IgG4-Related Aortitis Masking as Intramural Hematoma on Imaging

Abstract

Background

IgG4-related aortitis is a rare fibroinflammatory disease characterized by thoracic or abdominal aortic wall thickening and dilation.

Case Summary

A 24-year-old man presented after blunt trauma and was found to have intramural hematoma in the ascending aorta on chest computed tomography. Given the high-impact injury, aortic injury could not be excluded. Therefore, he underwent a hemiarch replacement; intraoperative findings and histopathology were concerning for IgG4-related aortitis.

Discussion

IgG4 aortitis of the ascending aorta is rare, with only a few case reports in the literature. On computed tomography, IgG4 aortitis can mimic acute aortic syndrome, which poses a challenge regarding appropriate management.

Take-Home Messages

IgG4 aortitis can mimic acute aortic syndrome findings on imaging. This poses a clinical dilemma in the management of these patients, and surgical intervention should only be offered in the appropriate clinical scenario.

Visual Summary

Visual Summary.

IgG4-Related Aortitis Presenting as Acute Aortic Syndrome on Chest Computed Tomography

The arrow denotes intramural hematoma.

History of Presentation

The patient was a healthy 24-year-old man who presented to the emergency department after a motor vehicle collision. He was riding a motorcycle without a helmet and suffered a high-impact injury, with brief loss of consciousness. He denied any chest pain or shortness of breath. Upon arrival, he was hemodynamically stable, and physical examination was unremarkable besides multiple scattered abrasions. There were no concerns for neurologic or vascular injury on physical examination. A computed tomography (CT) scan of his chest revealed a right clavicular fracture, dilated ascending aorta (4.0 cm) with intramural hematoma extending to the great vessels, and focal outpouching of contrast posteriorly, suggesting a traumatic pseudoaneurysm (Figure 1A).

Take-Home Messages

• •IgG4-related aortitis can mimic acute aortic syndrome findings on imaging.
• •This poses a clinical dilemma in the management of these patients, and surgical intervention should only be offered in the appropriate clinical scenario.

Figure 1.

Preoperative Imaging and Intraoperative Finding

(A) Focal outpouching of contrast (red arrow) posteriorly along ascending aorta into a region of the thickened arterial wall (∗), intramural hematoma (yellow arrow). (B) Excised gross aortic specimen with thickened wall and irregular lumen, and a punctate intimal tear (black arrow) corresponding to the outpouching shown on CT. (C) Thickened ∼1-cm aortic wall (∗). CT = computed tomography.

Past Medical History

The patient had no medical issues.

Differential Diagnosis

Considerations included aortic transection, pseudoaneurysm, acute aortic syndrome/intramural hematoma, infectious aortitis, noninfectious aortitis, and immunoglobulin G4 (IgG4) aortitis.

Investigations

The patient was admitted to the cardiovascular surgical intensive care unit for close hemodynamic monitoring. Follow-up chest computed tomography angiography obtained after 24 hours showed a possible increase in the size of the outpouching aortic wall.

Management

Given the high-impact injury and imaging findings, the patient was taken to the operating room for a hemiarch ascending aortic replacement. Intraoperative transesophageal echocardiography revealed soft tissue inflammation of the ascending aorta that corresponded with the CT findings. We approached this via a median sternotomy. During pericardiotomy, significant intrapericardial adhesions were noted from the mid ascending aorta to the innominate vein, along the pulmonary artery and left ventricle. After meticulously lysing these adhesions, the ascending aorta was exposed. We initiated cardiopulmonary bypass through an arterial cannula in the ascending aorta and dual-stage venous cannula in the right atrium. A left ventricular vent was placed through the right superior pulmonary vein, and a retrograde superior vena cava catheter was placed for retrograde cerebral perfusion. The patient was then cooled to 25 °C.

The aorta was thick and significantly adherent to the pulmonary artery, precluding any safe dissection in this area. An aortotomy was then made in the mid ascending aorta to visualize the ascending aorta and arch. This revealed a 1-cm thickened aortic wall, without any dissection flap or false lumen. However, a 1- to 2-mm punctate intimal tear was identified in the posterior distal ascending aorta (Figures 1B and 1C). Although there was no frank extravasation of blood through the punctate defect, the adjacent necrotic and inflamed soft tissue was containing this defect. The ascending aorta was then transected distally toward the base of the arch vessels and proximally at the level of the sinotubular junction. The diseased aorta (Figure 1) was sent to pathology, and a hemiarch replacement was conducted using a 32-mm synthetic vascular graft (Hemashield). The patient was weaned off cardiopulmonary bypass, and the rest of the operative course was uneventful.

