Nasal dermoid sinus with cyst

Findings

CT show a hyper dense mass within the lower anterior interhemispheric fissure. MR confirms the extra-axial mass within interhemispheric fissure. The mass is isointense on T1, hyper intense on T2 and does not exhibit restricted effusion. There is a tract identified extending from the bridge of the nose to the lesion, best seen on sagittal images. Mild peripheral enhancement of the lesion is noted following the administration of intravenous contrast.

Differential diagnosis for extra-axial mass in the interhemispheric fissure:
- Nasal dermal sinus with epidermoid/dermoid
- Fatty marrow in cristi galli
- Nasofrontal cephalocele
- Meningioma

Findings are most compatible with a nasal dermal sinus tract with a cyst within the interhemispheric fissure. The mass is felt to be more compatible with a cyst rather than a dermoid or epidermoid because it does not have signal characteristics of fat as seen with with a dermoid, or exhibit increased signal intensity on diffusion like an epidermoid. There is no evidence surrounding edema.


Diagnosis: Nasal dermoid sinus with cyst (presumed diagnosis).


Key points

Nasal dermoid sinus is a result of defective embryology of the anterior neuropore resulting in any combination of sinus tract with epidermoid/dermoid.
Typical presentation is a young child with pit on the skin of nasal bridge.
Other clues to the diagnosis is a bifid cristi galli and enlarged foramen cecum.
Predisposes to recurrent meningitis if left untreated.
Treatment is surgical excision.

Odontogenic keratocyst

Findings

Multiple CT axial views of the mandible show a well corticated expansile cystic lesion with somewhat scalloped borders containing a comminuted pathologic fracture.
Figure 1: Comminuted pathologic fracture of an expansile lesion with well defined margins in the left mandible.
Figure 2: Soft tissue density likely secondary to protein/blood products.


Diagnosis: Odontogenic keratocyst


Odontogenic keratocysts also known as primordial cysts arises from remnants of dental lamina and make up 10% of jaw cysts. They occur more commonly in the 2nd to 4th decades and have a 2:1 M:F predilection.

75% are located in the posterior mandible around the 3rd molar. The most common maxillary location is the canine region. 50% are lucent, unilocular with well-defined sclerotic margins. Many cysts are expansile and multilocular.

The pathology demonstrates remnants of dental lamina. They are comprised of a fibrous wall lined by squamous epithelium with a low protein content. The cysts could have a low attenuation on CT likely due to low protein content or a high attenuation from hemorrhage. Theses cysts make up 10% of jaw cysts and are associated with Noonan and Marfan syndrome. A minority of odontogenic keratocysts are multiple and 50% of these cases will have associated basal cell nevus.

Approximately 50% of patients are symptomatic with jaw swelling being the most common symptom, seen in up to 85% of symptomatic patient. Other signs and symptoms include sinus tract with drainage seen in 15%, pain, paresthesia and trismus.

The natural history of odontogenic keratocysts are rapid growth with high recurrence rate. Treatment is with enucleation and aggressive curettage. Due to high recurrence rate follow up studies are recommended.

CNS dermoid

Findings

Along the posterior aspect of the midbrain there is exophytic focus of hyper intense T1 and heterogeneously hyper intense T2 signal which is heterogeneously hypo intense on T2 with fat suppression. This small mass heterogeneously enhances on T1.

Differential diagnosis:
- Dermoid
- Lipoma


Diagnosis: CNS dermoid.


Key points: Inclusion tumors (epidermoid and dermoid)

Congenital tumors resulting from abnormal incorporation of ectodermal elements during neural tube closure
Benign
Not neoplastic
Slow-growing
1% of intracranial tumors
Epidermoid 7x more common than dermoid


Epidermoid (cholesteatoma)
- Histopathology: Squamous epithelium, keratin, cholesterol
- No fat or calcification
- Cystic lesion filled with accumulating desquamated epithelium and cholesterol
- Typically conforms to enclosing space and surrounds structures
- Occasionally has mass-effect
- Less complex and thinner wall than dermoid
- Rupture is rare
- Location—off midline, most commonly at CPA (cerebellopontine angle)
- Imaging:
No contrast enhancement
Follows CSF on CT and MR but bright on FLAIR and diffusion
Differential diagnosis: arachnoid cyst


Dermoid
- Histopathology: Epidermoid + hair, fat, and sweat glands, calcification common, with arc-like calcification in 20%
- Contains ectoderm + dermal appendages (hair, sebaceous/sweat glands/secretions, desquamated keratinized epithelium)
- Predominantly fatty
- More complex and thicker wall than epidermoid
- Associated with dermal sinus tracts
- Rupture
Into subarachnoid space
Causes serious, potentially fatal, chemical meningitis (with vasospasm)
Larger lesions have higher rupture rate
- Location—midline, most commonly in spinal canal
- Imaging
Enhances if infected and especially with meningitis following rupture
Mimics fat on CT and MR with heterogeneity secondary to soft tissue
Differential diagnosis: lipoma

Crossed Cerebellar Diaschisis (CCD)

Findings

CT: Post-craniotomy surgical changes with vasogenic edema extending from left frontal lobe into left parietal and temporal lobes. There is symmetric cerebellar atrophy without evidence of asymmetric right hemispheric volume loss.
PET/CT: Decreased metabolism in left frontal lobe and right cerebellar hemisphere representing crossed cerebellar diaschisis.
MR: Enhancement throughout much of the remaining left frontal lobe, with extension into the right frontal lobe, basal ganglia, and the genu of the corpus callosum.
MRI: While PET/CT and MRI findings were suggestive of radiation necrosis, tissue biopsy showed evidence of recurrent malignant oligoastrocytoma (WHO grade 3). Cerebral lesion was subsequently resected surgically.


Diagnosis: Crossed Cerebellar Diaschisis (CCD) in a patient with radiation necrosis and recurrent malignant oligoastrocytoma (WHO grade 3)


Crossed cerebellar diaschisis (CCD) is a functional reduction in the cerebellar hemisphere contralateral to a cerebral lesion. It has been observed following strokes, intracranial tumors, epilepsy, and various types of intracranial trauma. There is a direct relationship between the incidence of CCD and increasing lesion size. CCD can range from a potentially reversible finding (typically following an acute stroke) to permanent degeneration. While most frequently associated with frontal lobe pathology, CCD can also be present with lesions involving the thalamus, basal ganglia, and the internal capsule. The cerebropontocerebellar pathway is thought to be the etiology of CCD; its interruption leading to a reduction in oxygen metabolism and glucose uptake in the contralateral cerebellar hemisphere that can be demonstrated with PET imaging. Conventional CT and MRI studies often do not show any abnormalities, as diaschisis does not always produce structural alterations.

Mycotic aneurysm at origin of superior cerebellar artery with pontine infarct

Findings

Brain MR demonstrates abnormal signal intensity in the right pons on FLAIR and restricted diffusion of the right pons. MR angiography and CT angiography demonstrate a small 3 mm aneurysm at the origin of the right superior cerebellar artery. At the time of embolization three days later, the aneurysm had significantly grown in size. It was successfully embolized.


Diagnosis: Mycotic aneurysm at origin of superior cerebellar artery with pontine infarct (the patient had known bacterial endocarditis, presumably caused by an untreated infected wisdom tooth)


Discussion

A mycotic or infectious aneurysm is caused by bacterial infection of a vessel resulting in a rapidly growing aneurysm. These are usually located at branch points of vessels. Atherosclerotic aneurysms, conversely, do not have such rapid growth. Infectious aneurysms are usually associated with bacterial endocarditis. Primary infectious aneurysms have an unidentified source. Secondary infectious aneurysms arise from a specific source of infection, like bacterial endocarditis or tuberculosis.

Bacterial aneurysms are usually saccular and have associated thinning of the vessel wall and perivascular inflammation. They are caused by septic emboli which infarct the vasa vasorum, causing necrosis of the vessel wall and development of a pseudoaneurysm. Mycotic aneurysms can demonstrate arterial stenosis near the aneurysm, multiple aneurysms, and rapid changes in morphology.

High mortality, around 70%.

Endovascular treatment can involve either parent artery occlusion or coiling of the aneurysm. For this patient, the coiling of aneurysms of the superior cerebellar artery can have complications of ischemia of the cerebellar cortex if the superior cerebellar artery is occluded. However, there is usually collateral vascular flow from the AICA and PICA through the vermian arcade. Aneurysmal coiling should include not only the parent vessel, but also include any tiny vessels that near the aneurysm that are feeding the aneurysm wall, to prevent refilling of the aneurysm with blood. Tight packing of a mycotic aneurysm could lead to rupture since the wall is very fragile, therefore, concomitant occlusion of the parent vessel should be considered.

Man-in-the-barrel syndrome (MIBS)

Findings

Figure A: Axial FLAIR shows bilateral symmetric high intensity signal in the centrum semiovale.
Figure B: Axial T2 weighted shows bilateral symmetric high intensity signal in the same areas.
Figure C: Axial DWI shows bilateral symmetric restricted diffusion in the same areas.
Figure D: Axial ADC shows restricted diffusion in the same areas.


Diagnosis: Man-in-the-barrel syndrome (MIBS)


The term man-in-the-barrel syndrome (MIBS) was coined by Sage in 1983 to describe the association of several clinical features which often occur together in patients with disproportionate weakness of both arms (especially proximally) and relatively normal mobility of face and legs, as though the trunk of the patient is stuck in a barrel. Since then, there have been multiple case reports in the literature describing observed MIBS believed to be caused by severe systemic hypotension related to emergent CABG , hemorrhagic shock , and severe anaphylaxis. Bilateral ACA-MCA watershed infarcts may be a common factor in all of these clinical scenarios. However, there have also been several reports of processes other than watershed infarcts with a clinical presentation similar to MIBS, including motor neuron diseases, pontine myelinolysis, glioma and vertebral artery dissection.

The dominant mechanistic theory explaining MIBS is that of bilateral symmetric watershed infarction in the region perfused by medullary arteries from the superficial pial plexus and deep penetrating arteries from the basal cerebral arteries, which has been known for at least 40 years. A related neurological entity, brachial diplegia due to pyramidal tract involvement was first described by Mohr in 1969. Although there have been several papers decribing the CT or MR features of watershed infarcts between the territories perfused by MCA and ACA, especially the corona radiata and centrum semiovale, it is unclear exactly which focal neural pathway is disrupted that directly leads to the clinical presentation of MIBS. It is postulated that there is a threshold for the amount of confluently affected paraventricular white matter above which MIBS may become manifest.

Despite the uncertainties mentioned above, MIBS remains a fascinating clinical phenomenon. Further research will hopefully better define this entity.

Marchiafava-Bignami syndrome

Findings

CT Head reveals hypo attenuation of the splenium and posterior aspects of the corpus callosum. Brain MRI reveals T2 prolongation of the entire corpus callosum, subcortical white matter, medial cerebellar hemispheres, and ventral medulla. There is a small right occipital subdural hematoma. There was no post-contrast enhancement.

Differential diagnosis:
- Marchiafava-Bignami syndrome
- Lymphoma
- Demyelinating disease
- Viral encephalitis
- Wernicke's encephalopathy
- Glioblastoma multiforme


Diagnosis: Marchiafava-Bignami syndrome


Key points

MB is primary degeneration of the corpus callosum. Other white matter tracts may be involved (as in this case).
First described in 1903 by two Italian pathologists, who found necrosis of the corpus callosum on autopsy in 3 alcoholic men that had recently died from seizures.
Initially thought to be caused by excess red wine consumption, now known to be related to vitamin B deficiency, generally seen in alcoholics.
Patients present with confusion, neurocognitive defects, and seizures.
Most patients with acute symptoms go into coma and die.
Chronic symptoms are characterized / accompanied by chronic dementia.
MB typically affects the body of the corpus callosum first, followed by the genu, and finally the splenium. Other white matter tracts may be involved.
On cytopathology, the middle layer of the corpus callosum is most affected.
On MR, disease revealed by areas of low T1 signal and high T2 and FLAIR signal. Signal intensity in the body of the corpus callosum at times extending into the genu and adjacent white matter.
Lesions do not enhance, unlike in glioblastoma, lymphoma, or encephalitis.
On CT, lesions are hypoattenuating.