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Arachnoid Granulations and “Giant” Arachnoid Granulations

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Arachnoid Granulations and “Giant” Arachnoid Granulations View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by RERO DOC Digital Library Surg Radiol Anat (2008) 30:417–421 DOI 10.1007/s00276-008-0345-2 ORIGINAL ARTICLE Dural arachnoid granulations and “giant” arachnoid granulations Johannes Haybaeck · Rene Silye · Dov SoVer Received: 4 March 2008 / Accepted: 17 March 2008 / Published online: 8 April 2008 © Springer-Verlag 2008 Abstract Although arachnoid granulations (AGs) were Introduction already described by Antonio Pacchioni more than 300 years ago, two issues draw particular attention: Wrst, Although arachnoid granulations (AGs) were initially the radiological features and diVerential diagnosis of the so- described by Antonio Pacchioni more than 300 years ago called giant AGs (GAGs) and second, their possible associ- [1], they are still poorly described, especially in the neuro- ation with various disease processes. In order to evaluate radiological literature. Two issues draw particular attention: the frequency, size and normal distribution of GAGs, an Wrst, the radiological features of AGs, particularly of the so- anatomical study of the dural sinuses was carried out. It called giant AGs (GAGs) and its diVerential diagnosis [2– involved all the autopsies performed during the period 11], and second, their possible association with various dis- August 2002–February 2005 and included 651 cases: 306 ease processes [12–14]. Giant AGs are still a poorly under- females and 345 males, aged 13–99 years (mean 69 years). stood distinct entity, seldom mentioned in the Grossly visible GAGs were identiWed in 24 cases: 7 neuroanatomical and neuropathological literature. Men- females and 17 males, aged 45–92 years (mean 69 years). ingothelial hyperplasia is often confused with it. In the lat- This is the largest population-based anatomical study on ter, putative predisposing factors were recently described GAGs. It shows that GAGs, in general a rare Wnding and included hemorrhage, chronic renal disease, old age, (3.68%), are rather common in the adult population, espe- trauma, and an adjacent optic nerve pilocytic astrocytoma. cially in the elderly (aged >65 years) and that they can Furthermore, a discontinuous growth pattern is well known. reach remarkable size (up to 2.5 cm and more in diameter). By deWnition, meningothelial hyperplasia is a non-invasive Giant AGs should be considered in the radiological diVer- process involving the arachnoid mater, which can exist in ential diagnosis of intradural lesions, particularly those near proximity to normal tissue or is even surrounded by occurring in the transverse sinus of the elderly. intact structures [15]. In order to evaluate the frequency, site, size and normal Keywords Giant arachnoid granulations · distribution of GAGs, an examination of the dural sinuses Transverse sinus · Epidemiology was carried out in 651 autopsy cases. In 3.68% of the cases GAGs were found; their morphology and pathophysiologi- cal relevance will be discussed. J. Haybaeck · R. Silye Department of Pathology and Neuropathology, Materials and methods State Neuropsychiatric Hopsital Wagner-Jauregg, Wagner-Jauregg-Weg 15, 4020 Linz, Austria In order to evaluate the frequency, size as well as age and J. Haybaeck (&) · D. SoVer sex distribution of GAGs, an anatomical study of the dural Institute of Neuropathology, Department of Pathology, sinuses was carried out. It involved all the autopsies per- University Hospital Zürich, Schmelzbergstrasse 12, 8091 Zurich, Switzerland formed in the Wagner Jauregg Hospital, Linz, Austria, and e-mail: [email protected] its aYliated hospitals in Upper Austria, during the period 123 418 Surg Radiol Anat (2008) 30:417–421 August 2002–February 2005. The study population 69 years). Grossly visible GAGs were identiWed in 24 included 651 cases: 306 females and 345 males, aged 13– patients: 7 females and 17 males, aged 45–92 years (mean 99 years (mean 69 years). 69 years). No GAGs were observed in individuals younger The skull was opened in the usual manner and removed than 45 years; 20.8% of patients with GAGs were under the carefully, leaving the dura mater intact and covering the age of 65 while 79.2% were 65 years of age and older. The brain. Then all intracranial sinuses were opened with scis- age-speciWc incidence of our cases was: group 1: sors and carefully inspected. Any region suspicious for the <65 years: 36.4%, group 2: ¸65 years: 63.6% out of entire presence of GAGs, was documented photographically, then autopsies with an overall incidence of 2.9%. A histogram excised and processed for histology and subsequent immu- showing the age distribution of these lesions in the entire nohistochemistry. Thus, the specimens were Wxed in a 4% cohort by decade is shown in Table 1; the age distribution formaldehyde solution for 48 h being aYxed to a piece of of individuals with the deWnite diagnosis of GAGs in per- cork. The