Spontaneous pseudoaneurysm of the superficial temporal artery in neurofibromatosis type 1: illustrative case

Abstract

BACKGROUND

A pseudoaneurysm of the superficial temporal artery is an uncommon clinical entity that has largely been linked with direct traumatic causes. Neurofibromatosis type 1 (NF1)-related vasculopathy is a rare cause of idiopathic arterial bleeding in the craniofacial region.

OBSERVATIONS

A 46-year-old male with clinical features of NF1 presented to the hospital with an enlarging and tender right temporal mass without a history of trauma. Computed tomography angiography suggested the development of a pseudoaneurysm, and surgery was performed to resect the mass. Histopathological examinations showed focal interruption of the epithelium layer and elastic lamina, well-demarcated thickening of the smooth muscle layers of the arterial wall, supporting the diagnosis of pseudoaneurysm.

LESSONS

NF1-associated vasculopathy is likely the predisposing factor for the development of a superficial temporal artery pseudoaneurysm.

A pseudoaneurysm of the superficial temporal artery (STA) is an uncommon clinical entity, and patients usually present with increasing swelling at the temporal area. Since its first description in a young patient in 1740, there have been only a limited number of case reports in the literature.^1–5 The frontal branch has appeared to be more vulnerable than the parietal branch, and this corresponds with a suggested traumatic etiology. Clinical features include a pulsatile mass associated with headache. Given the risk associated with arterial bleeding, it usually requires urgent surgical management. Neurofibromatosis type 1 (NF1), also known as von Recklinghausen’s disease, is an autosomal dominant neurocutaneous condition caused by mutations in the tumor suppressor gene NF1. NF1 has been suggested to cause vasculopathy,⁶ such as stenosis, occlusion, aneurysm,⁷ pseudoaneurysm,⁸ and arteriovenous fistula.⁹ To our knowledge, this is the second case report on the development of an STA pseudoaneurysm in a patient with NF1.

Illustrative Case

A 46-year-old male presented to a local emergency department for a progressively enlarging and painful mass in his right temporal area. He denied any head trauma history except for a vague memory of slapping a mosquito bite with his hands 4 days earlier. On presentation, he was fully conscious with a Glasgow Coma Scale score of 15 and no neurological deficits. A pulsatile tender mass with a diameter of approximately 8 cm was appreciated in the right temporal-auricular area suspicious for hematoma (Fig. 1A and B). Additionally, there was café-au-lait spotty pigmentation and multiple subcutaneous masses of different sizes on his trunk and limbs (Fig. 1C and D); both were typical in patients with NF1.

FIG. 1.

A progressive, enlarging, tender right temporal mass about the size of a ping pong ball developed without a trauma history. The mass (red arrowheads) was better appreciated when looking from above and extended into posterior auricular area (A and B). Although there had been no previous diagnosis, the patient showed clinical features of NF1 including café-au-lait macules and neurofibromas on the trunk (C and D) and limbs. Cranial CTA (E) suggesting an STA pseudoaneurysm, mainly involving the parietal branch (red arrowheads) with the proximal artery exhibiting fusiform dilation (F).

A cranial computed tomography angiography (CTA) scan was obtained and demonstrated a mass that was approximately 4 × 3 × 3 cm, suggestive of a pseudoaneurysm. There was no evidence of intracranial hematoma or vascular abnormality (Fig. 1E and F). The patient was transferred to our tertiary neurosurgical center for emergent surgery under general anesthesia, and intraoperative findings confirmed that a pseudoaneurysm had developed where the STA bifurcates into the parietal branches, with the proximal artery exhibiting fusiform dilation. Through the superficial temporal fascia, the proximal STA was isolated, and the proximal edge of the artery was clamped. The aneurysm was exposed and opened to remove all of the thrombus. The proximal arterial segment also appeared abnormal and was resected and sent for pathology.

The postoperative course was uneventful. On the first postoperative day, a second cranial CTA was performed to confirm the complete removal of the pseudoaneurysm. CTA of the thoracoabdominal aorta was also performed and ruled out other vessel diseases. The patient was discharged on the second postoperative day.

Histopathological examinations showed focal interruption of the epithelial layer and elastic lamina, well-demarcated thickening of the smooth muscle layers of the arterial wall. Arterial wall structural damages were more prominent in the distal than in the proximal segment. Immunohistochemical staining showed positivity of markers of endothelial cells (CD31) and smooth muscle cells (smooth muscle actin, desmin, and vimentin) but negative for MyoD1, CK, and NF, supporting the diagnosis of pseudoaneurysm (Fig. 2). There was no sign of recurrence at the 6-month clinical follow up.

FIG. 2.

Pathological examination confirmed the diagnosis of pseudoaneurysm. Hematoxylin and eosin staining showed gross thickening of endothelial and smooth muscle layers in the proximal artery but disruption of vascular integrity more distally (A–C: proximal to distal). Elastic tissue (D) and CD31 (E) staining showed a disrupted epithelial layer and internal elastic lamina (arrowheads) and strong expression of smooth muscle actin (E) in the expanded vessel wall (proximal artery: A–F). Elastic tissue (G) and CD31 (H) staining showed more severe disruption of epithelial and elastic layers, and desmin staining (I) confirmed expansion of the smooth muscle layer (distal artery: G–I). Original magnification × 40 (A–I).

