Diagnostic performance of black tent sign on 3D T2 SPACE in the diagnosis of idiopathic normal-pressure hydrocephalus.

Abstract

Purpose: Idiopathic normal-pressure hydrocephalus (iNPH) presents with Hakim's triad and diagnosis is solely based on clinical findings. The role of imaging is confined to the detection of ventriculomegaly and the exclusion of other possible entities. Hyperdynamic CSF flow has been demonstrated in various flow-related imaging studies. In this study, we aimed to investigate the diagnostic performance of the "black tent" sign in the CSF flow-sensitive T2 SPACE sequence.

Materials and methods: This retrospective study includes 22 patients diagnosed with iNPH who underwent CSF shunting and benefited from the procedure and showed clinical recovery. The control group consisted of 38 patients with excluded diagnoses of iNPH by clinical examination and follow-up. T2 SPACE images from both groups were assessed according to the presence of the "black tent" which was defined as a signal void detected on the T2 SPACE image traced along the borders of the fourth ventricle and filling the triangular area of the median dorsal recess. The diagnostic performance of the sign was calculated, and the results were compared with those of Evan's Index, callosal angle, and disproportionately enlarged subarachnoid spaces.

Results: The diagnostic performance of the black tent sign in diagnosing iNPH was determined with a sensitivity of 90.91%, specificity of 78.95%, PPV of 71.43%, NPV of 93.75%, and overall accuracy of 83.33%. The sign showed better diagnostic performance in participants over 60 years in which sensitivity, specificity, PPV, NPV, and accuracy increased to 86.67%, 93.75%, 86.67%, 99.75%, and 91.49% respectively. Diagnostic performance of the sign was superior to DESH (p = 0.007).

Conclusion: The black tent sign observed in T2 SPACE images in CSF flow MRI studies correlates with the diagnosis of iNPH with high sensitivity and specificity.