Radiation Oncology: A Question-Based Review

Arteriovenous Malformation

Boris Hristov and Daniele Rigamonti

image Background

What is the avg age at presentation for arteriovenous malformations (AVMs)?

The avg age at presentation for AVMs is 30 yrs.

What is the nidus of an AVM?

The nidus is a tangle of abnl arteries/veins connected by at least 1 fistula.

What is the main histologic abnormality in the vasculature of an AVM?

Absence of smooth muscle layer; ↑ venous pressure (fibromuscular thickening with incomplete elastic lamina)

What is the morbidity and mortality per bleed for AVMs?

1.     Morbidity: 30%–50%/bleed

2.     Mortality: 5%–10%/bleed (1%/yr)

What is the rate of hemorrhage per yr for AVMs?

AVMs have a 2%–4% chance of hemorrhage/yr.

Are most AVM cases familial or sporadic?

Most AVMs are sporadic.

What familial/genetic syndromes are associated with AVMs?

Osler-Weber-Rendu and Sturge-Weber syndromes are associated with AVMs.

What characteristics portend an increased risk of hemorrhage from AVMs?

Previous hemorrhage, aneurysm, deep venous sinus drainage, deep location, single draining vein, and venous stenosis

Aneurysms are found in what % of pts with AVMs?

6%–8% of AVM pts harbor aneurysms.

image Workup/Staging

What are common presenting signs of AVMs?

Intracerebral hemorrhage (42%–72%) > seizures and HA

What imaging modality is ideal to r/o a bleed?

CT is ideal to r/o cerebral bleeds.

What is the gold standard imaging modality for AVMs?

Angiography is the gold standard modality for imaging AVMs.

What other imaging modalities can be used for AVMs? What are their advantages?

CT angiography (good vascular detail), MR angiography (good anatomy detail), functional MRI (eloquent areas), and diffusion tensor imaging (for white matter tracts)

What scale is used to evaluate AVM pts for surgery?

Spetzler-Martin scale/grading system (totals possible: I–V)

What 3 AVM characteristics in the Spetzler-Martin scale are predictive of surgical outcomes?

AVM characteristics that predict surgical outcome:

1.     Diameter (<3 cm = 1, 3–6 cm = 2, >6 cm = 3)

2.     Location (noneloquent area = 0, eloquent area = 1)

3.     Pattern of venous drainage (superficial = 0, deep = 1)

How does AVM diameter/size scoring correlate with surgical outcomes?

The smaller the AVM diameter/size (<3 cm), the better the outcomes.

What brain areas are considered eloquent?

Eloquent areas include sensorimotor, language, visual, thalamus, hypothalamus, internal capsule, brain stem, cerebellar peduncles, and deep cerebellar nuclei.

image Treatment/Prognosis

What are the 3 Tx options for AVMs?

Surgery, radiosurgery, and embolization

What is the goal of Tx with AVMs? Why?

Complete obliteration is the goal, since there is no benefit/↑ risk of bleed if the obliteration is partial.

Which lesions are most amenable to surgery?

Those with low (I–III) Spetzler-Martin scores are most amenable to surgery.

What is frequently done for grade III lesions before surgery?

Embolization can be performed for grade III lesions before surgery.

What is the main advantage of surgery?

The main advantages of surgery are immediate cure and reduction in the risk of hemorrhage.

For which AVM lesions is radiosurgery (SRS) preferred?

Radiosurgery is preferred for lesions <3 cm that are located in deep or eloquent regions of the brain.

What is the main disadvantage of SRS for AVMs?

The main disadvantage of SRS is the lag time of 1–3 yrs to complete obliteration (i.e., continued bleeding risk).

How does RT lead to AVM obliteration?

Vascular wall thickening and luminal thrombosis from RT effect result in obliteration of the AVM.

Is the bleeding risk completely eliminated after SRS?

No. It is reduced by ~88% but not eliminated. (Maruyama K et al., NEJM 2005)

On what do SRS cure rates for AVMs primarily depend?

Size of AVM: 81%–91% if <3 cm, lower if >3 cm (Maruyama K et al., NEJM 2005)

What can be done for high-grade AVMs (IV–V) not amenable for surgery?

Staged SRS (different components targeted at separate sessions) (Sirin S et al., Neurosurg 2006)

For which AVMs can embolization be curative?

AVMs <1 cm that are fed by a single artery can be cured by embolization alone.

How are AVMs with feeding artery aneurysms managed?

If the aneurysm is >7 mm in diameter, clip or coil the aneurysm 1st, then treat the AVM. The aneurysm is at greater risk for rupture if the AVM is treated 1st.

What is the ongoing randomized ARUBA trial investigating?

The ARUBA trial is investigating Tx vs. conservative management for unruptured AVMs.

What SRS doses are commonly used for AVMs?

1.     Lesions <3 cm21–22 Gy to 50% IDL. If the lesion is in the brain stem, lower the dose to ≤16 Gy.

2.     Lesions >3 cm16–18 Gy to 50% IDL

image Toxicity

What are the reported rates of permanent weakness or paralysis, aphasia, and hemianopsia for grade I–III AVM pts treated with surgery?

The rate of serious postsurgical complications is 0%–15% (depending on the series).

What are common early and delayed complications after SRS for AVMs?

1.     Early: seizures, n/v, HA

2.     Delayed: seizures, hemorrhage, radionecrosis/edema, venous congestion

What is the incidence of transient vs. permanent neurologic complications after SRS for AVMs?

Complications after SRS for AVMs are as follows: transient (5%) vs. permanent (1.4%).

On what 2 factors do complication rates after SRS for AVMs primarily depend?

Size of AVM and RT dose are the primary determinants of complications after SRS.

What does the follow-up entail after Tx for AVMs?

Adequate follow-up includes routine H&P + MRI q6mos for 1–3 yrs, then annually.

What study needs to be performed once the MRI shows evidence of AVM obliteration?

An angiogram needs to be performed (in addition to MRI) to confirm complete AVM obliteration.