In the March 2013 issue of the Journal, we read with great interest the articles dealing with various disorders initially thought to be idiopathic intracranial hypertension, including spinal leptomeningeal lymphoma (1) and Sheehan syndrome (2). We describe a rare case of pseudotumor cerebri (PTC), associated with a giant arachnoid granulation (GAG) in the transverse venous sinus.
A 26-year-old healthy, nonobese man complained of horizontal diplopia for 1 month. Visual acuity was 20/25 in each eye, pupillary reactions were normal, and ocular motility revealed bilateral abduction deficits. Funduscopy demonstrated bilateral papilledema, and automated visual fields showed enlarged blind spots. Optical coherence tomography of the peripapillary retinal nerve fiber layer (RNFL) confirmed optic disc edema, with average RNFL thickness of 171 μm for the right eye and 275 μm for the left eye.
Computed tomography (CT) of the brain revealed no mass lesion or hydrocephalus but a hypodense filling defect at the origin of the right transverse sinus (Fig. 1A). Contrast-enhanced magnetic resonance imaging (MRI) and magnetic resonance venography confirmed a 3.5-cm filling defect, noted to be isointense to cerebrospinal fluid (CSF) (Fig. 1B, C). Because these findings initially were interpreted as subacute or chronic venous sinus thrombosis, a hypercoagulability work-up was initiated and the patient was started on daily aspirin (81 mg). On further review of the neuroimaging studies and based on the filling defect being isointense to CSF, the diagnosis was changed to GAG of the transverse sinus.
Lumbar puncture revealed an elevated opening pressure of 56 cm water, with normal CSF composition. The diagnosis of PTC was made, and treatment was initiated with oral acetazolamide 500 mg twice daily. Despite titrating doses of acetazolamide up to 1,000 mg twice daily, the patient's diplopia persisted, and he developed more severe headaches with worsening papilledema.
Because of progressive symptoms and signs, intervention via an endovascular approach was offered to the patient. Cerebral venography revealed intact venous flow around the intraluminal obstruction in the right transverse sinus. Manometry showed pressure proximal to the GAG of 14 mm Hg and 3 mm Hg distal to the GAG. Because the appearance and pressures within the left transverse and superior sagittal sinuses were normal, stenting was not performed.
The patient continued on medical treatment alone, with his doses of acetazolamide increased to 1,000 mg 3 times daily. A repeated lumbar puncture showed opening pressure of 32 cm water. His headaches and papilledema slowly improved and were resolved by 6 months. Repeat MRI revealed no change in the size of the hypodense filling defect in the right transverse sinus.
Arachnoid granulations filter CSF across the lining of the arachnoid into the cerebral venous system. GAGs are believed to be a normal variant (3,4), with an estimated prevalence of 0.3%–1.0% in adults (4).
GAGs may mimic other entities and may be misdiagnosed as venous sinus thrombosis. However, venous sinus thrombosis is hyperintense on both CT and T1 axial MRI and enhances with contrast. Alternatively, GAGs are hypointense on CT and T1 axial MRI and do not enhance (4).
Although usually asymptomatic, GAGs have been reported in association with increased intracranial pressure (ICP) and PTC in only a handful of cases (5–8). Arjona et al (6) described a 51-year-old nonobese man who presented with transient visual obscurations and bilateral papilledema. The patient was found to have a GAG at the right transverse sinus–sigmoid sinus junction, with hypoplasia of the left transverse sinus. Opening pressure on lumbar puncture was 27 cm water. Unfortunately, the authors did not discuss the management of this case but believed GAG to be responsible for the elevated ICP. Choi et al (7) reported a 66-year-old woman with occipital headaches who was initially diagnosed as having dural sinus thrombosis. MRI confirmed the diagnosis of GAG, and a normal venous pressure gradient was found across the symptomatic lesion. The patient's headaches were managed with medical therapy. Zheng et al (8) described a unique case of a patient with GAG in the dominant left transverse sinus and elevated pressure proximal to the GAG. Stenting of the transverse sinus reduced the pressure gradient across the lesion, as well as the ICP, and led to symptomatic improvement.
The cause of GAG formation is uncertain. It has been postulated that increased CSF volume and pressure may cause hypertrophy of the arachnoid granulations, with subsequent formation of a GAG (4). However, if this were the case, then many more patients with ICP from various etiologies would develop GAGs. Alternately, they may represent hyperplasia of preexisting arachnoid granulations or benign neoplasm of mesenchymal origin (3).
The clinical course of our patient raises the question of whether the GAG caused PTC or whether its presence was purely coincidental. Normal venous sinus pressures proximal to the GAG make it less likely that GAG raised venous sinus pressure and led to increased ICP. With medical therapy alone, PTC completely resolved in our patient. There is still the possibility that the GAG had caused increased ICP, and venous collaterals developed with time, facilitating venous outflow. We did not perform a follow-up cerebral venogram after our patient's PTC resolved to evaluate this possibility.
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2. Moodley KK, Broad R, Chung K, Riordan-Eva P, Sibtain NA, Moran NF. Sheehan syndrome associated with raised intracranial pressure. J Neuroophthalmol. 2013;33:54–57.
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7. Choi HJ, Cho CW, Kim YS, Cha JH. Giant arachnoid granulation misdiagnosed as transverse sinus thrombosis. J Korean Neurosurg Soc. 2008;43:48–50.
8. Zheng Z, Zhou M, Zhao B, Zhou D, He L. Pseudotumor cerebri syndrome and giant arachnoid granulation: treatment with venous sinus stenting. J Vasc Interv Radiol. 2010;21:927–929.