Severe Anemia as a Rare Complication of Traumatic Scalp Arteriovenous Fistula: A Case Report

Introduction

Arteriovenous fistulas (AVFs) are abnormal connections between arteries and veins that bypass the capillary bed. Despite the rich vascularization of the scalp and the high incidence of head injuries, traumatic scalp AVFs remain rare [1]. Most are not life-threatening and are primarily of cosmetic concern [2,3], but severe complications, including ulceration [4] or hemorrhage [5], can occur.

We report a case of an acquired traumatic AVF of the scalp. The patient developed chronic anemia due to repeated bleeding from fragile arteriovenous connections. The AVF resulted from domestic violence, and friction of the lesion against a pillow during sleep likely contributed to ongoing bleeding. The patient exhibited prolonged physiological compensation to chronic blood loss, highlighting the potential for delayed recognition in the Emergency Department (ED), where more common sources of bleeding are typically considered first.

This case emphasizes the diagnostic value of a structured SAMPLE (symptoms, allergies, medications, past medical history, last meal, events leading up to the injury) and ABCDE (airway, breathing, circulation, disability, exposure) assessment, including a thorough skin examination. Prompt imaging, particularly computed tomography (CT) angiography, is essential to identify vascular lesions and guide management, which in this case involved embolization of the fistulous vessels.

Furthermore, it highlights the importance of formulating a broad differential diagnosis for anemia and soft-tissue masses, while illustrating gaps in current guidelines for the assessment and management of traumatic AVFs.

Case Report

A 38-year-old woman was admitted to the ED due to head injuries, secondary to domestic violence. The patient’s main concern was a persistently bleeding scalp mass. History collected in SAMPLE format revealed 6 months of progressive generalized weakness and a history of alcohol dependence syndrome and alcohol-related epilepsy (treated with valproic acid 500 mg twice daily and hydroxyzine as needed). She denied having any allergies and reported multiple prior head trauma secondary to assault.

ABCDE-based examination revealed skin pallor and a pulsatile scalp mass in the occipito-parietal region, which according to the patient had been present for the past 4 months (Figure 1). The patient reported daily recurrent bleeding of varying intensity from the mass, which persisted for 3 months. She stated that it was sometimes profuse enough that, after a night’s sleep, blood had soaked through the dressings onto her pillow. She noted that on most mornings the head dressing was saturated with blood. She added that the scalp bleeding intensified and was accompanied by localized pain each time she flexed her neck forward.

The patient’s medical records revealed multiple admissions to the ED. Her first documented ED visit occurred 7 months earlier, during which an open head wound was documented, and a non-contrast CT scan revealed bilateral scalp hematomas in the parietal regions. Apart from asymptomatic anemia (hemoglobin [Hb] level was 10.4 g/dL; reference range 12–16 g/dL), no other abnormalities were noted. After observation, she was discharged home with instructions to follow up with her primary care physician regarding the wound.

Four months ago, she returned to the ED with a new pulsatile scalp mass in the occipito-parietal region but left before a comprehensive evaluation could be performed. She returned 2 days later, at which point the mass was no longer pulsatile; she did not report any pain and no bleeding was observed. She was then referred to the General Surgery Department. Due to her stable condition and the absence of alarming symptoms, no surgical intervention was undertaken. At that time, she had asymptomatic anemia (Hb 8.2 g/dL; reference range 12–16 g/dL). She was advised to use head dressings in case of bleeding and was scheduled for further follow-up in the surgical outpatient clinic.

Due to the patient’s history of progressive decline in Hb levels (10.4 g/dL 7 months earlier and 8.2 g/dL 4 months earlier), a point-of-care arterial blood gas analysis was performed during the current admission. It revealed Hb concentration of 3.7 g/dL (reference range 12–16 g/dL), prompting transfusion of 5 units of red blood cells. A differential diagnosis work-up for the cause of anemia was subsequently initiated.

A per rectum examination, gastroscopy, sigmoidoscopy, abdominal and retroperitoneal ultrasound, and chest X-ray were performed, none of which identified a source of bleeding. Trauma and hemorrhage from natural body orifices were excluded, and the patient denied any history of vaginal bleeding. Fluid overload, hemolysis and disorders of erythropoiesis were also ruled out. No evidence of infection, autoimmune disease, or malignancy was noted.

Laboratory studies, including a complete blood count (CBC), prothrombin time (PT/INR), activated partial thromboplastin time (aPTT), and fibrinogen levels, excluded coagulopathies and other systemic causes of bleeding.

