Distinguishing magnetic resonance imaging features between idiopathic hypertrophic pachymeningitis and secondary hypertrophic pachymeningitis

In total, 34 patients were retrospectively collected using searching tools in the picture archiving and communication system (PACS) and hospital information system (HIS) of King Chulalongkorn Memorial Hospital, The Thai Red Cross Society from January 1, 2003 to December 31, 2015. Searching terms included pachymeningitis, dural thickening, thickened dura, and hypertrophic pachymeningitis. Patients who did not have definite diagnosis by laboratory or histopathology, and patients with probable diagnosis by therapeutic diagnosis, who did not have follow-up MRI, were excluded. Patients with dural thickening caused by other entities including intracranial hypotension, post-surgical changes, or dural-based bulky mass were excluded. Our study was approved by the King Chulalongkorn Memorial Hospital Institutional Ethics Committee (certificate of approval no. 754/2015). Informed consent was waived due to retrospective nature of the study.

We collected the image data from MRI Signa Excite 1.5T (General Electric Healthcare, USA), MAGNETOM Aera 1.5T (Siemens Healthcare, Germany), Ingenia 1.5T (Philips Healthcare, Netherlands) and Achieva 3.0T (Philips Healthcare, Netherlands). Imaging comparison included T1-weighted image (T1WI), T2-weighted image (T2WI), diffusion-weighted image (DWI), and gadolinium-enhanced T1WI in all available planes for the data collection and analysis. DWI was not acquired in 11 of 23 idiopathic HP patients and 1 of 11 secondary HP patients.

Dural thickening was defined as maximal dural thickness more than 3 mm of any plane. We collected imaging characteristics of dural thickening: locations (supratentorial, infratentorial, diffuse, and spinal canal; Table 1), configuration (linear/smooth and nodular/undulated), signal intensity comparing to gray matter (hyperintensity, iso-intensity, hypointensity, and dark intensity (equal or less than CSF on T1WI, and equal or less than cortical bone intensity on T2WI), presence of rim pattern (defined as different intensity of the central part and the periphery of the lesions), presence of restricted diffusion, and pattern of enhancement (homogeneous, heterogeneous, and rim).

MR images were individually and blindly reviewed by one diagnostic radiology resident (SW) and one 2-year experienced neuroradiologists (KJ). Disagreement of imaging interpretation was discussed and consensus.

Demographic data, clinical presentation, and each imaging characteristics of each group were described using mean, range, and percentage. Maximal thickness of lesions between two groups was analyzed using T-test. Imaging characteristics between two groups were analyzed using Fisher’s exact test. P < 0.05 was considered statistically significant. Inter-observer reliability was determined using Kappa statistics. Statistical analysis was performed using SPSS 17.0 for Windows (SPSS, Chicago, IL, USA).

Of 34 patients, 23 patients (68%) were idiopathic HP (8 were men, 15 were women with mean age of 46 years (range: 20–68 years). Eight patients had histopathological diagnosis. In all, 15 patients were diagnosed by therapeutic diagnosis. Eleven of 34 patients (32% were classified as secondary HP (4 were men, 7 were women with mean age of 55 years (range: 8–9 years). Secondary HP group included patients who were diagnosed IgG4-related disease, dural metastasis (from prostate cancer), primary dural lymphoma, acute promyelocytic leukemia, nasopharyngeal carcinoma with dural involvement, HIV infection with cryptococcal meningitis, HIV infection with TB meningitis, cavernous sinus thrombosis secondary to orbital cellulitis, meningioma, mastoiditis, and chronic sinusitis. Six of 11 patients had histopathological diagnosis, and 5 of 11 patients were diagnosed by therapeutic diagnosis.

There was no significant difference of age and sex between two groups (Table 2). Headache was present in 15 of 23 (65%) idiopathic HP patients and 2 of 11 (18%) secondary HP patients (P = 0.026). There was no significant difference between duration of headache and presence of neurological deficit. Neurologic deficits were presented in 20 idiopathic HP patients (87%), in 9 secondary HP patients (82%), and were mainly cranial nerve(s) palsy. Optic nerve involvement was the most common neurological deficit in idiopathic HP patients, whereas oculomotor nerve palsy was the most common neurological deficit in secondary HP patients (Table 2). Other neurological symptoms were both arms weakness and left hemiparesis.

In idiopathic HP patients, there were 12 patients (52%) with linear/smooth dural thickening configuration (Figure 1) and 11 patients (48%) with nodular/undulated dural thickening. In secondary HP patients, there were 6 patients (55%) with linear/smooth dural thickening and five patients (45%) with nodular/undulated dural thickening (Figure 2). There was no significant difference in configurations of dural thickening between 2 groups.

Figure 1

Figure 2

Most of dural thickening involved supratentorium in both groups (96% in idiopathic HP group, and all patients in secondary HP group). Secondary HP group significantly had dural thickening at anterior and middle cranial fossae (55%) (Figure 3) as compared to idiopathic HP patients (13%), P = 0.033. There was no secondary HP patient having posterior fossa dural thickening (Table 3).

Figure 3

There was no difference of mean value of maximal dural thickness between idiopathic HP group (5.9 mm) and secondary HP group (5.8 mm) with P = 0.928. There was no significant difference of signal intensity on T1WI, T2WI, and enhancement pattern, and presence of restricted diffusion between two groups.

Three of 23 idiopathic HP patients (13%) showed central hyperintensity and dark intensity rim on T2WI, which was defined as T2-rim pattern (Figure 4). The T2-rim pattern was not found in secondary HP group. Details of MRI findings are in Table 4.

Figure 4

There is significantly found T2 hypointensity and homogeneous enhancement in idiopathic HP (80%) (Figures 1 and 4). None of secondary HP patients had these findings, P = 0.014.

The inter-observer reliability was almost perfect for lesions configuration (k = 1.00), T1 signal intensity (k = 0.879), T2 signal intensity (k = 0.810), and enhancement pattern (k = 0.836).