Houk Jessica L, Amrhein Timothy J, Gray Linda, Malinzak Michael D, Kranz Peter G
1Department of Radiology, Division of Neuroradiology, Duke University Medical Center, Durham, North Carolina.
J Neurosurg. 2021 Oct 29;136(6):1796-1803. doi: 10.3171/2021.6.JNS211010. Print 2022 Jun 1.
Chiari malformation type 1 (CM-1) and spontaneous intracranial hypotension (SIH) are causes of headache in which cerebellar tonsillar ectopia (TE) may be present. An accurate method for differentiating these conditions on imaging is needed to avoid diagnostic confusion. Here, the authors sought to determine whether objective measurements of midbrain morphology could distinguish CM-1 from SIH on brain MRI.
This is a retrospective case-control series comparing neuroimaging in consecutive adult subjects with CM-1 and SIH. Measurements obtained from brain MRI included previously reported measures of brain sagging: TE, slope of the third ventricular floor (3VF), pontomesencephalic angle (PMA), mamillopontine distance, lateral ventricular angle, internal cerebral vein-vein of Galen angle, and displacement of iter (DOI). Clivus length (CL), an indicator of posterior fossa size, was also measured. Measurements for the CM-1 group were compared to those for the entire SIH population (SIHall) as well as a subgroup of SIH patients with > 5 mm of TE (SIHTE subgroup).
Highly significant differences were observed between SIHall and CM-1 groups in the following measures: TE (mean ± standard deviation, 3.1 ± 5.7 vs 9.3 ± 3.5 mm), 3VF (-16.8° ± 11.2° vs -2.1° ± 4.6°), PMA (44.8° ± 13.1° vs 62.7° ± 9.8°), DOI (0.2 ± 4.1 vs 3.8 ± 1.6 mm), and CL (38.3 ± 4.5 vs 44.0 ± 3.3 mm; all p < 0.0001). Eight (16%) of 50 SIH subjects had TE > 5 mm; in this subgroup (SIHTE), a cutoff value of < -15° for 3VF and < 45° for PMA perfectly discriminated SIH from CM-1 (sensitivity and specificity = 1.0). DOI showed perfect specificity (1.0) in detecting SIH among both groups. No subjects with SIH had isolated TE without other concurrent findings of midbrain sagging.
Measures of midbrain sagging, including cutoff values for 3VF and PMA, discriminate CM-1 from SIH and may help to prevent misdiagnosis and unnecessary surgery.
1型Chiari畸形（CM-1）和自发性颅内低压（SIH）是可能伴有小脑扁桃体下疝（TE）的头痛病因。需要一种在影像学上区分这些病症的准确方法，以避免诊断混淆。在此，作者试图确定中脑形态的客观测量指标能否在脑部MRI上区分CM-1和SIH。
这是一项回顾性病例对照研究，比较了连续的成年CM-1和SIH患者的神经影像学表现。从脑部MRI获得的测量指标包括先前报道的脑下垂测量指标：TE、第三脑室底斜率（3VF）、脑桥中脑角（PMA）、乳头体脑桥距离、侧脑室角、大脑内静脉-大脑大静脉角以及中脑导水管移位（DOI）。还测量了斜坡长度（CL），作为后颅窝大小的指标。将CM-1组的测量结果与整个SIH人群（SIHall）以及TE>5mm的SIH患者亚组（SIHTE亚组）的测量结果进行比较。
在以下测量指标上，SIHall组和CM-1组之间观察到高度显著差异：TE（平均值±标准差，3.1±5.7 vs 9.3±3.5mm）、3VF（-16.8°±11.2° vs -2.1°±4.6°）、PMA（44.8°±13.1° vs 62.7°±9.8°）、DOI（0.2±4.1 vs 3.8±1.6mm）和CL（38.3±4.5 vs 44.0±3.3mm；所有p<0.0001）。50例SIH患者中有8例（16%）的TE>5mm；在该亚组（SIHTE）中，3VF<-15°和PMA<45°的截断值能完美区分SIH和CM-1（敏感性和特异性=1.0）。DOI在两组中检测SIH时显示出完美的特异性（1.0）。没有SIH患者仅有孤立的TE而无其他中脑下垂的并发表现。
中脑下垂的测量指标，包括3VF和PMA的截断值，可区分CM-1和SIH，可能有助于防止误诊和不必要的手术。
