Page 150 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

126 J. Charles Jennette, Ronald J. Falk and Adil. H. M. Gasim

neutrophils and conspicuous fibrinoid necrosis. LVV may have focal areas of medial
coagulative necrosis, possible caused by occlusion of vasa vasorum. It is important to realize
that within a week or two of the inception of a focus of acute inflammation in MVV and
SVV, the inflammation at that site evolves into chronic inflammation with replacement of
neutrophils and necrosis by mononuclear leukocytes and scarring that can be
indistinguishable pathologically from chronic LVV. However, many forms of MVV and
especially SVV have multiple sites of inflammation arising at different times so that there
may be at least some diagnostic acute lesion in a tissue specimen even if there are many less
specific chronic lesions.

The two major categories of LVV are TAK and GCA. Although on average there are
some pathological and clinical features that differ between these two categories of disease, the
most objective difference is that the onset of TAK is primarily before 50 years old while that
of GCA is typically after age 50 years. Thus, CHCC 2012 defines Takayasu arteritis (TAK)
as arteritis, often granulomatous, predominantly affecting the aorta and/or its major branches
with an onset usually in patients younger than 50 [1]. GCA is defined as arteritis, often
granulomatous, usually affecting the aorta and/or its major branches, with a predilection for
the branches of the carotid and vertebral arteries, often involves the temporal artery, and with
onset usually in patients older than 50 and often associated with polymyalgia rheumatica
(PMR) [1].

In the past, the term temporal arteritis was used as synonymous with GCA but this is not
an acceptable approach because not all GCA involves the temporal arteritis and not all
vasculitis affecting the temporal arteries is GCA. For example, the temporal arteries can be
affected by polyarteritis nodosa (PAN), MPA, and [6-8].

Active aortitis and arteritis of TAK and GCA is characterized by transmural
inflammation with influx of monocytes, macrophages and lymphocytes (predominantly T
lymphocytes) [3-5]. Multinucleated giant cells, formed by the fusion of monocytes into
syncytial cells, often are identifiable but are not required for a pathologic diagnosis (Figure
2). Weakening and dilation of vessel walls results in aneurysm formation, and scarring and
fibrotic intimal thickening result in narrowing of lumens and ischemia in downstream tissues.
In arteries with an elastic media, such as the aorta and its initial branches, special stains for
elastic demonstrate a mouth eaten appearance with irregular zones of lysis of the multi-
laminated elastic media. In non-elastic arteries, there is focal fragmentation of the internal
elastics at the junction between the media and the intima. Fibrinoid necrosis is uncommon
and when present is usually a minor feature of the overall injury. The presence of extensive
fibrinoid necrosis should raise the possibility of some form of MVV or SVV [6-8].

Medium Vessel Vasculitis (MVV)

CHCC 2012 [1] defines MVV as vasculitis predominantly affecting medium arteries
defined as the main visceral arteries and their branches. Any size artery may be affected and
inflammatory aneurysms and stenoses are common. In the acute phase, the inflammation
typically is accompanied necrosis, which may result of spillage of plasma constituents into
the vessel wall and perivascular tissues where the constituent coagulation cascade contacts
thrombogenic stimuli, including tissue factor, resulting in the formation of fibrin. This

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