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

Intravenous arachnoid granulation hypertrophy in patients with Parkinson disease

Intravenous arachnoid granulations (AGs) are protrusions of the arachnoid membrane into the venous lumen and function as contributors to the cerebrospinal fluid (CSF) flow circuit. Patients with Parkinson disease (PD) often present with accumulation of alpha synuclein. Previous works have provided evidence for neurofluid circulation dysfunction in neurodegenerative diseases associated with changes in CSF egress, which may have implications regarding AG morphology. The present study aims to investigate group differences in AG volumetrics between healthy and PD participants, as well as relationships between AG characteristics and clinical assessments. Generalized linear models revealed significant increases in AG volumetrics and number in PD compared to healthy controls. Partial Spearman-rank correlation analyses demonstrated significant relationships between AG metrics and motor and cognitive assessments. Finally, AG volumetrics were positively correlated with objective actigraphy measures of sleep dysfunction, but not self-report sleep symptoms.

Imaging of pediatric skull lytic lesions: A review

Skull lesions in pediatric population are common findings on imaging and sometimes with heterogeneous manifestations, constituting a diagnostic challenge. Some lesions can be misinterpreted for their aggressiveness, as with larger lesions eroding cortical bone, containing soft tissue components, leading to excessive and, in some cases, invasive inappropriate etiological investigation. In this review, we present multiple several conditions that may present as skull lesions or pseudolesions, organized by groups (anatomic variants, congenital and development disorders, traumatic injuries, vascular issues, infectious conditions, and tumoral processes). Anatomic variants are common imaging findings that must be recognized by the neuroradiologist. Congenital malformations are rare conditions, such as aplasia cutis congenita and sinus pericranii, usually seen at earlier ages, the majority of which are benign findings. In case of trauma, cephalohematoma, growing skull fractures, and posttraumatic lytic lesions should be considered. Osteomyelitis tends to be locally aggressive and may mimic malignancy, in which cases, the clinical history can be the key to diagnosis. Vascular (sickle cell disease) and tumoral (aneurismal bone cyst, eosinophilic granuloma, metastases) lesions are relatively rare lesions but should be considered in the differential diagnosis, in the presence of certain imaging findings. The main difficulty is the differentiation between the benign and malignant nature; therefore, the main objective of this pictorial essay is to review the main skull lytic lesions found in pediatric age, describing the main findings in different imaging modalities (CT and MRI), allowing the neuroradiologist greater confidence in establishing the differential diagnosis, through a systematic and simple characterization of the lesions.

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.

Evaluation of Arachnoid Granulations in Cranial Dural Sinuses with Contrast-Enhanced 3-Dimensional T1-Weighted Magnetic Resonance Imaging

OBJECTIVE

Several studies in the literature have used contrast-enhanced magnetic resonance imaging to investigate arachnoid granulations protruding into the cranial dural sinuses. The current study aimed to investigate the protrusion of arachnoid granulations into the superior sagittal sinus, transverse sinus, straight sinus, and confluence of sinuses and determine the frequency of brain herniation into giant arachnoid granulations using contrast-enhanced 3-dimensional T1-weighted magnetic resonance imaging.

MATERIALS AND METHODS

Images of 550 patients with intra-sinus arachnoid granulations who underwent contrast-enhanced 3-dimensional T1-weighted thin-slice magnetic resonance imaging were retrospectively re-evaluated. Only 300 patients with at least 1 intra-sinus arachnoid granulation were included in the study. The protrusion of arachnoid granulations into superior sagittal sinus, transverse sinus, straight sinus, and confluence of sinuses was investigated. In addition, large arachnoid granulations and brain herniations into arachnoid granulations were also noted.

RESULTS

A total of 889 focal filling defects of arachnoid granulations, at least 1 in the dural sinus, were detected. Of the filling defects of arachnoid granulations, 183 were in the right transverse sinus, 222 in the left transverse sinus, 265 in superior sagittal sinus, 185 in straight sinus, and 34 in confluence of sinuses. Brain herniation into arachnoid granulations was detected in 8 (2.7%) of the patients included in the study. All the filling defects detected in the dural sinuses on post-contrast 3-dimensional T1-weighted images were isointense with cerebrospinal fluid and had round, oval, or lobulated contours. A positive weak correla- tion was found between patient age and the size and number of arachnoid granulations (r = 0.181, P < .01 and r=0.207, P < .001, respectively). It was observed that the size and number of arachnoid granulations increased as the age of the patients increased.

