KEY FACTS Terminology Definition: Nonspecific, nonneoplastic benign inflammatory lesion without identifiable local or systemic causes characterized by polymorphous lymphoplasmacytic infiltrate Idiopathic orbital inflammation May involve any part(s) of orbit Idiopathic extraorbital inflammation Intracranial involvement : Spread through superior orbital fissure (SOF) or optic canal (OC) – Cavernous sinus, dura, Meckel cave Skull base-extracranial involvement : Spreads from inferior orbital fissure (IOF) or through orbital wall –…

KEY FACTS Imaging Best clue Anterior or central skull base ( SB ) defect on bone CT with positive β2-transferrin test on nasal secretions Anterior SB bone CT findings Bone defect in cribriform plate, lateral lamella of middle turbinate or ethmoid roof Other evidence for fracture, functional endoscopic sinus surgery (FESS), congenital cephalocele Central SB bone CT findings Bone defect in sella floor (transnasal pituitary surgery,…

KEY FACTS Terminology Headache caused by ↓ intracranial CSF pressure Imaging Classic imaging Diffuse dural thickening/enhancement – Smooth, not nodular or “lumpy-bumpy” Downward displacement of brain through incisura (“slumping” midbrain) Veins, dural sinuses distended ± subdural hygromas/hematomas Other: Midbrain elongated, ambient cisterns effaced on axial T2WI Top Differential Diagnoses Meningitis Meningeal metastases Chronic subdural hematoma Dural sinus thrombosis Postsurgical dural thickening Idiopathic hypertrophic cranial pachymeningitis Clinical…

Overview Understanding the anatomy of the skull, scalp, and meninges is key to formulating a correct imaging diagnosis. Several important differential diagnoses are based on location. However, each of these locations requires a different imaging approach. For example, CT is often the best imaging modality for lesions of the skull and scalp. When faced with a complex skull base lesion, a combination of bone CT and…

KEY FACTS Terminology Definition: Cerebellopontine angle-internal auditory canal (CPA-IAC) metastases refers to systemic or CNS neoplasia affecting area of CPA-IAC Imaging 4 major sites: Leptomeningeal (pia-arachnoid), dura, flocculus, and choroid plexus T1WI C+ MR Leptomeningeal metastases : Diffuse thickening and enhancement of cranial nerves in IAC Dural metastases : Thickened enhancing dura; may be diffuse or focal Floccular metastases : Enhancing floccular mass extends into CPA…

KEY FACTS Terminology Definition: Benign, unencapsulated neoplasm arising from meningothelial arachnoid cells of CPA-IAC dura Imaging 10% occur in posterior fossa When in CPA, asymmetric to IAC porus acusticus NECT Variable; often hyperdense – 25% calcified; 2 types seen □ Homogeneous, sand-like (psammomatous) □ Focal “sunburst,” globular, or rim pattern Bone CT: Hyperostotic or permeative-sclerotic bone changes possible (en plaque type) T2WI MR: Pial blood vessels…

KEY FACTS Terminology Benign encapsulated nerve sheath tumor composed of differentiated neoplastic Schwann cells 99% of all schwannomas associated with cranial nerves 95% involve CN8 < 1% of all intracranial schwannomas are intraparenchymal Imaging CT Iso- to slightly hyperdense compared with brain Adjacent bone, foramina may show smooth, scalloped enlargement Avid, sometimes heterogeneous enhancement MR Heterogeneously hyperintense on T2WI, FLAIR 100% enhance (avid, heterogeneously) Peritumoral arachnoid…

KEY FACTS Terminology Vestibular (“acoustic”) schwannoma (VS): Benign tumor from Schwann cells that wrap vestibular CN8 branches in cerebellopontine angle-internal auditory canal (CPA-IAC) Imaging T1WI fat-saturated enhanced MR = gold standard Focal, enhancing mass of CPA-IAC cistern centered on porus acusticus Small VS: Ovoid-enhancing intracanalicular mass Large VS: “Ice cream on cone” shape in CPA and IAC 15% with intramural cysts (low signal foci) 0.5% with…

