Arteriovenous malformations and hamartomas

Hamartoma

• Non-neoplastic tumour of normal tissues for the site
• Typically involve blood vessels and melanocytes

Haemangiomas: proliferation of blood vessels

• Capillary (small vessel) can affect the eyelids, orbit and choroid

  • Most common benign orbital tumour in children
  • Typically unencapsulated
  • Phases:
    • Growth phase before 6 months
    • Stable phase
    • Spontaneous involution phase: 1-8 years

• Cavernous haemangiomas (large vessels with septations) are the most common benign orbital tumour in adults

  • Typically encapsulated, low flow lesion
  • Average age of 40
  • Painless
  • Slow growth
  • Axial proptosis
  • Well-defined intraconal lesion on neuroimaging
  • Management:
    • Conservative: observation
    • Excisional biopsy: if unclear diagnosis, threat to vision

• Choroidal haemangiomas: congenital but asymptomatic until adulthood.

  • Circumscribed: no systemic associations. Grow in pregnancy. Poorly demarcated, elevated orange-red choroidal mass at posterior pole. Complicated by fibrous change of the RPE or serous detachment. High internal reflectivity on A-scan US and B-scan shows prominent internal reflections with excavation or orbital shadowing

  • Diffuse: associated with systemic abnormalities eg. Sturge Weber syndrome. Deep red thickened choroid especially at the posterior pole (‘tomato ketchup fundus’). Tortuous retinal vessels

  • Management: photocoagulation and PDT

  • Sturge-Weber syndrome (encephalo-trigeminal angiomatosis) causes extensive haemangiomas. It is a sporadic (not hereditary) mutation in the GNAQ gene

    • Choroidal haemangiomas
    • Vascular proliferation in the angle: glaucoma

Other hamartomas

• Orbital lymphangioma: rare hamartoma of lymph vessels

  • Develops in early childhood
  • Superficial: transilluminating cystic lesion beneath eyelid skin
  • Deep:
    • Non-axial proptosis
    • Acute episodes of spontaneous bleeding (“chocolate cyst”)
    • Does not respond to Valsalva manoeuver, cp. Capillary haemangioma
  • Management
    • Bleomycin injection
    • Careful surgical excision

• Naevi: abnormal proliferation of melanocytes (neural crest derived cells)

  • Found in the conjunctiva, iris, choroid and retina
  • Can occasionally progress to melanoma
  • Benign features: clear margins, no overlying subretinal fluid, no orange pigment/lipofuscin

• Benign astrocytic hamartomas: astrocytes forming a matrix of calcification

  • Associated with tuberous sclerosis (fundal astrocytomas)
  • Stable round nodule projecting into vitreous
  • May simulate retinoblastoma
  • NB: these are one of two optic nerve lesions that exhibit true autofluorescence, the other being drusen.

Summary Table: Haemangiomas

	Capillary	Cavernous
Pathology	Abnormal growth of blood vessels (vascular hamartoma)Low-flow	Encapsulated tumour of large endothelial-lined channelsLow-flow
Patient group	Young children (most common benign orbital tumour in children)F>M	Young adults (most common benign orbital tumour in adults)F>M
Natural course	Spontaneous regression around age 5-7	Progressive slow growth
Associations	Dermal haemangiomas, Kasabach-Merritt syndrome, Maffucci syndrome	Sturge-Weber syndrome (with choroidal haemangiomas)
Signs and symptoms	Superficial lesion: confined to skin, may cause ptosisDeep lesion: non-axial proptosis with valsalva/crying increase in size, reduced vision/amblyopia	Axial proptosis as intraconalHyperopia
CT features	Intra or extra-conal massPoorly defined marginsFeeding vessels	Well defined, encapsulated intraconal tumourContrast enhancingNo feeding vessels
Treatment	Observation unless systemic/ocular complications. Options: intralesional steroid, systemic steroid, oral propranolol, antifibrinolytics, embolisation, radiotherapy, surgical excision	Observation unless complicated/symptomatic

AV fistulae

• Anastomoses between arterial and venous circulations
• High-flow: intracavernous internal carotid artery and cavernous sinus
• Low-flow (“dural shunt”): dural arteries (ie. internal/external carotid branches) and cavernous sinus

Causes

• Congenital: eg. Mason-Wyburn syndrome
• Trauma
• Spontaneous: eg. with hypertension

Clinical features

• High-flow

  • Reduced vision
  • Ophthalmoplegia
  • Audible bruit
  • Pulse-associated tinnitus
  • Pulsatile proptosis
  • Orbital oedema/chemosis
  • Raised IOP
  • RAPD
  • Optic disc swelling
  • Engorgement of retinal veins

• Low-flow

  • Can be asymptomatic
  • Pain
  • Chemosis
  • Raised IOP

Tests

• Orbital imaging via
  • B-scan
  • CT/MRI

Management

• High-flow: catheter embolisation
• Low-flow: may spontaneously close/thrombose