CONCLUSIONS

The distribution, shape, number, and size of intra-sinus arachnoid granulations can vary considerably. Brain herniation into arachnoid granulation can also be seen. Three-dimensional cranial magnetic resonance imaging sequences can be safely used in the evaluation of arachnoid granulations.

Dural Venous Sinus Arachnoid Granulations in Patients with Pulsatile Tinnitus

OBJECTIVE

To determine the relationship, if any, between dural venous sinus arachnoid granulations (AGs) and pulsatile tinnitus.

STUDY DESIGN

Retrospective case-control study.

METHODS

Between October 1999 and March 2020, magnetic resonance imaging of patients with tinnitus (pulsatile [PT] and nonpulsatile [NPT]) were assessed for the presence of dural venous sinuses AG. During the same interval, patients with AGs found incidentally on all magnetic resonance imagings ordered without an indication of tinnitus were reviewed. Demographic variables recorded included patient age, sex, race, body mass index, and a history of idiopathic intracranial hypertension (IIH) or obstructive sleep apnea. Location of AGs, when present, were recorded.

RESULTS

A total of 651 (PT 250, NPT 401) were found to have AGs. AGs had a higher prevalence in PT patients (10.4% [n = 26]) versus NPT patients (0.3% [n = 1]; odds ratio, 31.0; confidence interval 4.1-234; p < 0.001). Of the 77,607 patients who had an indication for imaging other than tinnitus, 230 patients (0.30%) were found to have incidental AGs, suggesting that the NPT cohort was an adequate control. Patients with PT were more likely to have a higher body mass index, be female, be non-White, and have an existing diagnosis of IIH. For all patients with AGs, AGs were more likely to be found in the lateral sinuses (i.e., sigmoid, transverse) in the PT group (odds ratio, 8.1; confidence interval, 1.1-61.1; p = 0.0218).

CONCLUSIONS

This study evaluates the association between AG and PT, finding higher rates of AG in patients with PT than in NPT. However, despite the increased prevalence of AG in patients with IIH, these data combined with existing literature would suggest that AGs are not necessarily the missing link to explain PT pathophysiology in IIH.

Molecular trans-dural efflux to skull bone marrow in humans with cerebrospinal fluid disorders

Dural sinuses were recently identified as a hub for peripheral immune surveillance of brain-derived antigens cleared through CSF. However, animal studies have also indicated that substances and cells may enter the intracranial compartment directly from bone marrow.

We used MRI and a CSF tracer to investigate in vivo whether intracranial molecules can move via dura to skull bone marrow in patients with suspicion of CSF disorders. Tracer enrichment in CSF, dural regions and within skull bone marrow was assessed up to 48 h after intrathecal administration of gadobutrol (0.5 ml, 1 mmol/ml) in 53 patients. In participants diagnosed with disease, tracer enrichment within diploe of skull bone marrow was demonstrated nearby the parasagittal dura, nearby extensions of parasagittal dura into diploe, and in diploe of skull bone remote from the dura extensions.

This crossing of meningeal and skull barriers suggests that bone marrow may contribute in brain immune surveillance also in humans.

The controversial entity of brain herniations into arachnoid granulations: A report of three cases with literature review

Brain herniation into arachnoid granulation (BHAG) is a quite recently described controversial entity in terms of both etiology and clinical significance. It comprises a herniation of brain tissue into a presumed preexisting arachnoid granulation in dural venous sinuses, calvarium, meningeal or diploic veins. Most often described as an incidental finding in patients examined for unrelated pathologies, some BHAGs can possibly be related to headache, epilepsy or conditions with increased intracranial pressure such as idiopathic intracranial hypertension (IIH) or pseudotumor cerebri (PTC). The number of reported cases is low and there are only three more recently published observational studies on this subject with results lacking statistical significance due to relatively few BHAGs analyzed. Therefore, BHAGs still need an increased focus from both the radiologists and clinicians and more published studies and cases are necessary to help in understanding their factual meaning, clinical and treatment implications. In this article we describe three new cases of BHAGs to the literature, with patients presenting with different symptoms.

