CNS epidermoid

Findings

Lateral ventricles and third ventricle are dilated. A mildly heterogeneous low density mass involves the dorsal aspect of the midbrain near the anticipated position of the pineal gland and cerebral aqueduct . MR confirms a mass in the region of the cerebral aqueduct extending into the fourth ventricle inferiorly and superiorly into the region of the posterior third ventricle. Closely following CSF, the mass demonstrates decreased T1 signal and increased T2 signal. There is restricted diffusion. There is no associated abnormal enhancement on the C+ sagittal images.


Diagnosis: CNS epidermoid.


Discussion

Intracranial epidermoid represents up to 1.8% of all primary intracranial tumors. They are the most common congenital intracranial tumor. They represent the third most common CPA/IAC mass after schwannoma and meningioma.

They most commonly present with headaches and possibly with cranial nerve palsies, typically of the 5th, 7th, and 8th nerves. They may remain clinically silent for many years. There is no gender predilection. Their presentation peaks at age 40 and has a range of 20 – 60 years of age.
As the have epithelia components they grow slowly. They can cause chemical meningitis if they leak and rarely have been reported to undergo malignant transformation to squamous cell carcinoma.
Treatment involves microsurgical resection which can be complicated by encasement of surrounding structures. Recurrence is common if they are not completely resected and seeding of the subarachnoid space has been reported.


Radiologic Overview

Epidermoid typically follow CSF density and may encase surrounding structures. Most commonly they are found in the CP angle (40-50%). They can also commonly be found in the fourth ventricle and middle cranial fossa, typically para-sellar. Occasionally they can be found within the skull and spine.
CT findings: Most are hypo dense, although 10-25% will have calcifications. They typically do not show post contrast enhancement however may have minimal enhancement at the margin. There is a rare variant which may be dense secondary to hemorrhage or high protein.
MRI findings: Again they are similar to CSF on T1 and T2 pulse sequences. On T1 they are slightly hyper intense to CSF and on T2 they are isointense to slightly hyper intense to CSF. Intensity will be altered depending on the cyst contents. Minimal enhancement can be seen at the margins. They key distinguishing feature is the appearance on diffusion weighted images which is markedly intense, "light bulb bright". On ADC mapping they are isointense to brain parenchyma.
The differential diagnosis includes arachnoid cyst, which follow CSF signal on all sequences and does not show restricted diffusion. Arachnoid cysts typically displace adjacent structures whereas epidermoid lesions encase them. Cystic neoplasm's often enhance and do not follow CSF signal. Dermoid cysts are typically heterogeneous on MR and more closely follow fat signal characteristics. Additionally dermoid are typically midline. Inflammatory cysts typically enhance and have surrounding edema and/or gliosis.

Sturge-Weber syndrome

Findings

Gyriform calcifications are observed over the left occipital lobe in the CT exam. The MRI demonstrates atrophy of the left cerebral hemisphere. There is enlargement of the left choroid plexus which demonstrates homogeneous enhancement post contrast. There is also gyriform enhancement post contrast most significantly on the left occipital lobe. There is diffuse enhancement of the subcutaneous tissues over the left eye.


Diagnosis: Sturge-Weber syndrome.


Key points

Classically the patients have a facial port-wine stain, ipsilateral intracranial abnormalities, contralateral hemiparesis, hemiatrophy, mental retardation, and homonymous hemianopia. The severity of these features varies widely patient to patient. Commonly the patients will have glaucoma on the affected side. Seizures are also very common.
Only 8% of patients with port-wine stains have Sturge-Weber Syndrome. 13% of Sturge-Weber syndrome patients do not have a facial angioma.
There is no clear genetic link at this time. There is no sex or race Predilection and it is very seldom seen more than once in the same family. Several different chromosomal abnormalities have been implicated.
Radiographically one can see "tram track calcifications" which are leptomeningeal calcifications like those seen on the CT image.
MRI can demonstrate the angiomatous abnormalities. In this case the cutaneous capillary angioma (port-wine stain) is well demonstrated as is the meningeal angiomatosis over the left occipital lobe. Cerebral hemiatrophy is well demonstrated by MRI as is the choroidal angiomatosis.
Multiple therapies are employed in these patients. The port-wine stains can be "removed" with laser treatments. Seizures can be treated with anticonvulsants. Refractory seizures can be treated surgically. The surgeries can be as extensive as a hemispherectomy.

Intraosseous cavernous hemangioma of the left maxillary bone

Findings

Noncontrast orbital CT demonstrates a mass arising from the left maxillary bone with internal bony trabeculations in a “honeycomb,” “sunburst,” or “spokewheel” pattern typical for an intraosseous cavernous hemangioma.
This pattern of trabeculation on CT translates into a network of linear hypointense T1 and T2 signal with interspersed areas of enhancement on the T1 post gadolinium images characteristic of this entity.


Diagnosis: Intraosseous cavernous hemangioma of the left maxillary bone


Intraosseous cavernous hemangiomas are benign neoplasms which comprise only up to 1% of all osseous tumors and 7-10% of skull tumors. These are most frequently seen in the frontal and parietal bones with the orbital and maxillofacial bones infrequently involved. These tumors are slow growing and are generally asymptomatic unless they cause mass effect on sensitive structures such as within the intraorbital compartment. In symptomatic cases, en bloc resection is generally the treatment of choice. Preoperative angiography with potential embolization may be helpful as these tumors can bleed profusely.

