Striatocapsular infarct

Striatocapsular infarcts (SCI), also known as basal ganglionic capsular infarcts, are uncommon infarcts involving the caudate nucleus, putamen, and anterior limb of the internal capsule without any involvement of the cortex, caused by either a complete or partial proximal MCA occlusion.

Epidemiology

Striatocapsular infarcts are uncommon, but also likely under-recognised, with one landmark series reporting 11 cases out of a stroke registry containing 1,600 patients ¹. Risk factors are thought to be more akin with those of thromboembolic cortical ischaemic stroke rather than those of lacunar infarction, with hypertension, smoking, hypercholesterolaemia, carotid stenosis, and atrial fibrillation being important risk factors ^2,3.

Clinical presentation

Although there is a variable presentation, classically patients with striatocapsular infarcts, in the acute phase, exhibit both cortical (e.g. aphasia, sensory neglect or extinction, apraxia) and subcortical (e.g. upper limb hemiparesis, dysarthria) neurological signs, despite the cortex not being directly involved in the infarction ^1-3. The underlying mechanisms for these cortical signs being present in this subcortical striatocapsular infarction are unfortunately not well understood, but isare thought to be due to decreased, but not absent, cortical blood flow, as discussed below ^1-3.

Pathology

Striatocapsular infarcts are defined as infarcts involving the caudate nucleus, putamen, and anterior limb of the internal capsule that are at least 30 mm in length and 10 mm in width, without involvement of the overlying cerebral cortex ^1-3. Although they occur in a similar area to lacunar infarcts, and have previously been described as ‘giant lacunes’ or ‘super lacunes’ ¹, they are not only larger than Miller Fisher’s lacune definition ⁴, but also have a different pathogenesis and clinical phenotype ^1-3.

These infarcts are caused by one of two mechanisms, most often thromboembolic in aetiology ^1-3:

• complete proximal MCA occlusion, or
• partial occlusion of the MCA origin that also blocks lateral lenticulostriate artery origins

However unlike cortical infarcts that may also be due to MCA occlusion, the overlying cortex is not involved in striatocapsular infarcts ^1-3. This is likely either due to either collateral circulation via transcortical and transdural anastomoses, or the partial MCA occlusion still allowing the MCA to be patent enough to supply blood to the cortex ^1-3.

Radiographic features

CT / MRI

Prominent features include:

• infarction of the caudate nucleus, putamen, and anterior limb of the internal capsule ^1-3
• at least 30 mm in length and 10 mm in width in size ³
• have a characteristic ‘comma’ (or lentiform or triangular) shape that is initially hypodense on CT or have increased signal on DWI ^3,5,6 (see ischaemic stroke for radiographical temporal progression of such lesions) 
• no evidence of acute cortical ischaemia ^1-3, although there may be cortical hypoperfusion evident on perfusion studies ⁷

In addition to initial CT or MRI, it may be useful to perform CT angiography, carotid Doppler ultrasound, ECG, as well as other components of the stroke aetiology work-up that would be normally performed for a cortical ischaemic stroke of likely thromboembolic origin ⁶.

History and etymology

The term was coined by Peter Bladin and Samuel Berkovic, Australian neurologists, in their 1984 seminal paper ¹.

Differential diagnosis

• lacunar infarct
• enlarged Virchow-Robin spaces
• cortical ischaemic stroke (clinical differential)