascular malformations, with slow-flow vascular malformations being more common than high-flow malformations. They are congenital lesions and tend to grow in late childhood or early adulthood [5]. It is still unclear whether the co-occurrence of vascular malformation is attributable to the hemodynamic alteration due to the existing vascular anomaly, compensatory elevation of endothelial growth factors, or chance finding alone.

Clinical Perspective

Patients with ICA agenesis are rarely symptomatic because of collateral supply, which may come from contralateral cerebral vessels, vertebrobasilar system, persistent fetal vessels, or from transcranial ECA collaterals. There is increased incidence of aneurysm formation in the contralateral vascular bed in patients with ICA agenesis, likely due to hemodynamic flow alterations. In a study by Kumar et al, they described a case of cerebral AVM contralateral to the side of agenesis [6]. However, there has been no case reported to date showing ICA agenesis with contralateral vascular malformation in the face.

Imaging Perspective

MRI is the imaging modality of choice for the complete evaluation of vascular malformations. Venous malformations, a type of slow flow malformation, as seen in our case, reveal ill-defined, T2 hyperintense soft tissue lesions showing variable gradually progressive post-contrast enhancement. On Dynamic post-contrast sequences, there is lack of early arterial enhancement, lack of enlarged draining veins or arterial feeders and absence of AV shunting, thus distinguishing them from high flow vascular malformations.T1/T2 hypointense foci showing blooming are suggestive of phleboliths and almost pathognomic of venous malformations [5]. Ultrasound can be a valuable adjunct to MRI. However, for extensive lesions, MRI is preferred. On US, venous malformations are characterized by ill-defined hypoechoic lesions with a few cystic spaces and, on color Doppler, slow monophasic flow is seen [5]. CT angiography of the head and neck is the modality of choice for the workup of patients with suspected vascular anomalies, which in our case revealed the absence of right ICA and atretic carotid canal. Lie described the six types of collaterals for the supply of the MCA and ACA ipsilateral to the side of agenesis, which broadly stem from contralateral cerebral vessels, vertebrobasilar system, persistent fetal vessels, or from transcranial ECA collaterals [3,7]. MCA supplied via hypertrophied ipsilateral PComm and ACA via AComm is the most common type, as seen in our case.

Outcome and Teaching Points

Patients with ICA agenesis are generally asymptomatic and do not require treatment. Routine surveillance by MR Angiography can be offered to rule out intracerebral aneurysms. Dynamic CEMRI is the modality of choice for the diagnosis of vascular malformations, with ultrasound being a useful adjunct. Venous malformations, if symptomatic, can be treated with a multidisciplinary approach, which includes sclerotherapy, surgical excision, ablation, or pharmacotherapy.

The co-occurrence of ICA agenesis with venous malformation of contralateral face is exceptionally rare. The possibility of any causal association between the two entities is yet to be ascertained.

All patient data have been completely anonymized throughout the entire manuscript and related files.