A Pacchionian Puzzle

A 73-year-old male with a history of chronic ataxia presented with transient facial droop to the Emergency Department. A CT angiogram and MRI with diffusion weighted imaging (DWI) were negative for stroke. However, incidental note was made of numerous giant arachnoid granulation pits in the posterior fossa predominantly involving the left occipital bone (Figure 1). These arachnoid pits demonstrated multiple foci of herniation of the adjacent cerebellar parenchyma into the pits with gliosis of the herniated parenchyma and focal encephalomalacia of the subjacent cerebellar parenchyma. Review of bone windows on a remote CT brain performed almost 13 years earlier confirmed this to be a longstanding abnormality (Figure 2). The patient's physical exam was suggestive of cerebellar ataxia with left-sided dysmetria on finger to nose testing and a wide-based unsteady gait.

Tissue damage in herniated brain parenchyma into giant arachnoid granulations: demonstration with high resolution MRI

BACKGROUND

Brain herniation (BH) into arachnoid granulation has been remarkable in recent years.

PURPOSE

To evaluate the damage in herniated parenchyma into the giant arachnoid granulation (GAG) and to investigate the clinical-demographic importance of this damage.

MATERIAL AND METHODS

Patients with BH into GAG were retrospectively included in the study. Each of the patients had at least one high-resolution 3D magnetic resonance imaging (MRI) sequence. The arachnoid granulation dimensions, locations, and origin of herniated parenchyma were evaluated by two experienced radiologists. The demographic and symptomatic features of the patients were recorded from the hospital database.

RESULTS

A total of 27 patients (21 females, 6 males; age range 6-71 years; mean age 41.3 years) were found to contain BH into GAG. It was most commonly seen in the transverse sinus (67%); the origin was most common in the cerebellar parenchyma (56%). Abnormal signal and morphology were detected in herniated parenchyma in 11 (47%) patients, atrophy in six, and atrophy and gliosis in five. The most common complaints were headache (47%), while other frequent symptoms were vertigo (15%) and blurred vision (11%). There was a statistically significant positive correlation between frequency of damage in herniated brain parenchyma and the maximal size of GAG (P<0.05).

CONCLUSION

In patients with BH into GAG, parenchymal damage may be associated with various symptoms, such as headache and vertigo, although they have not been statistically proven. It is important to carefully evaluate hernia tissue, as the risk of tissue damage may increase in larger GAGs.

Cerebral Venous Thrombosis: Review of Diagnosis, Follow-Up, Late Complications and Potential Pitfalls

Cerebral venous thrombosis is a less common but relevant cause of stroke in adults. The clinical manifestations are nonspecific leading frequently diagnostic delays, so imaging findings are is of vital importance. Conventional imaging modalities, namely computed tomography and magnetic resonance imaging (MRI), allow identification of the thrombus and parenchymal involvement due to venous congestion to a variable degree, but this entity may appears as a nonexpected finding in a nonvenographic study. computed tomography and MRI venographies allow noninvasive confirmation of the diagnosis and adequate characterization of the extent of the thrombus and acute complications, both of them being robust diagnostic techniques. MR venography also can be done without the use of contrast media, which is especially important in certain clinical situations. Cerebral venous thrombosis needs follow-up, and imaging plays a key role in detection of late complications of the disease, including dural arteriovenous fistulas and intracranial hypertension due to veno-occlusive disease. Knowledge of other diseases and conditions that may mimic a thrombus is needed to avoid wrong diagnosis. In this article, we conduct a pictorial comprehensive review of cerebral venous thrombosis, including also the technical aspects of different imaging modalities, diagnosis and acute complications, follow-up, late complications and potential imaging mimics.

