Brain Herniation into Arachnoid Granulations an Uncommon Entity

Brain Herniation into Arachnoid Granulations: an Uncommon Entity with Variable Clinical and Radiographic Manifestations Greta B. Liebo, MD, Vance T. Lehman, MD, Laurence J. Eckel, MD, Kara M. Schwartz, MD, John (Jack) I. Lane, MD. Department of Neuroradiology, Mayo Clinic-Rochester. ASNR, 2015 Annual Meeting, Chicago, IL, April 25 -30. Control #965 e. Ed. E-141

Disclosures No disclosures

Background • Arachnoid granulations (AG) are normal structures, created by invaginations of the arachnoid membrane that extend through gaps in the dura, protruding into the dural venous sinuses and occasionally the bone. 1 -13 • Rare cases of “encephaloceles, ” or herniation/ invagination of brain parenchyma into these AGs have been reported, but there are very few reports and little analysis of this in the current literature. 4 -12 • Our series of 10 patients is the largest case series to date.

Purpose To characterize the variable radiographic appearance and clinical significance of brain herniation into AGs

Approach/Methods • Retrospective imaging and clinical chart review from our collective clinical experience

Approach/Methods • Patient demographics, location of the AGs, and the location of herniated parenchyma were characterized • The clinical presentations were reviewed • The presence/absence of evidence of elevated intracranial pressure at presentation was recorded • Associated MR signal change and adjacent encephalomalacia were also documented

Approach/Methods • Brain herniations into AG were categorized into 3 broad clinical categories: 1) Incidental: No correlation of imaging findings with clinical history 2) Indeterminate: Possible related clinical symptoms 3) Likely Symptomatic : Clinical symptoms present that seem to be related to AG with brain herniation

CASE REPORTS:

Clinical Categories • Incidental: • Indeterminate: • Likely symptomatic: # of Cases 6 1 3 • Secondary to effects of the AG itself: • Secondary to presumed incarceration: (2) (1)

INCIDENTAL CASES

CASE 1: A 5 year old female with past medical history significant for viral meningitis in infancy presented for work up of newly diagnosed absence epilepsy. Electroencephalogram (EEG) demonstrated left frontal predominant interictal epileptiform discharges , raising additional concern for a more focal process with complex partial or secondary generalization of seizure activity. A B MRI was performed at the time of initial seizure workup. Coronal FIESTA (a), axial FIESTA (b), coronal MPRAGE (c), and coronal postcontrast T 1 (d) demonstrate an AG in the left transverse sinus containing a small invagination of parenchyma from he posteroinferior temporal lobe ( ). The neurologists did not believe the herniation of temporal lobe was contributory to the patient’s seizures. C D

CASE 2: A 70 year old female with history of nephrectomy for renal cell carcinoma presented with multifocal foot paresthesias involving the right and left feet, forearms, hands, and right cheek. MRI was ordered to evaluate for a central etiology. Axial T 2 (a, b), axial postcontrast T 1 (c), and coronal postcontrast T 1 (d) demonstrate herniation of the left cerebellar hemisphere into the transverse sinus ( ). No specific abnormality was identified to account for the patient’s symptoms. A B C D

A CASE 3: A 60 year old male experienced an indeterminate episode of neurologic dysfunction characterized by right upper extremity monoparesis. He was in the hospital at the time, recovering from an orthopedic knee procedure complicated by lower extremity deep venous thrombosis. B CT and follow up MRI were ordered to evaluate for TIA or stroke. Axial bone kernel CT (a), axial T 2 (b), coronal postcontrast T 1 (c), and sagittal postcontrast T 1 (d) demonstrate cystic irregularity with remodeling of the left occipital bone ( ), a classic appearance for an AG. Herniation of the left cerebellum into the AG is seen, isointense to brain on all sequences ( ). C D

A B C CASE 4: A 62 year old male presents for follow up status post radiation and chemotherapy for a resected right frontal anaplastic oligodendroglioma. His postoperative course was complicated by hemorrhage and intracranial hypertension. Axial T 2 CISS (a-c) and sagittal postcontrast T 1 SPACE (d) images demonstrate multiple tiny AGs eroding into the occipital bones, containing small invaginations of cerebellar parenchyma ( ). D

July 2011, Ax T 2 March 2013, Ax FLAIR Nov 2013, Ax T 2 CASE 5: A 65 year old female presented with 3 year history of progressive slurring and gait imbalance, now requiring the use of a wheelchair. On exam, she was ataxic and dysarthric, with left greater than right spastic hemiparesis and tremors. Oct 2014, Ax T 2 Review of outside her MRIs dating back to 2011 demonstrated progressive pontine and cerebellar atrophy with increased signal in the pontine white matter tracts suggestive of multiple system atrophy. Additionally, a prominent AG into the transverse sinus was observed ( ), with focal fibrotic appearing bands extending to the left cerebellar hemisphere, and focal cerebellar encephalomalacia immediately subjacent to the granulation ( ).

