Colin Berry

Fundamental lesions in vascular pathology

Thrombosis is defined as the formation of a solid mass in the circulatory system from the elements of the blood during life.

Histology of vessels

The cardiovascular system consists of four main types of vessel: arteries, veins, capillaries and the less well defined sinusoids. No vessel (small or large) should be seen as a simple conduit; all have distinct functional characteristics, which, in turn, will affect organ function profoundly, and their structure is modified by the functional demands they must satisfy. As an arbitrary definition we can say that any vessel whose diameter is larger than 250 to 300 lam and visible to the naked eye belongs to the macrocirculation and that the microcirculation is made up of vessels measuring less than 250 μm in diameter [1].

Non-atherosclerotic and non-vasculitic diseases

First reported by Leadbetter and Burkland in 1938 [1], fibromuscular dysplasia (FMD) is a segmental, non-atheromatous and non-inflammatory disease affecting mostly intermediate size arteries. It is manifest by consistent alterations in the smooth muscle cells of arteries, associated with modifications of the extracellular ground substance. Recent progress in diagnostic imaging allows more precise diagnosis of the location and type of lesions and, in general, pathologists have few opportunities to study fibromuscular dysplasia. X-ray-controlled angioplasty or embolization [2–4] now deals with most of the lesions and operative surgery is carried out only when angioplasty fails. The morphological pattern of fibromuscular dysplasia now seen by the pathologist is a mixture of the primary lesions plus the changes produced by the complications of angioplasty. Many so-called natural complications (dissecting haematoma, aneurysm, AV fistula) result directly from the invasive techniques.

Developmental anomalies and hereditary diseases of vessels

Congenital vascular anomalies can be divided into three groups: those developing during intra-uterine life, those associated with karyotype aberrations, and those arising from the effects of single genes or complex polygenic mutations. There are no good data on the incidence of these lesions; a recent Finnish study on 4346 new-borns showed a 3.8% rate of vascular lesions excluding salmon patches on the head and neck, in general agreement with other studies [1]. Seventy to 80% of lesions are said to regress spontaneously by the age of seven years. In most instances of this type of lesion both blood and lymphatic vessels may be affected.

Effects of physical and chemical agents on vessels

When vessels are exposed to ionising radiation experimentally there is immediate damage to the endothelium, with increased permeability and necrosis followed by healing with intimal proliferation and vascular stenoses. Smooth muscle cells undergo more subtle damage resulting in loss of cellularity of the media and replacement by fibrosis. Radiation also induces a chronic antiangiogenic effect and contributes to growth abnormality, for example, in limb development [1, 2]. In man, long-term complications of radiation injury are still commonly seen despite advances in radiotherapy. Acute effects are largely time dependent and can be controlled by alteration of therapy schedule. For chronic changes, the age at the time of exposure to radiation does not seem to affect the time of the onset of lesions. No direct correlation has been established between the severity of the injury and the dose of radiation and the true incidence of radiation-induced vascular changes is almost certainly underestimated. The duration of time between exposure and development of post-radiation changes varies from months to 24 years, with a mean of 14 years [3–7], and further complications (tissue necrosis, infection, and ulceration) may occur later. The clinical patterns depend on the role of the organ system involved, and ischaemic syndomes, erectile dysfunction [8], aortic arch syndrome or pulseless disease [9], aneurysms, veno-occlusive liver disease [10] and vascular rupture [11] have all been reported. In children, moyamoya syndrome has been reported following radiation therapy for tumours at the base of the brain [12].

Thrombosis and embolism

Thrombosis is the formation of a solid mass, derived from the consituents of the blood, within the vascular system during life. As an important part of haemosta-sis, it depends on a normally functioning endothelium and underlying subendothelial layer, platelets, and the coagulation cascade.

Tumours of vessel wall components and vascular related structures

Most angioleiomyomas develop from the smooth muscle cells of the media or adventitia, most frequently in a subcutaneous vein, but larger veins (hepatic, femoral) may be involved. The tumour affects patients between the fourth and sixth decades with a predilection for females. The most frequent locations are in the legs and arms [1–3]. Other sites include the skin, nasal mucosa or the pharyngeal space [4–7]. An angioleiomyoma appears as a circumscribed mass, usually measuring about 2 cm in diameter, rarely larger than 4–5 cm. Pain, present in half of the cases, may be exacerbated by menses, pregnancy, pressure and changes in temperature. Simple excision is adequate treatment.

Vascular tumours and tumour-like conditions

In this area the terminology is often confused, and even misleading. In many conditions, especially with regard to the benign lesions, the clinical and familial history are of great importance in diagnosis.

Vascular changes in metabolic and endocrine disorders

In a number of metabolic diseases, involvement of the heart and blood vessels is a central part of the disease process; in some the disease is manifest by virtue of a cardiovascular change or complication [1] It is these conditions which will be considered here.

Vessels and infectious diseases

Blood vessels and lymphatics play a central role in many infections or infestations. Viruses, bacteria fungi and parasites may all disseminate through vessels or demonstrate a tropism for vessel walls or a capacity to parasitise vessels in the long term, with mechanical complications. Vasculitis (see chapter XI), disseminated intravascular coagulation and thrombosis may occur [1, 2]. There is direct and indirect evidence establishing links between infection and vascu-lopathy, including aortitis, atherosclerosis, Wegener’s granulomatosis and various vasculitic syndromes [3]. However, most complications are caused by the infectious disease itself (via toxins, haemolysis or cross-reacting antigens) or are facilitated by changes in the response of the immune system [4, 5].