KEY FACTS Terminology Definition: Vascular loop compressing facial nerve at its root exit zone within cerebellopontine angle (CPA) cistern causing hemifacial spasm Imaging High-resolution T2WI MR or source MRA images show serpentine asymmetric signal void (vessel) in medial CPA Anterior inferior cerebellar artery (50%) > posterior inferior cerebellar artery (30%) > vertebral artery (15%) > vein (5%) Top Differential Diagnoses Aneurysm, CPA-IAC Arteriovenous malformation, CPA Developmental…

KEY FACTS Terminology Trigeminal neuralgia (TN) definition: Vascular loop compressing trigeminal nerve (CN5) at its root entry zone (REZ) or preganglionic segment (PGS) Imaging High-resolution MR: Serpiginous asymmetric signal void (vessel) in cerebellopontine angle (CPA) CN5 REZ or PGS CN5 PGS atrophy: Severe, prolonged compression Compressing vessel will bow PGS Offending vessels: Superior cerebellar artery (55%) > AICA (10%) > basal artery (5%) > variant vein…

KEY FACTS Terminology Bell's palsy (BP): Herpetic peripheral facial nerve paralysis secondary to herpes simplex virus Imaging T1WI C+ fat-saturated MR: Fundal “tuft” and labyrinthine segment CN7 show intense asymmetric enhancement Entire intratemporal CN7 may enhance Imaging note: Classic rapid-onset BP requires no imaging in initial stages If atypical Bell's palsy , search with imaging for underlying lesion Top Differential Diagnoses Normal enhancement of intratemporal CN7…

KEY FACTS Terminology Arachnoid cyst (AC): Developmental arachnoid duplication anomaly creating cerebrospinal fluid (CSF)-filled sac Imaging Sharply demarcated ovoid extraaxial cisternal cyst with imperceptible walls with CSF density (CT) or intensity (MR) AC signal parallels (is isointense to) CSF on all MR sequences Complete fluid attenuation on FLAIR MR No diffusion restriction on DWI MR Top Differential Diagnoses Epidermoid cyst in cerebellopontine angle (CPA) Cystic vestibular…

KEY FACTS Terminology Definition: Congenital inclusion of ectodermal epithelial elements during neural tube closure Imaging CPA cisternal insinuating mass with high signal on DWI MR 90% intradural, 10% extradural; margins usually scalloped or irregular; cauliflower-like margins with “fronds” possible TI and T2: Isointense or slightly hyperintense to cerebrospinal fluid DWI: Restricted diffusion makes diagnosis Top Differential Diagnoses Arachnoid cyst in CPA Cystic neoplasm in CPA Cystic…

Terminology The contents of the cerebellopontine angle (CPA) and internal auditory canal (IAC) cisterns include the facial nerve (CN7), the vestibulocochlear nerve (CN8), and the anterior inferior cerebellar artery (AICA) loop. The bony IAC, its fundal crests (vertical and horizontal), and its opening in the porus acusticus are also included as part of this discussion. Embryology The temporal bone forms as 3 distinct embryological events: (1)…

KEY FACTS Terminology Lymphocytic hypophysitis (LH) Synonyms: Adenohypophysitis, primary hypophysitis, stalkitis Idiopathic inflammation of pituitary gland &/or stalk Imaging Thick stalk (> 2 mm + loss of normal “top to bottom” tapering) ± enlarged pituitary gland 75% show loss of posterior pituitary “bright spot” Enhances intensely, uniformly May have adjacent dural or sphenoid sinus mucosal thickening Top Differential Diagnoses Macroadenoma Pituitary hyperplasia Adolescent pituitary gland Granulomatous…

KEY FACTS Terminology Upper limit of normal pituitary height varies with age, sex Pregnant/lactating female patients: 12 mm Young menstruating female patients: 10 mm Male patients, postmenopausal women: 8 mm Infants, children: 6 mm Nonphysiologic hyperplasia seen with Hypothyroidism, Addison disease, or other end-organ failure Some neuroendocrine neoplasms Imaging Enlarged homogeneously enhancing pituitary gland with convex superior margin Best technique: High-resolution MR Sagittal/coronal T1; coronal T2…