CASE 6: A 53 year old asymptomatic male with history of metastatic colorectal carcinoma presented for restaging brain MRI. Axial T 2 (a), coronal CISS (b), axial FLAIR (c), and sagittal postcontrast T 1 (d) demonstrate a cystic abnormality with remodeling of the right occipital bone, typical in appearance for an AG ( ). Herniation of the right cerebellar hemisphere and multiple septations are seen within the AG. There is focal encephalomalacia in the cerebellum, immediately subjacent to the herniation ( ). A C B D

INDETERMINATE CASES

CASE 7: A 20 year old female without significant past medical history presented with 8 months of incapacitating, medically refractory headaches. She described her pain as typically right or left temporal, but infrequently posterior. She also reported more recent “pressure-type sensation” that lasts only a few seconds over her occiput. A B Noncontrast head CT (a) demonstrates a complex predominantly CSF density filling defect in the torcula. Axial T 2 (b), sagittal pre-contrast T 1 (c), and sagittal post-contrast T 1 (d) demonstrate herniation of the left cerebellar hemisphere into a giant AG ( ). C D

LIKELY SYMPTOMATIC CASES

A B C CASE 8: A 70 year old woman presented history of recurrent fluid in the left ear, status post tympanostomy tube placement, with persistent clear left ear drainage and positive beta-2 transferrin test. Axial bone kernal CT (a) demonstrates erosion of the posterior petrous plate ( ) and mastoid effusion. Axial T 2 (b) and postcontrast T 1 (c) images show herniation of the left cerebellum through the bone defect ( ). During left middle fossa craniotomy, the dura was described as very thin, but intact, without obvious defect leading into the mastoid or middle ear space. On mastoidectomy, a fairly large meningoencephalocele was identified as the obvious source of CSF leak. Note: While no discrete cystic mass is identified, AGs have long been suspected to be responsible for erosions in this location. 6, 11 -13 This theory is also supported by the focal erosive appearance of the abnormality on CT. 13

A C B D Figure: Preoperative Coronal CT of the right (a) and left (b) temporal bones, axial CT of the right temporal bone (C), and Axial T 2 SPACE of the right IAC (d). E Figure: Postoperative axial post-contrast T 1 (e) and T 2 SPACE (f). F CASE 9: A 56 year old female without significant past medical history presented with a 3 year history of progressive right-sided hearing loss with tinnitus and recurrent vertigo. Repeat brain MRIs over a 10 month period showed a stable, multiloculated extra-axial cystic nonenhancing mass within the lateral aspect of the right cerebellopontine cistern ( ). It was associated with extension through the posterior cortex of the right temporal bone. The lesion was isointense to CSF without restricted diffusion and CT scan confirmed bony erosion ( ). A right suboccipital craniotomy was performed and the radiographic bony defect was immediately appreciated within the cerebellopontine angle. The defect was superficial and inferior to the internal auditory canal with a small vascular bundle extending from the cerebellum into the bony defect, tethered by the dura. The lesion had the gross appearance of thickened arachnoid membrane resembling and arachnoid cyst. Pathology confirmed a benign process comprised of several components including arachnoid cells, fibrous tissue, portions of bone, and neuroglial tissue. At 3 month follow-up, MRI showed complete resection and continued right sided hearing loss. Focal encephalomalacia of the cerebellum was observed, immediately adjacent to the abnormality, both before and after resection, suggestive of prior strangulation and infarction ( ).

A C B D CASE 10: A 46 year old woman presented with 10 days of headache, which rapidly progressed from mild to “excruciating, stiff neck, and new onset diplopia. A Head CT was ordered in the ED, but showed no acute abnormality. She stayed in bed for 2 more weeks, with persistent headache, diplopia, and fatigue, before returning for follow up with a neurologist. A brain MRI was ordered, but symptoms resolved spontaneously prior to her MRI appointment. The initial screening head CT (a, b) demonstrates large erosions of the occipital bone ( ), typical in appearance for AGs. Ax FLAIR (c), Axial T 2 (d), sagittal FLAIR (e), and sagittal postcontrast T 1 (f) images demonstrate protrusion of the cerebellar hemispheres into the AGs ( ) with adjacent edema ( ) and enhancement ( ) the medial right cerebellar hemisphere. Initial differential considerations included tumor, infection, inflammation, or vascular etiology. However, there was no leptomeningeal enhancement or other abnormality to account for the cerebellar findings. Over the course of the next 3 months, the cerebellar signal abnormality resolved, suggestive of prior incarceration without strangulation/infarction. E F

Discussion • Background & Literature Review: – One of the major difficulties in reviewing the literature regarding this topic is the inconsistency of language and description across different case reports. • Some authors prefer the term invagination 5 over brain herniation 7, 10, 11, perhaps trying to emphasize the assumed benignity of this entity. • Others designate the abnormality as an encephalocele 8, 9, 12 or meningoencephalocele 6, particularly if it occurs in the temporal bone, along the posterior petrous face. – These inconsistencies highlight the variability in patient presentation and outcome.

