Giant Arachnoid Granulations Mimicking Pathology

Abstract

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.

Ectopic arachnoid granulation involving a rare intracranial venous sinus variant

“…The prevalence and size of these structures increases with age in response to increased CSF pressure and volume from the subarachnoid space [3,4,9]. Historically, it has been postulated that the number and size of AG is an indication of CSF pressure [5]; however, recent research indicates that when CSF pressure is elevated, they are only secondarily involved in CSF absorption [5].…”

“…The superior longitudinal sinus, cavernous sinus, superior petrosal sinus, middle meningeal vein, sphenoparietal and straight sinuses, are regions in which AG have been identified and documented [5,6]. The features and various locations in which AG are found has led many investigators to include dural sinus thrombosis, meningioma, arachnoid cysts and many others in the broad differential for AG [4,6,9]. While initially described by Pacchioni over 300 years ago, AG are still poorly described, especially those residing in the middle cranial fossa [1].…”

“…Pacchionian bodies or arachnoid granulations (AG) are cerebrospinal fluid filled protrusions from the arachnoid mater that extend from the subarachnoid space through apertures in the dura mater into the venous system [3,4]. First described in 1705 and named after the Italian anatomist Antonio Pacchioni [4], these cerebrospinal fluid (CSF)-filled meningothelial-lined protrusions are distended arachnoid villi (AV) that function in filtration and reabsorption of CSF into the venous circulation [3,4,9].…”

“…First described in 1705 and named after the Italian anatomist Antonio Pacchioni [4], these cerebrospinal fluid (CSF)-filled meningothelial-lined protrusions are distended arachnoid villi (AV) that function in filtration and reabsorption of CSF into the venous circulation [3,4,9]. Arachnoid villi are microscopic structures that when hypertrophied through increasing CSF volume and pressure, become arachnoid granulations, typically ranging in size from 2 to 8 mm allowing them to be viewed grossly [9].…”

“…Arachnoid villi are microscopic structures that when hypertrophied through increasing CSF volume and pressure, become arachnoid granulations, typically ranging in size from 2 to 8 mm allowing them to be viewed grossly [9]. While there is no consensus in the literature, arachnoid granulations that are greater than 1 cm or those large enough to fill the lumen of a dural venous sinus leading to local dilatation and filling defects are termed giant AG [3,4]. These extensions of the arachnoid can grow to expand the inner table of the skull, most commonly around the midline in the posterior frontal or anterior parietal area [3].…”