Cerebrospinal fluid tracer efflux to parasagittal dura in humans

The mechanisms behind molecular transport from cerebrospinal fluid to dural lymphatic vessels remain unknown. This study utilized magnetic resonance imaging along with cerebrospinal fluid tracer to visualize clearance pathways to human dural lymphatics in vivo. In 18 subjects with suspicion of various types of cerebrospinal fluid disorders, 3D T2-Fluid Attenuated Inversion Recovery, T1-black-blood, and T1 gradient echo acquisitions were obtained prior to intrathecal administration of the contrast agent gadobutrol (0.5 ml, 1 mmol/ml), serving as a cerebrospinal fluid tracer. Propagation of tracer was followed with T1 sequences at 3, 6, 24 and 48 h after the injection. The tracer escaped from cerebrospinal fluid into parasagittal dura along the superior sagittal sinus at areas nearby entry of cortical cerebral veins. The findings demonstrate that trans-arachnoid molecular passage does occur and suggest that parasagittal dura may serve as a bridging link between human brain and dural lymphatic vessels.

Mechanisms behind molecular transport from cerebrospinal fluid to dural lymphatic vessels remain unknown. This study demonstrates that trans-arachnoid molecular passage does occur and suggests that parasagittal dura may serve as a bridging link between human brain and dural lymphatic vessels.

An unusual vermiform giant arachnoid granulation

Arachnoid granulations are outpouchings of arachnoid membrane which extend into the dural sinuses or calvarium, surrounded by a capsule of dense connective tissue. Within dural sinuses, these appear as well-defined, nodular, rounded, or ovoid structures of focal localization. However, it is important to be aware of their variability in presentation in order to correctly identify them and distinguish them from other dural sinus pathology, especially a misdiagnosis of venous sinus thrombosis with risks of unnecessary anticoagulation, intravascular thrombolysis/thrombectomy, or invasive intracranial pressure monitoring. Here we demonstrate a case of a previously unreported giant intrasinus arachnoid granulation of an unusual vermiform morphology, unduly elongated up to 6 cm in length, involving a significant segment of the superior sagittal sinus. The proof of this diagnosis was the radiologic appearance on multiple modalities and an unchanged appearance over the long-term.

Giant arachnoid granulation in a child with benign intracranial hypertension: an unusual case

CASE PRESENTATION

A 6-year-old girl complained of diplopia and headache over a 2-week period after sustaining a minor head injury. Her neurological examinations were normal, but visual examination identified bilateral papilledema. Magnetic resonance imaging of the brain revealed a protruding nodular lesion causing compression within the anterior superior sagittal sinus in the midline, showing high signal intensity on T2-weighted imaging (T2WI) and low signal intensity on T1WI, similar to that of cerebrospinal fluid. Enhanced T1WI showed irregular narrowing of the anterior superior sagittal sinus adjacent to this lesion. The cortical vein drained to the frontal pole of the arachnoid granulation lesion and into the superior sagittal sinus. No other parenchymal abnormality was noted. A lumbar puncture showed increased opening pressure (30 mmHg), and the laboratory findings were normal. Based on the imaging and clinical findings, benign intracranial venous hypertension with giant arachnoid granulation was diagnosed. The patient's symptoms were reduced satisfactorily following daily treatment with 750 mg acetazolamide.

CONCLUSION

We report a case of giant arachnoid granulation involving the anterior superior sagittal sinus in a 6-year-old girl who presented with benign intracranial hypertension. Clinicians should be aware of this rare anatomic variant to avoid unnecessary invasive procedures or examinations in children with benign intracranial hypertension.

Arachnoid Granulations Mimicking Multiple Osteolytic Bone Lesions in the Occipital Bone

We report a rare case of arachnoid granulations mimicking multiple osteolytic bone lesions. A 66-year-old woman was admitted to a local clinic for a regular checkup. Upon admission, brain CT showed multiple osteolytic lesions in the occipital bone. These needed to be differentiated from multiple osteolytic bone tumor. Subsequent brain MRI revealed that the osteolytic lesions were isointense to cerebrospinal fluid, hyperintense on T2-weighted image, hypointense on T1-weighted image, and with subtle capsules around the osteolytic lesions that were visible after gadolinium injection. A bone scan revealed no radiotracer uptake. The lesions were in both the transverse sinuses and the torcular herophili. With typical radiological appearances of the lesions, the osteolytic lesions were diagnosed as multiple arachnoid granulations. No further treatment was planned. A 1-year follow-up brain CT scan revealed no change. We should consider the possibility of arachnoid granulations when multiple osteolytic lesions are observed in the occipital bone.