histological examination encompassed the fol- centage is presented in Table 2. lowing stainings: H&E, Elastica van Giesson. Immunohis- All GAGs were found exclusively in the transverse tochemistry was performed on formalin-Wxed and paraYn- sinus, usually adjacent to the transverse/sigmoid sinus junc- embedded, 5-m-thick sections on adhesive-coated glass. tion (Fig. 1). In 13 cases (54.1%) GAGs were found bilater- DeparaYnized, rehydrated sections underwent antigen ally, while in the remaining cases they were almost equally retrieval using 2 mmol/l HCl for 20 min in a water bath at divided between the right (5 cases) and the left transverse 95–100°C. All subsequent steps were carried out using the sinus (6 cases). DAKO Autostainer Immunostaining System (DAKO S5007) and the EnVison™+ kit (code K4007, DakoCyto- mation, Carpinteria, CA, USA). The sections were treated Table 1 Histogram showing the age distribution of prevalence of with 3% H2O2 for 5 min to block endogenous peroxidase giant AGs in the entire cohort by decade followed by protein block for 5 min. The primary antibod- ies, purchased from DAKO were directed agianst vimentin, desmin, epithelial membrane antigen (EMA), S100. The sections were incubated with the secondary antibodies for 30 min. The reaction product was visualized using diam- inobenzidine chromogen (liquid DAB+, K3468, DakoCyto- mation, Carpinteria, CA, USA) for 5 min. Then, the sections were counterstained with Mayer’s Haemalaun solution. As a second step slides were treated with an enzyme-linked antibody using the system Envision™ DAKO ChemMAT™ Detection Kit followed by peroxi- dase/chromogene DAB (rabbit/mouse). The following anti- bodies were used: vimentin (dilution 1:1,000), actin (dilution 1:400), desmin (1:50), S100 protein (dilution 1:800), MiB-1 (dilution 1:200). W The lesions were then classi ed as AGs or GAGs Table 2 Histogram showing the age distribution of prevalence of gi- according to criteria published in the literature as follows: ant AGs in the positive cases by decade AGs are small protrusions of the arachnoid through the dura. Giant AGs are much larger than normal AGs, approx- imately 10 mm in diameter. Immunohistochemistry was evaluated by two indepen- dent assessors (J. H. and R. S.) using light microscopy. Fur- thermore, clinical histories were evaluated with regard to the existence of other diseases/disorders in order to Wnd a correlation with other diseases. Results The size of the examined sample encompassed 651 cases: 306 females and 345 males, aged 13–99 years (mean age: 123 Surg Radiol Anat (2008) 30:417–421 419 Fig. 1 a, b Examples of “giant” AGs (GAGs) in the left trans- verse sinus underneath the skull of the posterior cranial fosse (macroscopy). c GAG stained with an antibody against vimen- tin (£20) Grossly, GAGs appeared as partly gelatinous, partly Discussion white-yellowish shiny lobular protrusions into the sinus lumen, usually at sites of cortical venous entrance into the To the best of our knowledge, this is the largest population- sinus (Fig. 1). Their size ranged from 1 mm to 29 mm in based anatomical study on GAGs. It shows that GAGs are diameter (mean 6 mm), with more than one third of the rather common in the adult population, especially in the GAGs (37.6%) being larger than 10 mm in diameter, quali- elderly (aged >65 years) and they can reach remarkable fying as “giant AGs” (size distribution: up to 2.5 mm: proportions (up to 2.5 cm and more in diameter). Giant 12.5%; 2.6–5 mm: 20.8%; 5.1–7.5 mm: 12.5%; 7.6 mm– AGs should be considered in the radiological diVerential 10 mm: 16.6%; >10.1 mm: 37.6%). We could neither Wnd a diagnosis of intradural lesions, particularly those occurring correlation of the size of the GAGs with the age of the in the transverse sinus of the elderly. Interestingly, grossly patients nor of the presence of malignancies or severe car- visible GAGs were exclusively found in individuals older diovascular problems and enlarged AGs or any further dis- than 45 years, which could be a hint for a degenerative pro- eases. Histologically, GAGs were composed of dense cess. Because we could not Wnd in any of the cases a direct collagenous connective tissue admixed with clusters of association with the patient’s illness or the cause of death arachnoid cells and a network of delicate vascular spaces, this observation represents more a normal anatomic Wnding covered by an endothelial cell layer. Histology showed vas- rather than a pathologic process. The occurrence of GAGs cular, cell-free spaces beside broad arachnoidal and dural should be considered in the diVerential neuroradiological collagenous bands (Figs. 1, 2). diagnosis of meningiomas, especially benign meningiomas On microscopic examination of proliferations in the because of their similarity to such lesions [14, 15]. This transverse sinus diagnosed on autopsy in 24 patients, a pos- becomes more crucial, when they are seen in close contact itive reaction for vimentin could be shown in collagenous, with the skull bone or with the dura mater.
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