Discussion • Proposed Pathophysiology: – Most authors believe that brain herniation into AGs occurs spontaneously 8 -10 – Some authors have suggested that increased intracranial pressure may be a predisposing factor. 7, 8, 10, 12 – In our experience: • None of the patients in our series had signs or symptoms of increased intracranial hypertension at the time of exam. – Only 1 patient (case 4) had history of prior intracranial hypertension, but the imaging appearance of the AGs was unchanged from earlier examinations suggesting that herniation preceded the period of intracranial hypertension. • However, we noticed a marked propensity of herniations into AGs occur in the posterior fossa, involving the distal transverse sinuses, posterior petrous ridges, or occipital bones.

Discussion • Proposed Pathophysiology: – Most authors believe that brain herniation into AGs occurs spontaneously 8 -10 Based on our experience, we – Some authors have suggested that increased intracranial pressure may be a predisposing factor. 7, 8, 10, 12 favor that herniation occurs – In our experience: spontaneously, primarily – Only 1 patient (case 4) had history of prior intracranial hypertension, but dependent on the location of the imaging appearance was unchanged from earlier examinations suggesting that herniation preceded the period of intracranial hypertension. arachnoid granulation. • However, we noticed a marked propensity of herniations into AGs • None of the patients in our series had signs or symptoms of increased intracranial hypertension at the time of exam. occur in the posterior fossa, involving the distal transverse sinuses, posterior petrous ridges, or occipital bones.

Discussion • Epidemiology: Our overall experience – Age: 5 -70 years; mean: 50 year. – Sex: 7 female, 3 male

Discussion • Epidemiology: Our overall experience – Age: 5 -70 years; mean: 50 year. Prevalence appears to increase – Sex: 7 female, 3 male with age, correlating with concurrent increase in size and number of AGs.

Discussion • Clinical Associations: – Headaches, tinnitus, and rarely intracranial venous hypertension have all been reported with giant AGs WITHOUT BRAIN HERNIATION, though no direct correlation has been established. 1, 6, 7, 10

Discussion • Clinical Associations: Our overall experience – 60% Incidental (unrelated to clinical symptoms) – 10% Indeterminate – 30% Associated directly with clinical symptoms and/or evidence of incarceration/strangulation

Discussion • Clinical Associations: By Location Cases Incidental Distal Transverse Sinus Case 1 x Case 2 x Case 5 x Torcula Case 7 Posterior Petrous Face Case 8 x Case 9 x Occipital Bones Symptomatic x Case 3 x Case 4 x Case 6 x Case 10 Indeterminate x

Discussion • Clinical Associations: By Location Brain herniation into AGs along the posterior petrous plate seem to have the highest rate of symptomatic presentation. • Symptoms are likely related to associated bony remodeling, dehiscence, and subsequent mastoid/middle ear effusion or CSF leak rather than the brain herniation itself. • The presence of brain herniation in this location may be symptomatically inconsequential, though important to document, as it may aid in presurgical planning, altering the surgical approach.

Discussion • Clinical Associations: Strangulation and Infarction • Our experience: – 30% of cases (3/10) were discovered incidentally, with subjacent encephalomalacia suggestive of old strangulation and infarction. – 10% of cases (1/10) had radiographic signs and symptoms suggestive of acute ischemia from incarceration without complete infarction. • This association has not been previously reported to our knowledge.

Discussion • Clinical Associations: Strangulation and Infarction • Our experience: – 30% of cases (3/10) were discovered incidentally, with subjacent This suggests there is a propensity for the herniated encephalomalacia suggestive of old strangulation and infarction. brain tissue to strangulate and infarct. – 10% of cases (1/10) had radiographic signs and symptoms suggestive of acute ischemia from incarceration without complete infarction. • This association has not been previously reported to our knowledge.

Discussion • Clinical Associations: Strangulation and Infarction • Our experience: – 30% of cases (3/10) were discovered incidentally, with subjacent This suggests there is a propensity for the herniated encephalomalacia suggestive of old strangulation and infarction. brain tissue to strangulate and infarct. – 10% of cases (1/10) had radiographic signs and symptoms suggestive of acute ischemia from incarceration without complete The lack of relevant patient history in these cases infarction. suggests that many of these infarctions were “silent” • This association has not been previously reported to our or subclinical, perhaps presenting only with knowledge. headache or no symptoms at all.

Discussion • Clinical Implications: – We expect detection of brain herniation into AGs to increase over time, owing to improved MR imaging techniques and spatial resolution. – The propensity for incarceration or strangulation raises the question of necessary follow up or management. • If discovered incidentally, no further follow up may be indicated, particularly because the majority of strangulation/infarction events are subclinical. • If symptomatic at presentation, there may be a role for follow up imaging or elective surgical decompression. – Recommended imaging sequences: FIESTA or CISS with multiplanar reconstructions. – However, larger population-based and prospective case studies are necessary to fully understand the prevalence, natural history, and clinical implications of this entity. – In the meantime, the focus should be on recognition and education, particularly in cases undergoing pre-operative evaluation for related or unrelated surgical planning.

Conclusion • Brain herniation into AGs is a rare finding with variable clinical and radiographic manifestations. • While the pathophysiology is not well understood, we favor that herniation occurs spontaneously, with incidence related primarily to the location of the AG. • While most cases are thought to be asymptomatic, patients may present with a variety of symptoms related to bony remodeling of the temporal bone or parenchymal incarceration/strangulation.

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