Spectrum of lytic lesions of the skull: a pictorial essay

Abstract

Lytic lesions of the skull include a wide range of diseases, ranging from benign conditions such as arachnoid granulations or vascular lacunae, to aggressive malignant lesions such as lymphomas or metastases. An early and correct characterisation of the nature of the lesion is, therefore, crucial, in order to achieve a fast and appropriate treatment option. In this review, we present the radiological appearance of the most frequent lytic lesions of the skull, describing findings from different imaging modalities (plain X-rays, CT and MRI), with particular attention to diagnostic clues and differential diagnoses.

Teaching Points

• Osteolytic skull lesions may be challenging to diagnose.

• Association of different imaging techniques may aid image interpretation.

• Clinical information and extensive knowledge of possible differential diagnoses is essential.

• Some osteolytic tumours, although benign, may present as locally aggressive lesions.

• Malignant lesions require accurate staging, followed by variable treatment approaches.

Giant Posterior Temporal Bone Arachnoid Granulations: CT and MRI Findings

OBJECTIVE

The radiologic appearance of arachnoid granulations (AGs) in typical locations is well established and they are rarely mistaken for other pathologies. However, when large and seen in atypical locations, such as along the posterior petrous bone, AGs can be a source of diagnostic and therapeutic confusion. We present two cases of giant posterior temporal bone AGs and review their clinical presentation, potential complications, and an imaging-based differential diagnosis.

PATIENTS

Two patients with surgically or pathologically proven giant symptomatic AGs in the posterior petrous bone.

MAIN OUTCOME MEASURE

Clinical presentation, radiological features, surgical findings, and potential complications of giant AGs.

RESULTS

In two middle-aged women (37 and 55 years), computed tomography (CT) demonstrated solitary large lytic lesions in the posterior right petrous temporal bone. These were similar in appearance to cerebrospinal fluid (CSF) on magnetic resonance imaging (MRI), though they exhibited some minor deviations such as thin internal septations, mild peripheral enhancement, and heterogeneous signal on fluid-attenuated inversion recovery (FLAIR). The MRI appearance effectively distinguished the giant AGs from other lesions that can occur in this area such as endolymphatic sac tumor (ELST). Surgery was successfully performed to prevent complications from a CSF leak.

CONCLUSION

The posterior temporal bone is an atypical location for AGs and can lead to diagnostic confusion, particularly when they are large. Familiarity with the characteristic imaging appearance of giant AGs in this location can help avoid misinterpretation as a more aggressive pathology and help recognize patients who are at risk for a CSF leak.

Normal neuroanatomical variants that may be misinterpreted as disease entities

Variations of normal development and benign incidental anomalies are frequently observed on diagnostic neuroimaging. It is important these are recognised for what they are, as misinterpretation may result in unnecessary further investigation, follow-up imaging and anxiety. In this article, we review benign intracranial anomalies commonly referred to our unit for specialist neuroradiology advice or multidisciplinary discussion, concerning cysts of the pineal gland and pituitary fossa, vascular anomalies, and perivascular spaces. This article outlines the embryology and development, the various imaging features as well as the clinical relevance and differential diagnoses of each normal neuroanatomical variant.

Brain Herniation into Giant Arachnoid Granulation: An Unusual Case

Arachnoid granulations are structures filled with cerebrospinal fluid (CSF) that extend into the venous sinuses through openings in the dura mater and allow the drainage of CSF from subarachnoid space into venous system. Usually they are asymptomatic but can be symptomatic when large enough to cause sinus occlusion. We report a rare case of a brain herniation into a giant arachnoid granulation in an asymptomatic elderly male patient, which was discovered incidentally.

Giant Arachnoid Granulation Associated with Anomalous Draining Vein: A Case Report

Giant arachnoid granulations (AG) can mimic intracranial lesions. Knowledge of these structures can help avoid misdiagnosis when interpreting imaging. Here, we report a child who presented with a mass within the superior sagittal sinus and an anomalous draining vein. Herein, the diagnosis of a giant AG was made. Clinicians who view or interpret imaging of the head should be aware of these anatomical variants and though when very large, apparently, do not necessarily result in pathology. Based on our case report, giant AG might also demonstrate anomalous draining veins.