In the differential diagnosis of the scalp lesion, a soft-tissue tumor (eg lipoma, epidermoid cyst, dermatofibroma) was initially considered but excluded based on the lesion’s vascular features (eg, pulsation) and the history of recurrent bleeding. To evaluate a possible vascular etiology (eg, hemangioma, venous malformation, AVF), a CT angiography of the cerebral arteries was ordered in the ED (Figure 2A, 2B). It revealed numerous tortuous, dilated subcutaneous vessels in the left parieto-occipital region, which were consistent with a vascular malformation in the form of an AVF. The pathological vessels were primarily supplied by a mildly dilated left occipital artery (OA) and, to a lesser extent, by the parietal branch of the left superficial temporal artery (STA). Venous drainage occurred through the superficial temporal vein, which emptied into the retromandibular vein. For improved visualization of the vascular anatomy, volume-rendered reconstructions were generated (Figure 3A, 3B).

Next, the patient was consulted by a neurosurgeon and was subsequently referred to the Department of Vascular Surgery. There she received an additional 2 units of packed red blood cells and was later transferred to a vascular surgery center with greater experience with managing AVFs.

The definitive treatment of the AVF included embolization of the OA and STA. Coils were initially used to reduce blood flow through the fistula, followed by an injection of absolute alcohol to achieve permanent obliteration of the pathological vascular channel. In addition, to prevent recurrence and improve the aesthetic outcome, surgical excision of the lesion and an autologous skin graft were planned, but the patient did not consent to these 2 procedures. Treatment was therefore considered complete.

Discussion

This case highlights several key aspects of traumatic scalp AVFs relevant to clinical practice. Even minor head trauma can result in delayed AVF formation, emphasizing the need for prolonged vigilance. CT angiography can provide rapid assessment of lesion extent and vascular supply in ED settings. The case also illustrates a rare complication: chronic anemia due to persistent bleeding without acute rupture. Finally, definitive treatment (whether via embolization, surgical excision, or both) can prevent complications and improve outcomes; in the present case, embolization alone controlled fistula flow and resolved the patient’s symptoms.

Although CT angiography provided sufficient diagnostic information, digital subtraction (DS) angiography might have allowed more precise characterization of minor feeding vessels. Embolization successfully controlled the fistula flow, and because the patient declined the surgical excision, it was considered definitive treatment. However, the long-term risk of recurrence and subsequent bleeding remains uncertain.

Historically, AVFs have been described using various terms [6,7], but in this case report we used “arteriovenous fistula”. They are pathological connections between the external carotid artery (or its branches) and subcutaneous scalp veins, forming either a single artery-to-vein fistula or a complex nidus [8,9]. They occur across frontal, temporal, parietal, and occipital regions [4], and arterial compression can reduce the surrounding edema [1]. Etiologies include trauma, iatrogenic procedures, aesthetic interventions, and idiopathic causes [6,8–11]. Clinically, a scalp AVF typically presents as a pulsatile, tender and swollen mass, which can lead to headaches [12], tinnitus [2,9,13–15], or even epilepsy [16].

Blunt head trauma can cause immediate scalp swelling from subcutaneous hematoma, which usually resolves spontaneously. However, in rare cases, the lesion can enlarge and pulsate, potentially leading to chronic subdural hemorrhage. A less common cause of this clinical picture is a pseudoaneurysm or an AVF [13]. These diagnoses can be differentiated through physical examination, patient history, and imaging studies.

AVFs alter the original hemodynamics of the vessels, causing varying degrees of damage to the surrounding tissues depending on the lesion’s location [17]. The flow of high-pressure arterial blood into the venous system leads to enlargement of the vascular bed, potentially causing a visible subcutaneous deformity [2,6,8].

Scalp AVFs remain rare [1], with fewer than 50 cases reported in the literature [13]. They account for approximately 8.1% of all arteriovenous malformations [16].

Two main hypotheses explain traumatic scalp AVFs formation. The first suggests that injury to the arterial vasa vasorum leads to a perivascular hematoma, which can transform into a pseudoaneurysm draining into an adjacent vein [1,6]. Additionally, endothelial cell proliferation promotes the formation of multiple channels between the artery and neighboring veins [1]. According to the second hypothesis (“the laceration theory”), simultaneous injury to an adjacent artery and vein directly forms an AVF [6,10,18].

In our patient, the first hypothesis seems more plausible, as an open scalp wound was noted during her initial admission to the ED and a non-contrast CT scan revealed bilateral scalp hematomas in the parietal regions. Additionally, the fistula was primarily supplied by the left OA and, to a lesser extent, the parietal branch of the left STA, consistent with common vascular patterns in traumatic scalp AVFs [5,19].

Traumatic scalp AVFs typically appear within weeks to several years after the injury, most commonly within the first 3 years after trauma [2,13]. In our patient, a pulsatile mass was noted 3 months after the treatment of an open occipital scalp wound. The temporal and anatomical link between the scalp trauma and AVF formation, in a patient without prior vascular lesions, supports a causal relationship.

Scalp AVFs are classified into 3 types based on the number of feeding arteries and the number of fistulas supplied by these arteries (Table 1) [20]. Our patient’s AVF corresponds to type B.

