What is DESH (Diffuse Excessive High Signal) on a CT (Computed Tomography) head scan?

DESH on CT Head: A Marker of Normal Pressure Hydrocephalus

DESH (Disproportionately Enlarged Subarachnoid-space Hydrocephalus) on CT head is a characteristic radiological finding in idiopathic normal pressure hydrocephalus (iNPH), characterized by ventriculomegaly, tight high convexity/midline sulci, and enlarged Sylvian fissures.

Key Features of DESH

• DESH consists of three main components that must be present simultaneously:

  1. Ventriculomegaly (Evans' index ≥ 0.3) 1
  2. Tight medial and high convexity subarachnoid spaces (TMC) 1, 2
  3. Enlarged Sylvian fissures 1, 3

• The tight sulci adjacent to entrapped fluid pockets is a distinguishing feature that helps differentiate DESH from cortical atrophy 3

• DESH represents a structural imaging marker of disordered cerebrospinal fluid (CSF) dynamics 1

Clinical Significance

• DESH is strongly associated with idiopathic normal pressure hydrocephalus (iNPH), a potentially treatable cause of dementia, gait disturbance, and urinary incontinence 3

• DESH findings are often misinterpreted as cortical atrophy, potentially leading to missed diagnoses of treatable iNPH 3

• Patients with DESH show abnormal CSF circulation patterns on nuclear medicine cisternography, including:

  • Higher frequency of radiotracer in the lateral ventricles 1
  • Delayed or absent ascent of radiotracer over the cerebral convexity 1

Development and Progression

• Research suggests that tight medial and high convexity subarachnoid spaces (TMC) is the first change to appear in the development of DESH, occurring in 83.3% of cases with preclinical morphologic features of DESH 2

• The complete DESH pattern develops progressively, with various intermediate stages showing one or two components before the full triad appears 2

Differential Diagnosis

• DESH must be differentiated from:

  • Cerebral atrophy (which shows uniform enlargement of sulci) 3
  • Other causes of ventriculomegaly (obstructive hydrocephalus, ex-vacuo dilatation) 4

• 18F-Fluorodeoxyglucose PET can help differentiate DESH from cortical atrophy in challenging cases 3

Clinical Implications

• Recognition of DESH on CT is crucial as it may identify patients who could benefit from CSF shunting procedures 3

• Following shunt surgery, the entrapped fluid in DESH can diminish, confirming that this finding represents a dynamic CSF process rather than irreversible atrophy 3

• CT head without contrast is not the preferred imaging modality for detailed evaluation of DESH; MRI provides better tissue characterization and may reveal additional features 4

Pitfalls and Caveats

• DESH should not be confused with:

  • The hyperdense middle cerebral artery sign (HMCAS), which indicates arterial occlusion in acute stroke 5
  • Early hypodensities in traumatic brain injury 6
  • Isolated cortical vein thrombosis, which may show different patterns of enhancement 4

• CT has limited soft-tissue characterization compared to MRI, which may limit detailed evaluation of the DESH components 4

• When DESH is suspected on CT, further evaluation with MRI may be warranted for better characterization 1, 3