**3. Aetiology**

*Aortic Aneurysm and Aortic Dissection*

million [31.1–43.9 million] people living with HIV, of whom 35.1 million [29.6–41.7 million] adults. The majority of these individuals reside in the developing world [1]. HIV infection involves multiple systems including the cardiovascular system. A structure of the HIV virus and its replication in a cell are depicted in **Figures 1** and **2**. A large number of these patients present with vascular pathology [3, 4]. HIV afflicts the vascular system in multiple ways. Patients may present with a diverse array of aneurysms, occlusive disease, spontaneous arteriovenous fistulae and dissections. The precise pathogenesis of HIV related vasculitis remains poorly understood, a few

*Diagram illustrating HIV replication. (A) The virus glycoprotein receptors bind to host cell CD4 and a co-receptor CCR5. (B) Fusion of the virus with the host cell membrane results in viral uncoating and the release of the viral nucleocapsid into the cytoplasm. (C) The enzyme reverse transcriptase converts the single stranded RNA into double stranded DNA. (D) The viral DNA is transported to the host nucleus where it is integrated into the host's DNA. (E) Viral DNA is transcribed and translated using host cell machinery and then cleaved by viral protease into functional viral proteins. (F) Viral RNA and proteins assemble at the cell surface and bud off the cellular membrane. (Reproduced from Ref. [2]. Permission obtained from Michael S Pepper).*

In this chapter we will review the current knowledge pertaining to the important entity of HIV associated vasculopathy with an emphasis on effects of HIV on the aorta.

An aortic aneurysm is a dilation of a segment of the aortic wall, which may undergo further expansion and rupture [6]. It is defined as at least a 50% increase in diameter compared with the expected normal diameter of the vessel. They may

It may be fusiform or saccular in morphology [6]. A fusiform aneurysm is characterised by a uniform symmetric enlargement of the entire circumference of the aortic wall. A saccular aneurysm involves dilation of a localised portion of the aortic wall.

recent studies have tried to address this issue [5].

**2. Definition and broad overview of aortic aneurysms**

occur in the ascending or the descending thoracic or abdominal aorta.

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**Figure 2.**

There are multiple aetiologies implicated in the pathogenesis of aortic aneurysms [6]. These include:

