Susac syndrome

Findings

Figure 1 and Figure 2: FLAIR images reveal multiple punctate T2 signal hyperintensities in the cortical, subcortical white matter and bilateral centrum semiovale.
Figure 3: Coronal T2 weighted image demonstrates a focus of abnormal T2 signal in the of the corpus callosum (yellow arrow).
Figure 4: Axial T1 post contrast image demonstrates punctuate enhancement of lesions within the centrum semiovale.

Differential diagnosis
- Susac syndrome
- Multiple sclerosis (MS)
- Acute disseminated encephalomyelitis (ADEM)
- Transient ischemic attacks
- Systemic vasculitis
- Thrombophilic disorders
- Mitochondrial encephalopathy


Diagnosis: Susac syndrome


Susac syndrome is a rare microangiopathy characterized by a clinical triad of encephalopathy, branch retinal artery occlusions, and hearing loss. The syndrome predominantly affects women in their third and fourth decades of life, between the ages 18 and 42. Though the exact pathogenesis of this disorder is unknown, the findings of retinal microangiopathy and brain biopsies suggest a small vessel vasculitis leading to arteriolar occlusion and microinfarction of cerebral, retinal and cochlear tissue.

If a patient with a history of acute encephalopathy also develops hearing loss or acute visual loss, Susac syndrome should be considered.

The neuroimaging study of choice is the MRI, which typically demonstrates a pattern of punctuate, multifocal supratentorial lesions. The disease invariably involves the corpus callosum and affects both white and grey matter. Leptomeningeal enhancement may occur.

Multiple sclerosis (MS) and acute disseminated encephalomyelitis (ADEM) can mimic the MRI changes seen in patients with Susac syndrome. However, the callosal lesions in Susac syndrome are centrally located while patients with MS and ADEM typically have lesions involving the undersurface of the corpus callosum. Deep gray matter involvement commonly occurs in ADEM but is very rare in MS. Leptomemingeal involvement is not typical of either MS or ADEM. Demyelination is not a typical feature of Susac syndrome.

Treatment currently consists of intravenous methylprednisolone, followed by oral steroids in conjunction with the use of intravenous immunoglobulin (IVIG). The condition is typically self limiting, but can take up to five years to resolve.

Vestibular schwannoma (with communicating hydrocephalus)

Differential diagnosis:
- Vestibular schwannoma
- Meningioma
- Epidermoid cyst
- Facial nerve schwannoma
- Arachniod cyst


Differential overview

Meningioma is the second most common CPA mass and may mimic a vestibular schwannoma. They are benign, unencapsulated neoplasm arising from meningothelial arachnoid cells of CPA-IAC dura. On CT, meningiomas will appear as a calcified dural based mass eccentric to the IAC with a positive meningeal sign, i.e. enhancement of the meningeal tail. 90% will have strong, uniform enhancement on contrasted CT studies. Vestibular schwannomas will not calcify and are centered on the IAC. On MR imaging, menigiomas will show a broad dural-base with an associated dural tail. Also, a CSF-vascular cleft can be seen between the tumor and brain parenchyma.

An epidermoid cyst is a congenital intradural lesion arising from inclusion of ectodermal epithelial elements during neural tube closure and is the third most common CPA mass. The main way to differentiate an epidermoid cyst from vestibular schwannoma, is that it appears as a nonenhancing CPA mass on T1 MRI with contrast, unlike vestibular schwannoma which will enhance. Epidermoids are insinuating masses with scalloped irregular margins that usually engulf cranial nerves (7th & 8th), vessels (AICA, vertebral artery). Other imaging findings on MRI is partial or absent attenuation on FLAIR imaging and diffusion restriction (high signal) DWI. 20% of epidermoids have calcification along the cyst-CPA margin on CT. Epidermoid cysts are also known as primary cholesteatoma or epithelial inclusion cyst.

An arachnoid cyst is an arachnoid or collagen-lined cavity that does not communicate directly with ventricular system or subarachnoid space. They commonly will push on the CPA angle but not enter the IAC. Imaging findings that distinguish it from vestibular schwannoma are lack of contrast enhancement and following CSF signal on all MR sequences. Arachnoid cysts also have an imperceptible cyst wall even with contrast enhanced MR or CT sequences.

Facial nerve schwannoma is a rare benign tumor of schwann cells that invest the peripheral facial nerve and can look exactly like a vestibular schwannoma. The best way to differentiate the two is to look for a labyrinthine segment tail in the facial nerve canal. When lesions are large they can appear as "ice cream on ice cream cone" with comma-shaped "tail."


Actual diagnosis: Vestibular schwannoma (with communicating hydrocephalus)


Key points

Vestibular schwannomas (also known as acoustic schwannomas) are benign intracranial extra-axial tumors that arise from Schwann cell sheaths that invest the vestibular or cochlear nerve in cerebellopontine angle-internal auditory canal (CPA-IAC). Acoustic neuromas account for approximately 80% of tumors found within the CPA. The remaining 20% are principally meningiomas. In rare cases, a facial nerve neuroma, vascular tumor, lipoma, or metastatic lesion is found within the cerebellopontine angle.

Acoustic tumors, like other space-occupying lesions, produce symptoms by any of 4 recognizable mechanisms: (1) compression or distortion of the spinal fluid spaces, (2) displacement of the brain stem, (3) compression of vessels producing venous or arterial infarction, or (4) compression and/or attenuation of nerves.

Because the CPA is relatively empty, tumors can continue to grow until they reach 3-4 cm in size before they come in contact with important structures. Growth is often sufficiently slow that the facial nerve can accommodate to the stretching imposed by tumor growth without clinically apparent deterioration of function. Tumors that arise within the IAC may produce relatively early symptomatology in the form of unilateral sensorineural hearing loss or vestibular disturbance by compressing the cochlear nerve, vestibular nerve, or labyrinthine artery against the bony walls of the internal auditory canal.


Imaging findings

MRI

Gold standard for diagnosis is gadolinium enhanced T2 MRI of the brain and CPA-IAC.
MRI can detect masses as small at 2 mm.
T1WI: lesion will appear as an intermediate signal most commonly; a high signal foci will be present if there is a hemorrhagic lesion (which is rare).
T2WI: lesion will appear as a "filling defect" in high signal CSF of CPA-IAC cistern. Small lesions will appear as ovoid filling defect, where as larger lesions have an "ice cream on cone" shaped filling defect.
T1 C+: Focal, enhancing mass of CPA-IAC cistern.
ther MR findings: 0.5% associated arachnoid cyst.


CT with contrast

Well-delineated, enhancing mass of CPA-IAC cistern with no calcification.
Smaller intracanalicular lesions < 6 mm may be missed.

Scrofula

Findings

Figure 1 and Figure 2: Contrast-enhanced CT coronal reformatted images demonstrating bilateral, bulky cervical lymph nodes that are centrally hypodense, representing necrosis, with peripheral enhancement.
Figure 3, Figure 4, and Figure 5: Axial images showing the extensive volume of necrotic lymphadenopathy and medial displacement of major vascular structures.
Figure 6: A sagittal reconstruction highlights the confluent nature of the necrotic lymph nodes.


Diagnosis: Scrofula (infectious cervical lymphadenitis) caused by mycobacterium tuberculosis


Scrofula, or infectious cervical lymphadenitis, is a term predominantly applied to tuberculous and non-tuberculous mycobacterial infections (NTM) affecting the cervical lymph nodes. Humans are the only reservoir for M. tuberculosis. Other tuberculous bacilli that cause disease in humans are M. bovis, and M. africanum, which most often cause extrapulmonary disease. NTM are ubiquitous, and reside in the soil. They can be found in contaminated water, dairy products, eggs, dust, and even tap water. Approximately 95% of adult scrofula cases are caused by mycobacterium tuberculosis, while the remaining 5% are caused by NTM, such as M avium intracellulare, M scrofulaceum, M kansasii and M chelonei. In children, this statistic is reversed, with NTM responsible for up to 92% of scrofula cases.

Scrofula produces lymph nodes that are discrete, firm, and typically nontender, in contrast with the lymphadenopathy associated with acute infection that is often tender. A firm mass of matted nodes may become apparent with disease progression, and if untreated, lymphadenopathy can become fluctuant with draining fistulas. Enlarging nodes may compress the esophagus causing dysphagia. The presence of systemic symptoms is variable and more likely in immunocompromised patients.

Scrofula presents with a variable imaging appearance depending upon the stage of the disease. Tuberculous lymphadenitis may be unilateral (90% in adults) or bilateral and is usually found in the internal jugular nodal chains (levels 2 - 4) and the spinal accessory chains (levels 5a and 5b). In the early infectious phase, non-necrotic nodes have homogeneous signal intensity and enhance homogeneously with contrast on both CT and MR. As the disease progresses and nodes become necrotic, CT images demonstrate characteristic central low density, representing necrosis, with a thick rim of enhancement. Peripheral contrast enhancement reflects hyperemia of the inflamed lymph node capsule or increased lymph node vascularity. On MR images, the necrotic center of the nodes will show intermediate signal intensity on T1-weighted images, low signal intensity on T2-weighted images, and will enhance with contrast. The surrounding granulation tissue, with its inflammatory hypervascularity and increased vascular permeability, will be markedly hyperintense on T2-weighted images. The nodes may become multiloculated and matted, simulating metastatic cervical disease both on imaging and clinically. Despite extensive necrosis, infiltration of adjacent fat planes is minimal, which may differentiate this process from other infections or malignant nodal disease. Chronic or post-treatment nodes are characterized by fibrous and calcific elements that are easily identified on CT. Calcification can also be seen in scrofula caused by NTM. On MR, treated nodes are homogeneously hypointense on both T1 and T2-weighted images, and do not enhance with contrast.

Cervical lymph nodes enlarge in response to neoplastic, inflammatory, and systemic disease. The broad differential diagnosis of enhancing cervical lymphadenopathy in an adult includes, but is not limited to, metastatic squamous cell carcinoma, metastatic papillary thyroid carcinoma, lymphoma, tuberculous and nontuberculous mycobacterial lymphadenitis, cat-scratch disease, Kaposi sarcoma, AIDS-related lymphadenopathy, acute septic infection, Kimura disease, Castleman disease, and Kikuchi disease. Fungal infections and viral infections, such as Epstein-Barr virus, herpes simplex virus, cytomegalovirus, and rubella also may present with bilateral diffuse lymphadenopathy.

Diagnosis usually requires fine needle aspiration (FNA) for histologic examination and culture. Once scrofula is diagnosed, it is important to determine the exact etiology, as tuberculous scrofula is treated medically and NTM infections are treated surgically. Lymphadenopathy may initially worsen during antituberculous therapy, representing an immune response to killed mycobacteria. Surgical intervention is reserved for complications such as abscess formation and draining sinuses. The treatment of choice for NTM infections is complete surgical excision of all affected tissue.

Spinal schwannoma

Findings

61-year-old male with a multilevel intradural extramedullary lesion demonstrating isointensity on sagittal T1 (Figure 1), intense enhancement on sagittal T1 post gad (Figure 2) and sagittal T1 post gad fat sat (Figure 3), and high signal intensity on sag STIR (Figure 4).
Axial T1 pre contrast (Figure 5) post contrast (Figure 6) and post contrast with fat saturation (Figure 7) demonstrate an intradural extramedullary lesion compressing and displacing the thoracic cord to the left.

Differential diagnosis for intradural-extramedullary spinal mass lesions:
- Nerve sheath tumor
- Meningioma
- Metastasis
- Paraganglioma
- Vascular malformations
- Inflammatory process
- Developmental lesions


Diagnosis: Spinal schwannoma


Nerve sheath tumors and meningiomas are the two most common intradural-extramedullary spinal tumors, representing 30 and 25% of presenting lesions, respectively. Both are typically benign, slow-growing tumors which may be present for years before there is functional impairment. MRI is the modality of choice in distinguishing these pathologies.

Nerve sheath tumors compromise schwannomas and neurofibromas, most often present in the fourth and fifth decades of life, and may be associated with neurofibromatosis. Schwannomas arise from dorsal sensory roots, more commonly in the lower thoracic and lumbar areas. Neurofibromas, unlike schwannomas, involve the parent nerve, and are unencapsulated.

Meningiomas are the second most common intradural-extramedullary spinal tumor and are more common in women. Multiple meningiomas may also be associated with neurofibromatosis. Meningiomas are predominately located in the upper and mid- thoracic areas, different from schwannomas, but are in a similar distribution in the anterior-posterior plane. Both nerve sheath tumors and meningiomas can be found in a “dumbbell shape,” with both extra- and intradural components.

MRI is the modality of choice in the evaluation of intradural-extramedullary spinal tumors. Nerve sheath tumors and meningiomas demonstrate characteristics of craniocaudal location divergence, hyperintensity and heterogeneity of T2W images, intensity and heterogeneity of enhancement, and the presence or absence of the “dural tail sign”. Schwannomas are typically hyperintense and heterogeneous compared to meningiomas on T2W images. The tumors show different contrast enhancement- meningiomas enhance moderately and homogenously, while schwannomas enhance strongly and irregularly. The “dural tail sign,” a reactive thickening of dura tapering away from the tumor, is associated with meningiomas, though this is not a specific sign. Additionally, neural foraminal extension and foraminal widening is suggestive of schwannoma, while bony sclerosis surrounding the mass is suggestive of meningioma.
Vascular tumors may necessitate pre-operative angiography and embolization.

Type II spinal AVM

Findings

MRI Spine Thoracic: Focal area of low T2 signal with in the spinal cord at the T7 level. There is increased T2 signal within the surrounding cord without mass effect. No clearly abnormal T1 signal or enhancement is seen. No abnormal flow voids are present.
CT Chest: There is a tortuous vessel within the posterior spinal canal which enters at the T9-T10 level from the right and terminates in a blush of contrast at the T7 level in the spinal cord.
Angiogram: T8 arterial injection shows an abnormal vessel extending superiorly to the T7 level with a small nest of abnormal vessels and a very early draining vein which extends inferiorly to the T9-10 level.

Differential diagnosis:
- Cavernous angioma
- Ependymoma
- AVM
- AVF


Diagnosis: Type II spinal AVM


Key points

There are four types of spinal AVMs, this is a type II which means there is abnormal intramedullary vasculature with a nidus. Type III lesions are also true AVMs; they are just larger and more complex. Type I and IV lesions are actually AVFs. Type I is the most common spinal AVM; it is a dural arteriovenous fistula. Type IV is an intradural extramedullary AVF from spinal artery to the coronal venous plexus.
Type II AVMs are generally diagnosed in the early 20s. Patients have a progressive course of myelopathy with severe sudden neurologic deficits when the lesions hemorrhage. Males and females are equally affected.
MRI is very useful in localizing the lesion. A definitive diagnosis is difficult as in this case if the vessels are too small to be visualized. Angiography is the gold standard for making the diagnosis. Both CT and MRI can help with angiogram planning.
Treatment is often embolization with good responses; however, the lesions can return. Surgery is often performed in order to prevent reoccurrence of the lesion.

Uncal herniation with posterior cerebral artery occlusion and resulting infarct

Findings

Image 1: Acute intraparenchymal hemorrhage with midline shift.
Image 2: Effacement of the basal cistern, quadrigeminal plate with enlargement of the contralateral lateral ventricle.
Image 3: Followup study 2 weeks later demonstrates hypo density in the left posterior cerebral artery distribution.

Differential diagnosis:
- Uncal herniation with posterior cerebral artery occlusion
- New thrombotic infarct in the posterior cerebral artery distribution
- Edema from infarct not seen with initial imaging


Diagnosis: Uncal herniation with posterior cerebral artery occlusion and resulting infarct


Discussion

With increased intracranial pressure, the brain can herniate transtentorially, cutting off circulation to the posterior cerebral artery and causing infarct of the ipsilateral occipital lobe. Radiologic evidence of descending transtentorial herniation includes obstruction of the CSF draining system and contralateral enlargement of the lateral ventricle, the uncus extending into the suprasellar cistern, and ipsilateral prepontine cistern widening. The clinical evidence for herniation itself includes an ipsilateral dilated pupil and contralateral hemiparesis, though these may be difficult to discern in the setting of already increased intracranial pressure due to the underlying etiology. The sequelae of PCA infarct include acute vision loss, confusion, new onset posterior cranium headache, paresthesias, limb weakness, dizziness, nausea, memory loss and language dysfunction.


Radiologic overview of the diagnosis

There will be evidence for increased intracranial pressure such as a space-occupying lesion, hemorrhage or edema; and, more specifically, evidence for transtentorial herniation including mass effect with uncal extension into the suprasellar cistern and contralateral lateral ventricle expansion. Over a period of time, there will eventually develop ipsilateral or bilateral signs of infarct on MR or CT in the distribution of the posterior cerebral artery within the occipital lobe.

Frontal sinus mucocele

Findings

There is a large, expansile mass in the right frontal sinus crossing the midline, measuring 2.3 x 5.7 x 3.8 cm (AP, transverse, cephalocaudad dimensions). This mass extends inferiorly into the right orbit, pushing the right globe inferiorly and anteriorly. There is discontinuity of the ethmoidal margin. However, there is no definite extension of the mass into the brain parenchyma. These findings are consistent with a frontal sinus mucocele. Also noted is extensive sinus disease involving the other visualized paranasal sinuses.


Diagnosis: Frontal sinus mucocele


A mucocele is an encapsulated fluid collection which occurs due to obstruction of a paranasal sinus ostium. Obstruction of a sinus ostium can occur secondary to chronic sinus inflammation, trauma, surgery, chronic sinus polyposis and tumors such as an osteoma. In children, there may be a history of cystic fibrosis.

Mucoceles are important diagnoses to make due to their expansile nature. They have the ability to erode through adjacent bones, including the base of the skull to result in intracranial extension. Mucoceles can also involve the orbital cavity, resulting in proptosis and displacement of the globe. Orbital involvement may also affect branches of cranial nerve III. They can become inflamed and fill with pus (pyocele) or pus and mucus (mucopyocele). Clinically, patients experience symptoms which occur as a result of localized mass effect and inflammation. Depending on the extent of the mucocele and the paranasal sinus affected, patients may present with intractable headaches, orbital discomfort, decreased visual acuity, a visual field defect, and facial pain.

Plain film radiographs of the sinuses will reveal smooth, expansile enlargement of the affected paranasal sinus. The adjacent bone may also be thinned secondary to the expansile nature of the lesion. The sinus is typically completely opacified. Further work-up includes a CT of the maxillofacial bones, which will reveal a uniform non-enhancing, low-attenuating expansile mass in the paranasal sinus. There may be regions of hyperdensity within the lesion representing inspissated mucus. There may also be bone remodeling and thinning but without evidence for bone destruction. T1-weighted MR images depict mucoceles as an expansile and hyperintense abnormality of the affected paranasal sinus. T2-weighted MR images further characterize a mucocele as a hyperintense lesion with greater signal intensity than that seen on the T1-weighted images. The signal intensity will further depend on the state of hydration and contents within the mucocele (protein, hemorrhage, and calcification).

The preferred treatment of mucoceles is surgery with sinus reconstruction. Surgical treatment includes conservative options (marsupialization of the mucocele) and radical options (removal of the mucosa and obliteration of the sinus). If possible, it is important to re-establish sinus drainage to prevent mucocele recurrence. The resected mucosa may be normal or demonstrate areas of squamous metaplasia. Endoscopic sinus surgery has played a larger role in management of mucoceles in recent years. Despite surgery, mucoceles often recur, warranting long-term follow-up.

Dysembryoplastic neuroepithelial tumor (DNET)

Findings

Brain MRI shows T2 hyper intense lesion in a right parietal cortex with multiple small "cystic" components, extension into subcortical white matter. FLAIR hyperintense, but without perilesional edema or mass effect. No contrast enhancement.


Diagnosis: Dysembryoplastic neuroepithelial tumor (DNET)


Key points

Benign intracortical mass, superimposed on a background of cortical dysplasia.
Typical appearance: small, wedge-shaped "bubbly" mass which is based in a single gyrus, extends towards the ventricle. Characteristic features are a lack of mass effect, surrounding edema, or post-contrast enhancement. There should be little/no growth of the lesion over time.
Frequently scallops inner table of skull, sometimes calcifies, and infrequently hemorrhages. Associated cortical dysplasia is common.
Usually found in children/adolescents, comprises 1-2% of primary brain tumors (age <20). Patients commonly present with partial seizures. Most commonly location is in temporal lobe, followed by parietal cortex, caudate nucleus, septum pellucidum. From 5-80% of epilepsy brain specimens show DNETs.


Radiographic Findings

CT: Thickened gyrus, slightly hypo attenuating. May mimic acute ischemia.
MR: T1 - hypo intense with gyral architectural distortion. T2 - strikingly hyper intense, with bubbly cystic components, extends towards ventricle. FLAIR - characteristic "bright rim," but no perilesional edema. T1+C = minimal / no enhancement. DWI = no diffusion restriction.

Choroid plexus papilloma

Findings

MRI imaging demonstrates a large, 7 x 4 x 4 cm (craniocaudal, AP, and transverse) heterogeneous mass within the 4th ventricle, with associated marked obstructive hydrocephalus. This mass extends below the 4th ventricle into the foramen magnum. There is no significant surrounding cerebellar edema.


Diagnosis: Choroid plexus papilloma (pathologically proven)


Key points

Choroid plexus papilloma is a relatively rare pediatric intracranial neoplasm, accounting for approximately 3% of such tumors.
Most common in patients under 1 year of age, and more common in males.
Arise from cuboidal epithelium of choroid plexus.
Associated with Li-Fraumeni and von Hippel Lindau syndromes.
Increased intracranial pressure can result from both tumor secretion of CSF, as well as by CSF outflow obstruction due to the intraventricular mass.
Presenting symptoms may include headache, N/V, ataxia, visual changes, or drowsiness.
On CT and MR, typical findings include a heterogeneously enhancing mass, potentially with cystic areas. On CT, punctuate calcifications may be seen in up to 20% of cases.
Treatment is typically by attempted total resection.

Semilobar holoprosencephaly

Findings

Partial formation of the interhemispheric fissure and falx cerebri in the posterior portions of the brain. Fusion of the frontal lobes. Rudimentary temporal horns of the lateral ventricles. Absent septum pellucidum. Lack of a corpus callosum genu or anterior body. Partial fusion of the thalamus and caudate and hypothalamus are not clearly separated resulting in a small third ventricle.


Diagnosis: Semilobar holoprosencephaly


Key points

There are three types of holoprosencephaly: alobar, semilobar, and lobar.
Semilobar holoprosencephaly represents a congenital brain malformation with severity between alobar and lobar holoprosencephaly.
Clinical findings include microcephaly, macrocephaly, developmental delay, spasticity, or other motor abnormalities.
Imaging findings: Interhemispheric fissure and falx cerebri are partially formed posteriorly, and the anterior portions of the brain are fused and underdeveloped. Septum pellucidum is absent. The splenium of the corpus callosum is present with absence anteriorly of the genu. Anterior extent of corpus callosum formation correlates with remainder of the brain's formation. The hypothalami, caudate, and thalami are partially unseparated resulting in a small 3rd ventricle. Dorsal cysts may be seen, always when the thalami are fused.