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

A pseudoaneurysm of the STA is an uncommon entity in the literature, and most have been reported to develop from traumatic events, such as blunt or penetrating trauma, or from iatrogenic causes, such as temporomandibular arthroplasty, hair transplantation, injections, or facelift. The superficial location of the STA makes it susceptible to the above traumatic insults that result in incomplete breach of the arterial wall with progression to a pseudoaneurysm subacutely. Very rarely, the patient cannot recall any predisposing traumatic event.¹⁰ The differential diagnosis of a temporal artery pseudoaneurysm includes true aneurysm,¹¹ sebaceous cyst, lipoma, lymphadenopathy, arteriovenous fistula, hematoma, or abscess.

The unique knowledge we learned from the current case is that the incidental diagnosis of NF1 is likely to be a predisposing condition. NF1 clinical features include café-au-lait macules on the skin, neurofibromas of the peripheral nerve, and optic pathway gliomas. Vascular abnormalities, first described in 1945, are rare but known manifestations of NF1 and comprise stenoses,¹² aneurysms,¹³ pseudoaneurysms,¹⁴ fistula formation, occlusions, and arteriovenous malformations. However, reported NF1 vasculopathy has mainly involved large vessels like renal artery stenosis, abdominal aortic coarctation, internal carotid artery aneurysms, and cervical vertebral arteriovenous malformations. To the best of our knowledge, this is the second report of a pseudoaneurysm of the STA, branches of the external carotid artery, in a patient with NF1. The other patient in the literature had a similar story of previously undiagnosed NF1 with the sudden onset of right temporal swelling in the abscence of trauma, which was found to be an STA pseudoaneurysm on angiography.¹⁵ Interestingly, in that patient, both the parietal and frontal branches were found to be bleeding and were consecutively embolized. Despite this small case number, we hypothesize that a spontaneous pseudoaneurysm can be a manifestation of NF1 vascular abnormality. This is supported by the fact that the parietal branch was affected in both cases, which is in contrast to more trauma-prone frontal branches in the literature. Intraoperatively, the segment of the artery proximal to the pseudoaneurysm was macroscopically abnormal, and pathological examination confirmed partial disruption of the vessel wall. Therefore, the underlying NF1 vasculopathy can develop silently until acute transection of the arterial wall, leading to extravasation and the formation of distal pseudoaneurysm bulk. This may also explain why NF1 patients have a more acute clinical course than reported traumatic cases (usually 2 to 6 weeks if traumatic events were identified).¹⁰ Also, most cases of pseudoaneurysm of the STA were reported to be nontender, probably because of their small sizes (approximately 1 cm). In contrast, our patient came to medical attention mainly because of severe headache, which was likely due to mass effect from the large pseudoaneurysm bulk.

Vascular vulnerability/fragility are likely to be the cause of pseudoaneurysm. Histopathological findings in NF1 vasculopathy includes media cystic degeneration, disruption of the tunica elastica, and fibromuscular dysplasia (proliferation of spindle cells in the arterial wall), all of which lead to weakening of the endoplasmic plate.¹⁶ In the presence of scalp neurofibromas, direct compression of the vasculature or luminal infiltration by the tumor mass may be a contributing factor. We are still unclear about the molecular basis of NF1 leading to vascular structural and/or functional abnormality, although the deficiency of tumor suppressor neurofibromin (coded by NF1) seems to impact the integrity and/or repair of vascular wall structures. Neurofibromin has been identified in the endothelial and smooth muscle cells of blood vessels. Neurofibromin can activate cell proliferation via downregulating the Ras-Raf/mitogen-activated protein kinase signaling pathway, and the loss of neurofibromin produces increased mitogenic signaling and leads to increased cellular proliferation or differentiation. It has been proposed that loss of the maintenance effect of neurofibromin will lead to rigid/fragile blood vessel structures because of fibromuscular hyperplasia, which is the main reason for intimal thickening.^17–19 Acute exacerbation of symptoms in our case suggested an impaired intrinsic hemostasis mechanism such as arterial constriction in NF1 vasculopathy.

Lessons

Because NF1 vascular abnormalities usually involve multiple arterial vessels that are potentially subject to sudden rupture with devastating consequences, screening of vasculopathy in large vessels using a noninvasive diagnostic tool (CTA, magnetic resonance angiography) may be warranted in patients with NF1 and superficial manifestation of arterial disease as in our case. Screening of other family members for vasculature-related issues may be considered especially when there are concurrent neurocutaneous features of NF1. Although there is no consensus on the optimal frequency of vascular imaging, selective noninvasive imaging if there is clinical suspicion is justifiable in our opinion.

Resection of the diseased vasculature with evacuation of hematoma is the preferred strategy for superficially located pseudoaneurysms, and the technique is similar to temporal artery biopsies. Arterial reconstruction is controversial given the rich collateral supply of the scalp. One theoretical benefit would be preservation of the donor artery if STA-MCA bypass surgery is required later for the treatment of occlusive cerebrovascular disease.²⁰ Surgical complication is minimal with the potential risk of injury to the temporal branch of the facial nerve. Other treatment options include endovascular embolization, which is less desirable in terms of decompression of the mass effect from the hematoma.

Acknowledgments

This work was supported by Science Technology Department of Zhejiang Province (No. IGF22H160060) and Health Science and Technology Plan of Zhejiang Province (No. 2021KY794 and 2023KY147).

Author Contributions

Conception and design: Sheng, Shen, Li. Acquisition of data: Li, Shan. Analysis and interpretation of data: Li, Ji. Drafting the article: Shen, Li. Approved the final version of the manuscript on behalf of all authors: Sheng. Study supervision: Sheng, Shen.

Supplemental Information

Previous Presentations

Conference poster presentation at RCPA Pathology Update 2023 in Melbourne, Australia, February 24–26, 2023.