Case 3c -

Arteriovenous Malformation Harry Kozakewich Children's Hospital Boston Boston, MA

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Clinical History: This 7 year old boy was born with a capillary stain on his scalp at the frontal hairline margin. Over the ensuing years, a dome-shaped mass gradually appeared. Upon examination, dilated vessels were seen at the periphery and pulsation was appreciated upon palpation. The lesion was embolized 24 hours prior to excision (1997). Four years later, there was no evidence of recurrence. Case 3c - Figure 1 Case 3c - Figure 2 Case 3c - Figure 3 Case 3c - Figure 4 Case 3c - Figure 5 Case 3c - Figure 6 Case 3c - Figure 7 Case 3c - Figure 8 Case 3c - Figure 9 Differential Diagnosis: 1. Arteriovenous malformation 2. Venous malformation 3. Vasoproliferative lesion Pathologic Findings: The submitted images show massive and tortuous arteries and large hypermuscularized veins in the dermis and subcutis. Some arteries have lost their internal elastic lamina, have thinned and aneurysmal walls, and transition to other thick-walled vessels with intimal proliferation, possibly veins. There is a sprinkling as well as irregular clusters of small vessels with round lumens and one or more layers of muscle. The histopathology is consistent with arteriovenous malformation (AVM), which in this patient has a rather prominent small vessel component. Final Diagnosis: Arteriovenous Malformation Discussion: AVMs are seen at birth in approximately half of affected patients with the rest usually becoming apparent during childhood. [1, 2] They are most common in the head and neck region, particularly the brain, but also occur in skin, soft tissue and viscera. Most are quiescent until adolescence and progress thereafter. [3, 4] The majority are sporadic but some are components of CM-AVM, [5] Parkes Weber, [2] andPTEN hamartoma tumor syndromes [6, 7] and hereditary hemorrhagic telangiectasia, [8] The pathogenesis of AVMs is not well understood, but the end result is loss or modification of the capillary bed and shunting between small arteries. The histopathology of AVMs of soft tissue varies widely from one area to another in a particular specimen. Generally, there are large and tortuous arteries, large thick-walled hypertensive veins, large thin-walled channels (presumably veins) and some number of indeterminate smaller vessels. Some arteries show disruption and fragmentation of the arterial internal elastic lamina and transition to vessels with the appearance of hypertensive veins, representing sites of shunting. Identification of arteriovenous shunts is aided by an elastic stain, but they may be small and difficult to demonstrate. In the early stage, the veins show a reactive hypertrophy of the smooth muscle layer, and later, the smooth muscle is replaced by collagen, resulting in thin, fibrotic, inelastic vessels. [9, 10] Intimal and adventitial fibrosis are common. A small vessel component of a variable degree is present in most AVMs. Several patterns may be seen although there is overlap. One pattern has dispersed round small vessels, approximately 20-50 microns in diameter with fibrous walls containing one or two layers of pericytes/smooth muscle cells, and few if any elastic fibers. The second features aggregates or lobules of small, plump curved vessels of capillary type having elongated endothelial cells with abundant eosinophilic cytoplasm, scattered pericytes and an intervascular collagenous and mucinous matrix. Another pattern has closely packed capillaries with round lumens and plump endothelium and pericytes. This microvascular component, when detected in cutaneous ulcers or papules, is often referred to as pseudo-kaposiform. [11] A detectable proliferative index is present in most AVMs. [12] but the reason for the proliferation is uncertain. It may result from modification of the microvasculature in order to accommodate the increased blood flow or may be intrinsic to the genesis of AVM. The diagnosis of AVM is usually made clinically and biopsies for diagnosis are uncommon. A histopathologic diagnosis is usually difficult, particularly in a small biopsy and should be suggested or made only after correlation with clinical and imaging features. Certain lesions in particular can mimic AVMs. One such type occurs intramuscularly in children and adolescents may extend into subcutis and skin. A lobular component is prominent and composed of small, round or curved channels with plump endothelium and pericytes with channels and lobules separated by fibrous tissue. There is some similarity of the lobules to pyogenic granuloma. Numerous extralobular arteries and veins are present, particularly the latter, some of which have mural myofibroblastic and smooth muscular proliferation. A large series was reported with most incorporated under the designation "intramuscular hemangioma of the small vessel type". [13] Others have also raised the possibility that these might be tumors rather AVMs. [14] However, others are of the opinion that these lesions are a form of AVM. [15] Another entity that is often misdiagnosed as AVM is PTEN hamartoma of soft tissue. These lesions occur primarily in children and young adults and are intramuscular but may extend to skin and soft tissue. They feature overgrowth of fibromyxoid and adipose tissue, tortuous arteries and veins with transmural smooth muscle hyperplasia, labyrinthine veins, arteriovenous shunts, lymphoid germinal centers and sometimes bone formation and intraneural Schwann cell hyperplasia. [6, 7] References: North PE, Mihm MC. Histopathological diagnosis of infantile hemangiomas and vascular malformations. Facial Plastic Surg Clin North Am 9:505,2001. Garzon MC, Huang JT, Enjolras I. et al. Vascular malformations. Part 1. J Am Acad Dermatol. 56:353,2007. Enjolras O, Logeart I, Gelbert F et al. Malformations artérioveineuses:étude de 200 cas. Ann Dermatol Venereol 127:17,1999. Kohout MP, Hansen M, Pribaz JJ et al. Arteriovenous malformations of the head and neck: natural history and management. Plast Reconstr Surg 102:643,1998. Eerola I, Boon LM, Mulliken JB, et al. Capillary malformation-arteriovenous malformation, a new clinical and genetic disorder caused by RASA1 mutations. Am J Hum Genet 73:1240,2003. Howard EL, Tennant LB, Upton J, et al. PTEN- associated vascular anomaly. Mod Pathol 18:309,2005. Tan WH, Baris HN, Burrows PE et al. The spectrum of vascular anomalies in patients with PTEN mutations: implications for diagnosis and management. J Med Genet 44:594,2007. Khalid SK, Garcia-Tsao G. Hepatic vacular malformations in hereditary hemorrhagic telangiectasia. Semin Liver Dis 28:247,2008. Leu HJ. Zur Morphologie der arteriovenosen Anastomosen bei kongenitalen Angiodysplasien. Morphol Med 2:99,1982. Mulliken JB, Dethlefson SM. A preliminary morphologic study of an arteriovenous malformation and adjacent vasculature. In St.Belov, Loose DA, Weber J (Eds) Periodica Angiologica. Hamburg: Einhorn-Presse Verlag 16:50, 1989. Bluefarb SM, Adams LA. Arteriovenous malformation with angiodermatitis: Stasis dermatitis simulating Kaposis's disease. Arch Dermatol 96:176,1967. Meijer-Jorna LB, van der Loos CM, de Boer OJ, et al. Microvascular proliferation in congenital vascular malformations of skin and soft tissue. J Clin Pathol 60:798,2007. Allen PW, Enzinger FM. Hemangiomas of skeletal muscle: An analysis of 89 cases. Cancer 29:8,1972. Hein KD, Mulliken JB, Kozakewich HP, et al. Venous malformations of skeletal muscle. Plastic Reconst Surg 110:1625,2002. North P, Kozakewich H. In Vascular Malformations and Tumors in Children. Society for Pediatric Pathology Seminar, San Antonio, Tx. Feb.26, 2005.