Outcome and Follow-Up

The patient had an uneventful postoperative course and was discharged home on postoperative day 5. Final pathology revealed subintimal neutrophilic abscesses in the ascending aorta, transmural chronic inflammation, granuloma formation, lymphoplasmacytic infiltrate, and focal multinucleated giant cells, consistent with immune-mediated disease process (Figure 2). Elastin staining showed multifocal disruption of the elastic lamina by inflammatory infiltrate. Immunostaining for CD138 and IgG4 revealed an increased number and proportion of IgG4-positive plasma cells; there were 60 to 80 IgG4+ plasma cells per high-power field and >50% IgG4 (+)/IgG ratio expressed by plasma cells, suggesting IgG4-related disease. The tissue was negative for acid-fast bacilli and fungal organisms. Based on the histopathologic findings, the patient was diagnosed with IgG4-related aortitis. Serum IgG subclasses were tested and were within normal limits. He then underwent a positron emission tomography (PET)/CT to evaluate for residual areas of IgG4-related disease, which was negative.

Figure 2.

Immunohistochemical, and Hematoxylin and Eosin Stains of the Aortic Specimen

Immunohistochemical staining of lymphoplasmacytic infiltrate for (A) IgG4 and (B) CD138, a pan-IgG marker. (C) Hematoxylin and eosin stains of the aortic wall showing multinucleated giant cells and (D) granuloma formation.

The patient has been following up with rheumatology, with plans for disease surveillance with PET/CT and chest magnetic resonance angiography. He has not had recurrence of aortitis for 3 years after surgery.

Discussion

IgG4-related aortitis involves inflammation and fibrosis of the aortic wall, specifically the media and adventitia layers. It can be isolated, with disease confined to the aorta, or as part of systemic large vessel vasculitis.^1,2 It is thought to represent 0.6% to 4% of all surgical thoracic aortic lesions, although the true incidence is unknown.^3,4 It rarely involves the ascending aorta, with a few case reports in literature.⁵ Although the pathophysiology of isolated IgG4-related aortitis remains unclear, studies have suggested that it is a sequela of an inflammatory pathway that activates helper T cells, thereby triggering cytokine release and plasma cell infiltration.^6,7 This leads to destruction of aortic wall, fibrosis, and remodeling of periaortic tissue. Gradually, this results in severe medial elastic fiber defects and obliterative phlebitis of the vasa vasorum. This eventually leads to weakening of the aortic wall and predisposes it to aneurysm formation.^5,6 Various mechanisms have been proposed to explain the anatomical distribution of IgG4-related aortitis, but none are conclusive. The primary hypothesis focuses on the association of chronic IgG4-related aortitis with retroperitoneal fibrosis. The contiguity of the adventitia of the abdominal aorta with the retroperitoneal connective tissue may allow immune cell recruitment and propagation of the disease.⁸

Diagnosing IgG4-related aortitis is challenging, as aortic tissue specimen is not always available. Therefore, various diagnostic criteria have been developed to establish a diagnosis using a combination of laboratory results and radiologic and pathologic findings.^5,9 Our patient met 2 such criteria, namely, radiologic and pathologic findings. An important aspect of diagnosing IgG4-related aortitis is excluding an infectious etiology. In our patient, serum tests for infections as well as tissue culture from the aortic wall were negative. Once the diagnosis is established or if there is a high suspicion for IgG4-related aortitis, patients can be treated with steroids, immunosuppression, or targeted monoclonal antibody. However, they may eventually require surgical intervention for aortic aneurysm, or in our case when image is concerning for acute aortic syndrome in the appropriate clinical context. Regardless, patients should be surveilled with cross-sectional imaging to monitor aneurysmal deformation of the aortic wall, especially if they are being treated with steroids. PET/CT is a valuable imaging modality to evaluate for disease progression and to monitor treatment response. Factors such as male sex, serum IgG4 elevation, older age, and organ involvement increase the pretest probability of IgG4-related aortitis. Therefore, a multimodal approach to diagnosis can be useful.

IgG4-related aortitis can mimic acute aortic syndrome on CT scans. In our case, we had an appropriately high suspicion for aortic injury in the setting of high-impact trauma. Therefore, we decided to surgically intervene for this image finding. However, in certain clinical scenarios, such as a young, asymptomatic patient with no risk factors for aortic injury, surgical intervention may not be appropriate for this incidental finding. This poses a clinical dilemma, as the treatment for aortitis is starkly different from that of acute aortic syndrome, and the risks of missing an aortic injury can be lethal. Therefore, it is imperative to discuss IgG4-related aortitis, which can mask as a life-threatening injury on imaging. Additional imaging can elucidate whether this is a chronic versus acute finding and guide the next steps. Serum IgG4 levels can be used as adjunct data, when time permits, to determine whether there is a component of immune-related aortitis.

Conclusions

IgG4-related aortitis can mimic acute aortic syndrome on imaging. The treatment for these 2 disease processes is starkly different. Therefore, in the appropriate clinical setting, the possibility of aortitis should be considered and followed up with further testing and appropriate management. A majority of aortitis cases involve the abdominal aorta, unlike our case in which the ascending aorta was involved. Additionally, isolated ascending aorta involvement is rare, as other major blood vessels and organs are commonly involved. The clinical presentation of this patient's underlying disease—traumatic aortic injury in the context of aortic tissue that was already inflamed or weakened—was also unusual. Our case adds to the current literature on this condition, highlighting a rare presentation and providing insight into the challenging diagnosis and treatment of IgG4-related aortitis.

Funding Support and Author Disclosures

The authors have reported that they have no relationships relevant to the contents of this paper to disclose.