Giant arachnoid granulations mimicking pathology. A report of three cases

We describe three cases of incidentally found lesions in the dural venous sinuses on magnetic resonance imaging, that other had erroneously considered pathological entities. We made the diagnosis of giant arachnoid granulations. The differential diagnosis with thrombosis or intrasinusal tumoral lesions was easily made on the basis of three typical radiological features of the granulations: the hyperintensity of the lesions on FLAIR, a blood vessel within the lesion and bone erosion.

'Do not touch' lesions of the skull base

Imaging of the skull base presents many challenges due to its anatomical complexity, numerous normal variants and lack of familiarity to many radiologists. As the skull base is a region which is not amenable to physical examination and as lesions of the skull base are generally difficult to biopsy and even more difficult to operate on, the radiologist plays a major role in directing patient management via accurate image interpretation. Knowledge of the skull base should not be limited to neuroradiologists and head and neck radiologists, however, as the central skull base is routinely included in the field of view when imaging the brain, cervical spine, or head and neck with computed tomography or magnetic resonance imaging, and hence, its nuances should be familiar to general radiologists as well. We herein review the imaging findings of a subcategory of lesions of the central skull base, the 'do not touch' lesions.

Cranial arachnoid protrusions and contiguous diploic veins in CSF drainage

BACKGROUND AND PURPOSE

Studies have suggested that arachnoid villi or granulations found in the walls of the cranial dural sinuses, olfactory mucosa, and cranial nerve sheaths function as outlets for intracranial CSF. However, their role as CSF outlets has not yet been verified. Here we show that arachnoid protrusions and contiguous diploic veins provide an alternative drainage route for intracranial CSF.

MATERIALS AND METHODS

Four hundred patients with intact skull, dura mater, and dural sinuses underwent MR imaging to explore arachnoids protruding into the skull and diploic veins. Patients with symptoms of increased intracranial pressure or intracranial hypotension were excluded. For 15 patients undergoing craniotomy, both peripheral and diploic venous blood was collected. Albumin and the CSF-specific biomarkers were measured by enzyme-linked immunosorbent assay.

RESULTS

With MR imaging, arachnoid protrusions into the skull and contiguous diploic veins were consistently identified throughout the cranium with their characteristic appearance depending on the cranial region. In addition, elevated amounts of prostaglandin D synthase and cystatin C were confirmed in diploic veins compared with peripheral venous blood.

CONCLUSIONS

Diploic veins are distributed ubiquitously throughout the cranium. A portion of the intracranial CSF may be drained through arachnoid protrusions and contiguous diploic veins.

Dural sinus filling defect: intrasigmoid encephalocele

Filling defects of dural venous sinuses are considered to be a challenging problem especially in case of symptomatic patients. Many lesions have to be ruled out such as sinus thrombosis, arachnoid granulations and tumours. Encephalocele into dural sinus is also a rare cause of these filling defects of dural sinuses. Here, we report an extremely rare case with spontaneous occult invagination of temporal brain tissue into the left sigmoid sinus and accompanying cerebellar ectopia.

Multiple occipital defects caused by arachnoid granulations: Emphasis on T2 mapping

A 56-year-old man presented with a 6-mo history of headache. Although neurological and laboratory examinations were normal, computed tomography (CT) scan was performed which revealed multiple occipital osteolytic lesions, which were suspected to be multiple myeloma. Subsequently nuclear magnetic resonance imaging (MRI) showed that these lesions presented with a cerebrospinal fluid (CSF)-like signal intensity, no diffusional restriction and intrinsic mass-like enhancement on conventional sequences were seen. T2 relaxation time was similar to that of CSF in the ventricles and adjacent subarachnoid space on T2-mapping. Single photon emission CT with ^99mTc-Methyl diphosphonate was performed which revealed no increased radiotracing accumulation. Finally, these lesions were diagnosed as mutiple arachnoid granulations (AGs). The headache was treated symptomatically with medical therapy. On follow up examination after 6 mo no evidence of tumor was detected. This report aimed to illustrate the appearance and differentiation of occipital defects caused by multiple AGs on CT and MRI, with emphasis on the findings from T2 mapping.