Giant arachnoid granulation: differential diagnosis of acute headache

Giant Arachnoid Granulations: A Systematic Literature Review

Giant arachnoid granulations (GAGs) are minimally investigated. Here, we systematically review the available data in published reports to better understand their etiologies, nomenclature, and clinical significance. In the literature, 195 GAGs have been documented in 169 persons of varied ages (range, 0.33 to 91 years; mean, 43 ± 20 years; 54% female). Prior reports depict intrasinus (i.e., dural venous sinus, DVS) (84%), extrasinus (i.e., diploic or calvarial) (15%), and mixed (1%) GAG types that exhibit pedunculated, sessile, or vermiform morphologies. GAG size ranged from 0.4 to 6 cm in maximum dimension (mean, 1.9 ± 1.1 cm) and encompassed symptomatic or non-symptomatic enlarged arachnoid granulations (≥1 cm) as well as symptomatic subcentimeter arachnoid granulations. A significant difference was identified in mean GAG size between sex (females, 1.78 cm; males, 3.39 cm; p < 0.05). The signs and symptoms associated with GAGs varied and include headache (19%), sensory change(s) (11%), and intracranial hypertension (2%), among diverse and potentially serious sequelae. Notably, brain herniation was present within 38 GAGs (22%). Among treated individuals, subsets were managed medically (19 persons, 11%), surgically (15 persons, 9%), and/or by endovascular DVS stenting (7 persons, 4%). Histologic workup of 53 (27%) GAG cases depicted internal inflammation (3%), cystic change consistent with fluid accumulation (2%), venous thrombosis (1%), hemorrhage (1%), meningothelial hyperplasia (1%), lymphatic vascular proliferation (1%), and lymphatic vessel obliteration (1%). This review emphasizes heterogeneity in GAG subtypes, morphology, composite, location, symptomatology, and imaging presentations. Additional systematic investigations are needed to better elucidate the pathobiology, clinical effects, and optimal diagnostic and management strategies for enlarged and symptomatic arachnoid granulation subtypes, as different strategies and size thresholds are likely applicable for medical, interventional, and/or surgical treatment of these structures in distinct brain locations.

Giant Arachnoid Granulations: Diagnostic Workup and Characterization in Three Symptomatic Adults

Giant arachnoid granulations (GAGs) are poorly investigated. Here, we document clinical findings associated with five new GAGs and illustrate the anatomical composition of these structures as well as diagnostic considerations in three symptomatic adults. The GAGs ranged from 1.1 to 3.6 cm (mean, 2.2 cm) in maximum dimension and manifested in middle-aged individuals who presented with long-standing brain mass and/or chronic headache. On imaging examinations, the tissues appeared as irregular parasagittal and/or perisinus structures that demonstrated heterogeneous internal elements. The GAGs abutted dura, extended through calvarial marrow spaces, and impinged on dural venous sinuses, causing their stenosis. The histologic workup of two GAG specimens resected from separate individuals revealed central collagen with pronounced internal vascular proliferation. One specimen additionally exhibited reactive changes within the lesion, including venous thrombosis, hemorrhage, and conspicuous inflammation. The salient immune component consisted of a foam cell-rich infiltrate that obstructed subcapsular and internal sinusoidal GAG spaces. Within this specimen, meningothelial hyperplasia was also appreciated. Notably, proliferated lymphatic vascular elements were additionally observed within the structure, extending into deep central collagen regions and engulfing many extravasated erythrocytes in the subcapsular space. In both surgically treated patients, symptoms resolved completely following resection. This report is the first to definitively depict reactive vascular and immunological changes within GAGs that were clinically associated with headache. The frequency of reactive changes within these meningeal structures is unclear in the literature, as GAGs are rarely sampled and investigated. Further systematic analyses are warranted to elucidate the causes and consequences of GAG genesis and their roles in physiology and disease states.

Spontaneous frontal intradiploic meningoencephalocele

Background:

Since 1976, 10 cases of intradiploic encephaloceles have been reported in the literature. This case is the first report of a spontaneous intradiploic meningoencephalocele of the frontal bone hypothesized to be secondary to distant head trauma.

Case Description:

A 60-year-old female with a history of multiple traumatic head injuries as a child presenting with new onset generalized tonic-clonic seizures. Work-up revealed a right frontal epileptic focus. Imaging showed a right frontal intradiploic lesion. The patient underwent surgical resection, which during exploration was found to be an intradiploic encephalocele. She had an uneventful postoperative course with a resolution of seizures.

Conclusions:

The authors hypothesize that the rare nature of posttraumatic frontal intradiploic encephaloceles is due to the increased thickness of the frontal bone compared to the parietal bone.

"Giant" arachnoid granulations just like CSF?: NOT!!

"Giant" AGs (>1 cm) are uncommon and can be misdiagnosed as venous sinus pathology such as a neoplasm or thrombosis. Seventeen patients with a total of 19 venous sinus AGs of >1 cm were collected from contributing authors. MR imaging was available for all AGs; CT, for 5/19; and DSA, for 7/19. Intra-AG fluid was compared with CSF in subarachnoid spaces. Nonfluid AG tissue was compared with gray matter. Diagnosis was based on imaging findings. Fluid within giant AGs did not follow CSF signal intensity on at least 1 MR image in nearly 80% (15/19) of AGs. Nine of these 15 AGs had CSF-incongruent signal intensity on ≥2 MR images. CSF-incongruent signal intensity was seen in 8/8 AGs on FLAIR, 7/10 on precontrast T1WI, 13/19 on T2WI, and 8/14 on contrast-enhanced T1WI. Nonfluid signal intensity was present in 18/19 AGs and varied from absent/hypointense (intra-AG flow voids) to gray matter isointense (stromal tissue).

Giant arachnoid granulation in a patient with benign intracranial hypertension

We report magnetic resonance (MR), computed tomography (CT) and angiographic imaging of an unusual giant arachnoid granulation in the superior sagittal sinus in a man with headache and vertigo. Intrasinus pressure measurements revealed a significant pressure gradient across the lesion. MR imaging is useful to identify giant arachnoid granulation and dural sinus thrombosis, whereas dural sinus pressure measurement in certain cases of giant arachnoid granulations can be used to evaluate the lesion as the cause of the patient's symptoms.