A Rare Presentation of Suspected Temporal Bone Arteriovenous Malformation in Pregnancy

Arteriovenous malformations (AVMs) are most frequently observed in craniofacial bones, with a predilection for teeth-bearing bones (7).  They are rarely affecting the temporal bones (8).   They may occasionally arise following trauma but more generally develop as congenital aberrations of localised vasculogenesis during the early embryonic period.   They usually remain dormant and unnoticed during childhood and only become symptomatic during rapid growth phases elicited by puberty or pregnancy hormonal changes (9).  As AVMs are benign, treatment revolves around symptom management and mitigating potential complications such as unabated growth, disruption of adjacent tissue structure, and haemorrhage secondary to vascular failure.   Factors that may affect management decisions include the size and location of the AVM, particularly if involving the face or neck, and the presence of co-existing medical or congenital conditions that may predispose the patient to multiple lesions or an elevated risk of complications such as haemorrhage (10, 11).

Physiological adaptations in pregnancy, particularly those of the cardiovascular system, which include expansion of blood volume to support the increased cardiac output necessary for foetal growth, are particularly significant provocateurs (12).  While instances of intracranial haemorrhage secondary to AVMs are uncommon, when they do occur, they often do so in the third trimester or at the time of delivery when changes to cardiovascular health are maximal.   During labour, the risk of haemorrhage is heightened by hypertensive episodes associated with pain and the work of pushing and the episodic tidal floods of venous filling that occur with uterine contractions.  Patients with underlying vascular disease, either pre-existent or acquired as comorbidities during pregnancy, such as diabetes, hypertension or pre-eclampsia, may be particularly susceptible (2,3).

There is no definitive consensus on the effective management of pregnant women with AVMs.  A review reported that AVM haemorrhage was significantly associated with poor maternal outcomes, specifically neurological disability (3).  Owing to the potential risk of treatment and resultant risk–benefit analysis, routine active AVM treatment during gestation is not universally advocated (2,3 & 6).  Should intervention be necessary, it is typically scheduled for no later than the second trimester.  Active AVM therapeutic modalities include surgical resection, endovascular embolization, or stereotactic radiosurgery (such as gamma knife).  (2,4).  The most commonly employed and comparatively more accessible procedures include embolization and sclerotherapy.

Embolization entails using materials such as medical glue, metal coils, or plugs to impede blood flow within an AVM, introduced via a catheter into an artery connected to the AVM.  Conversely, sclerotherapy injects obliterative agents into an AVM, instigating scar formation and destructive effects on the feeder vasculature.  As these techniques do not eliminate the AVM, there remains a risk of AVM re-expansion post-treatment.  Treatment options for temporal bone AVMs must be selected judiciously, with due consideration given to the potential risks to the facial nerve.

In cases of unruptured AVMs during pregnancy, conservative observation may be adopted, provided there are no precipitating factors for bleeding, such as hypertension, co-existing aneurysm, or venous ectasia.  There is limited evidence addressing whether the risk of cerebral AVM haemorrhage is increased with vaginal delivery or mitigated by caesarean section.  Irrespective of the delivery method, meticulous blood volume and pressure control are crucial to minimise the risk of rupture (13).