Neuroradiology · Vascular malformations · 1.0

Lawton–Young supplementary AVM grading system

A three-variable supplementary grading scale (age, haemorrhagic presentation, nidus diffuseness) added to the Spetzler–Martin grade to give a supplemented Spetzler–Martin score that better predicts neurological outcome after brain AVM resection.

Purpose

To supplement the Spetzler–Martin grade with patient- and angioarchitecture-related variables not captured by size, eloquence and venous drainage, so that prediction of neurological outcome after microsurgical resection of a brain arteriovenous malformation, and therefore patient selection for surgery, is improved.

Variable	Category	Points
Age (years)	Less than 20	1
Age (years)	20 to 40	2
Age (years)	Greater than 40	3
Presentation	Ruptured (haemorrhagic presentation)	0
Presentation	Unruptured	1
Nidus diffuseness	Compact nidus	0
Nidus diffuseness	Diffuse nidus	1
Supplementary grade total	Sum of the three variables	1 to 5
Supplemented Spetzler–Martin (Supp-SM)	Spetzler–Martin grade (1–5) plus supplementary grade (1–5)	2 to 10

How to use it

The scale is never used alone: it is added to the Spetzler–Martin grade to give a supplemented Spetzler–Martin (Supp-SM) score of 2 to 10, which predicted postoperative neurological outcome better than the Spetzler–Martin grade alone.
The three variables are deliberately different in kind from the Spetzler–Martin components — age reflects healing and plasticity, unruptured status reflects the absence of a haematoma-created dissection plane together with a lower natural-history risk, and diffuseness (an ill-defined nidus with intervening brain parenchyma between vascular channels on angiography and MRI) reflects the difficulty of defining a resection margin.
Unruptured AVMs score a point because they are harder to resect and carry a lower untreated risk, so the threshold for accepting surgical morbidity is higher — this is the item candidates most often reverse.
Deep perforating artery supply was one of the four candidate variables in the derivation study but was not retained in the final three-item scale; later validation cohorts have nonetheless found it an independent predictor of unfavourable outcome, so it remains an operative consideration outside the score.
A Supp-SM score of 6 is the conventional cut-off for acceptable surgical risk, with scores of 6 or less favouring resection and scores above 6 favouring conservative or alternative management; this is a decision aid to be weighed against natural-history risk, not a treatment mandate.

Common mistake

Assigning the presentation point the wrong way round — giving 1 point for a ruptured AVM instead of for an unruptured one — and quoting the supplementary grade in isolation rather than as an addition to the Spetzler–Martin grade.

Exam pearl

Supplementary grade = Age (1/2/3) + Unruptured (1) + Diffuse (1), range 1–5; added to Spetzler–Martin gives Supp-SM 2–10, cut-off 6.

Viva questions

What are the three components of the Lawton–Young supplementary AVM grade?: Patient age, haemorrhagic presentation and nidus diffuseness. Age under 20 scores 1, 20 to 40 scores 2 and over 40 scores 3; an unruptured presentation scores 1 and a ruptured one scores 0; a diffuse nidus scores 1 and a compact nidus scores 0.
What is the range of the supplementary grade and of the supplemented Spetzler–Martin score?: The supplementary grade runs from 1 to 5. Added to the Spetzler–Martin grade of 1 to 5, the supplemented Spetzler–Martin score runs from 2 to 10, giving nine possible grades.
Why does an unruptured AVM score a point rather than a ruptured one?: A ruptured AVM has a haematoma cavity that provides a dissection plane and has already declared a high natural-history risk, so surgery is technically easier and more readily justified. An unruptured AVM lacks that plane and carries a lower untreated risk, so it is the less favourable surgical scenario and attracts the point.
There was a fourth variable considered in the original study. What was it, and is it in the scale?: Deep perforating artery supply. It was one of the candidate factors in the derivation study but was not retained in the final three-item scale, although later validation series have found it an independent predictor of unfavourable surgical outcome.
What Supp-SM score is used as a threshold for surgery, and how should it be applied?: A Supp-SM of 6 is the conventional cut-off, with 6 or less favouring resection and above 6 favouring conservative or alternative management. It is a risk-stratification aid to be weighed against the untreated natural-history risk and multidisciplinary options, not an automatic rule.
Why was a supplementary scale needed when the Spetzler–Martin grade already exists?: The Spetzler–Martin grade uses only size, eloquence and deep venous drainage, and groups most operated patients into grades 2 and 3 without discriminating outcome within them. The supplementary variables add patient and angioarchitectural information, and the combined score predicted postoperative neurological outcome better than the Spetzler–Martin grade alone in both the derivation and an independent validation cohort.
What is the main pitfall in applying this system?: Quoting the supplementary grade on its own rather than as an addition to the Spetzler–Martin grade, or reversing the presentation point by scoring the ruptured AVM.