Temporal Bone Thickness Research Articles

The Thickness of the Temporal Squama and Its Implication for Transcranial Sonography

The difficult transtemporal ultrasound window is a relatively frequent occurrence. The authors assessed if the thickness of the temporal bone squama as measured in the "bone window" of the head computerized tomography (CT) scan can predict the transtemporal acoustic window. The authors retrospectively reviewed the head CTs on their bone window setting of patients in which nonimaging transcranial Dopplers (TCDs) had been performed. The thickness of the temporal squama in its thinnest portion was measured. The temporal TCD windows were graded in three classes: class 1 as good, class 2 when only a partial study is possible, and class 3 as an impossible ultrasonic window. In a case-control design, for every patient with any class 2 and 3 TCD temporal window, a patient with a class 1 window was randomly included from the same time period. Fifty-five temporal bones (56%) were class 1, 17 (17%) were class 2, and 27 (27%) were class 3. Bone thicknesses (in mm, mean +/- SD) were greater in those with poorer windows: class 1 = 2.67 +/- 0.70, class 2 = 4.06 +/- 0.56, and class 3 = 5.04 +/- 1.06, P < or = .0001 by Cusick's nonparametric test of trend. Temporal squama thickness of > or = 5 mm portends 86% sensitivity, 90% specificity, 70% positive predictive value, and a positive likelihood ratio of 8.6 for a class 3 transtemporal ultrasound window. Measurement of temporal bone thickness on the bone window setting of the head CT scan may be useful in identifying patients who are poor candidates for transcranial ultrasound.

Insufficient and absent acoustic temporal bone window: Potential and limitations of transcranial contrast-enhanced color-coded sonography and contrast-enhanced power-based sonography

The aim of this study was to investigate the diagnostic potential of contrast-enhanced transcranial color-coded sonography (CE-TCCS) and contrast-enhanced transcranial power-based sonography (CE-TPS) in patients with insufficient or absent acoustic bone windows (IABW). Due to temporal bone thickness, the basal cerebral circulation could not be insonated in 21 of 172 patients using unenhanced transcranial color-coded real-time sonography (TCCS) and transcranial power-based sonography. Additional CE-TCCS and CE-TPS were performed after application of 400 mg/ml galactose microbubble suspension. In both modalities, the use of echo-contrast agents allowed visualisation of the first segment of the middle cerebral artery (MCA) in all patients. The A1 segment of the anterior cerebral artery (67% in CE-TCCS; 81% in CE-TPS), P1 segment of the posterior cerebral artery (71% in CE-TCCS; 76% in CE-TPS) and the basilar artery (48% in CE-TCCS; 67% in CE-TPS) were depictable in the majority of the examinations. The M3 (5% in CE-TCCS; 33% in CE-TPS; p < 0.05), P2 (24% in CE-TCCS; 71% in CE-TPS; p < 0.005), P3 segments (0% in CE-TCCS; 43% in CE-TPS; p < 0.005) and the posterior communicating artery (5% in CE-TCCS; 33% in CE-TPS; p < 0.05) were detected in a significantly greater proportion of subjects using power Doppler. In conclusion, CE-TCCS and CE-TPS appear to be sensitive ultrasonic tools that provide reliable data regarding the basal cerebral circulation in patients with IABW. Furthermore, CE-TPS offers advantages over CE-TSSC in the identification of small-caliber arteries and vessels that run at unfavorable angels to the ultrasound beam. Both methods can overcome hyperostosis of the skull that is a major hindrance in transcranial ultrasonography, and may be helpful in the diagnosis of occlusive diseases of intracranial vessels.

A Study on Detectability of Intracranial Blood Flow by TCD

[Purpose] It has been reported that the failure rate in recording middle cerebral artery (MCA) flow ranged from 20 to 40%. In our experience, this failure rate was about 10%. The detectability of MCA by transcranial Doppler ultrasonography (TCD) is influenced by several factors: (1) temporal bone thickness. (2) blood flow velocity. (3) pulsatility index. (4) age and sex of patients. (5) branching type of the MCA. (6) hematocrit, PaCO2, systolic blood pressure of the patients. and (7) technique. In this study, we investigated the detectability in 58 vessels of 33 subjects to assess the factors that affect Doppler detectability by TCD. [Materials and Methods] We analyzed three groups classified by the detectability, namely group A (easy detection) and group B (can detect MCA flow within 10 minutes) or group C (impossible to detect) . [Results] The significant factors that influenced the measurement of MCA flow were as follows: presence of thick temporal bone, a low flow velocity, and being an elderly female. The other factors had no apparent significance due to different conditions. [Conclusion] Thickness of the skull and blood flow velocity were considered to be two major factors that make it difficult to detect intracranial blood flow by TCD.