In summary, traumatic AVFs of the scalp are characterized by 4 key features: (1) formation of a pulsatile mass on the head; (2) enlargement of blood vessels visible on physical examination and angiography; (3) presence of pulsatile sounds on auscultation, which gradually diminish and disappear completely when the main feeding artery is compressed; and (4) presence of draining veins visible on angiography [21].

A comprehensive search of PubMed, Scopus, and Web of Science databases (irrespective of publication language) confirmed the rarity of this complication. Apart from anemia secondary to bleeding from a surgically created AVF in the forearm for hemodialysis [22], only 1 case of traumatic scalp AVF presenting with anemia has been reported [23]. However, Abaunza-Camacho reported a case of sudden blood loss due to AVF rupture, whereas our patient experienced gradual blood loss over several months [23]. The presented case therefore expands the reported clinical spectrum of scalp AVFs, demonstrating that even without rupture, persistent minor bleeding can result in clinically significant hematologic consequences.

Diagnosis of AVFs relies primarily on imaging techniques. Angiography is essential to characterize vascular lesions and to identify the number and origin of feeding vessels (extracranial vs intracranial). DS angiography is considered the gold standard, allowing precise delineation of the lesion and differentiation from slower-flow pathologies (eg, lymphatic or venolymphatic malformations). Other imaging modalities, including CT angiography, magnetic resonance (MR) angiography [2,20], and Doppler ultrasonography [20], are also useful for lesion localization and vascular mapping. Definitive diagnosis is established when CT, MR, or DS angiography demonstrates early venous filling adjacent to the lesion during the arterial phase.

In the presented case, CT angiography of the cerebral arteries was the most helpful diagnostic method in the ED setting. Although DS angiography is considered the gold standard, CT angiography enabled rapid diagnosis of the AVF, allowed assessment of the lesion’s size and vascularization, and excluded any connection to intracerebral vessels.

Due its rarity, there is no universally accepted treatment protocol for scalp AVF [6]. The most common approach is radical surgical excision. Complete removal of the fistula along with the entire lesion is necessary to reduce the significant risk of recurrence [24]. Endovascular embolization, sometimes combined with surgical excision for larger, more complex lesions, is an alternative [25]. Embolization can also be performed with liquid agents, absolute alcohol, or coils [26]. The primary advantage of this approach is reduced intraoperative blood loss. However, the risk of recurrence remains high, particularly in complex lesions [21].

Treatment of traumatic scalp AVFs aims to relieve symptoms and prevent serious complications, such as hemorrhage or diversion of blood flow from the internal carotid system (if intracranial communication exists) [20]. Incomplete treatment can lead to scalp necrosis and hemorrhage [24].

Postoperative scalp defects can be managed with direct closure of small malformations, skin flaps, galeal-pericranial flaps, or free-tissue grafts [27,28]. The latter is particularly useful for covering large defects, although it requires the presence of intact vessels for anastomoses, and the transplanted skin does not support hair growth [29].

In the presented case, embolization of the OA and STA alone controlled the fistula flow and resolved local symptoms. Planned surgical excision and autologous skin grafting were declined by the patient, making embolization the sole definitive intervention, with recurrence risk remaining uncertain.

This case highlights several key points for clinical practice. Persistent pulsatile scalp masses after trauma should prompt evaluation for AVF. CT angiography can suffice for rapid diagnosis in ED settings. Chronic anemia can develop secondary to prolonged minor bleeding, even without fistula rupture. Embolization, surgical excision, or both are essential to prevent recurrence and bleeding, with careful follow-up if treatment is incomplete.

Conclusions

Acquired traumatic AVFs of the scalp are usually a cosmetic concern, but the presented case illustrates that they can rarely cause clinically significant chronic anemia due to persistent bleeding from fragile vessels. Therefore, AVFs should be included in the differential diagnosis of unexplained chronic blood loss.

For emergency physicians, systematic assessment using the SAMPLE and ABCDE approach, including thorough skin inspection, are crucial. When a vascular lesion is suspected, prompt imaging (preferably CT angiography in the ED setting) can rapidly identify the lesion, assess vascular supply, and guide management.

For surgeons, the presented case underscores the importance of timely recognition and appropriate intervention to prevent local and systemic complications, including chronic bleeding from a fistula recurrence. Definitive management can include endovascular embolization, surgical excision, or a combination of both. Reconstructive techniques can be used to repair any resultant scalp defects. In the presented case, embolization alone controlled fistula flow and resolved the patient’s symptoms. However, the long-term recurrence risk remains uncertain, highlighting the need for careful follow-up.

Finally, this case highlights the need for larger studies (or a multi-center registry) to evaluate traumatic scalp AVF complication rates, compare outcomes of different treatment, and to refine the diagnostic and therapeutic approach in the ED.