Clinical differential diagnosis includes fibrous dysplasia, osteoma, dermoid cyst, meningioma, eosinophilic granuloma, Lagerhan cell histiocytosis, and metastatic disease. On imaging, these tumors are well-defined and have characteristic internal trabeculations and enhancement features described as a “honeycomb,” “sunburst,” or “spokewheel” pattern. Malignant degeneration is rare.

Petrous apex chondrosarcoma

Findings

The head CT (bone windows) demonstrates a region of bony destruction extending from the right petro-occipital fissure into the carotid canal. The axial T2 images demonstrate a hyper intense, extra-axial, right petrous apex mass that extends from the petro-occipital fissure to the cavernous sinus. The margins of the mass are lobulated, and it encases the cavernous internal carotid artery. The axial T1 contrast-enhanced images demonstrate intense enhancement of the mass.


Diagnosis: Petrous apex chondrosarcoma


Key points

Classic MR imaging appearance of petrous apex chondrosarcoma is a mass located at the petro-occipital fissure with high T2 signal intensity that heterogeneously enhances.
The CT shows chondroid mineralization in 50%.
Invasive bone changes at the petro-occipital fissure strongly favors the diagnosis. Greater than 50% will have associated bone destruction.
2/3 located at the petro-occipital fissure, 1/3 located at the anterior basis sphenoid
Usually has lobulated margins
High T2 signal, low to intermediate T1 signal
Heterogeneous enhancement with contrast; whorls of enhancement within tumor matrix are often seen
Often displaces or encases the ICA
Classic presentation is a CN 6 nerve palsy. Other CN palsies can occur less commonly (3, 5, 7, 8—3, 4, and 6 are possible with cavernous sinus invasion)


Differential diagnosis
- Metastatic tumor
- Chondrosarcoma
- Plasmacytoma
- Nasopharyngeal cancer
- Chordoma
- Cholesteatoma
- Calcified meningioma
- Chondromyxoid fibroma

Distinguishing characteristics from other entities in the differential:
- Metastatic tumor – Can have a similar appearance; breast cancer and prostate cancer are two of the most common tumors to metastasize to the petrous apex
- Plasmacytoma - Usually intermediate T1 and T2 signal; usually more midline
- Chordoma - Similar appearance to chondrosarcoma but often see tumor "thumb" indenting the anterior pons; often midline
- Cholesteatoma - Does not enhance but has an otherwise similar appearance
- Calcified meningioma – Not typically destructive; low to intermediate T2 signal
- Chondromyxoid fibroma - Similar MR appearance to chondrosarcoma; areas of ground glass density can be seen on CT

Persistent trigeminal artery (PTA)

Findings

There is an aberrant artery arising from the cavernous segment of the right internal carotid artery, coursing posterior and medial to terminate in the basilar artery. The basilar artery is diminutive below the level of this vessel and is normal in caliber above it.


Differential diagnosis

Variant caroticobasilar anastomosis
- Persistent trigeminal artery (PTA)
- Persistent hypoglossal artery (PHA)
- Persistent otic artery (POA)
- Fetal origin of the posterior cerebral artery (FOPCA)


Diagnosis: Persistent trigeminal artery


Key points

Persistent right trigeminal artery (PTA) is the most common (0.1 - 0.2% of angiograms) of a group of persistent embryonal carotid-basilar artery anastomoses.
Multiple transient connections occur consecutively in fetal life between the carotid and vertebrobasilar circulations (named according to the cranial nerve they parallel):

- Proatlantal intersegmental artery – connects cervical ICA (C2-C3) to the vertebral artery between C1 and the occipital bone
- Persistent hypoglossal artery – cervical ICA (C1-C2) and proximal (caudal) basilar artery; 2nd most common
- Persistent otic artery – petrosal ICA to proximal basilar artery via the internal acoustic meatus; very rare; vertebral arteries may be absent or hypoplastic
- Persistent trigeminal artery – cavernous ICA to distal basilar; may see enlargement of the basilar above the level of this artery; supplies basilar before the vertebral and posterior communicating arteries develop.

Clinical significance: 25% prevalence of other vascular abnormalities (e.g. aneurysms)
Usually asymptomatic but may present with mass effect on adjacent structures like the pituitary and cranial nerves.
No treatment needed if asymptomatic.

Mondini malformation

Findings

Non-contrast axial CT images through the temporal bones demonstrate incomplete partitioning of the left cochlea and nonvisualization of the modiolus resulting in confluency between the middle and apical segments. Compare this to the right cochlea, which is normal. There is also abnormal dilitation of the left vestibular aqueduct.


Diagnosis: Mondini malformation


Case points

Mondini malformation occurs when there is abnormal development of the cochlea resulting in less than 2.5 turns and incomplete formation of the modiolus.
It is a cause of sensorineural hearing loss.


Discussion

Mondini malformation refers to an anomaly of the cochlea in which the modiolus fails to develop properly in the seventh week of fetal life, resulting in a cochlea with only 1.5 turns instead of the normal 2.5 turns. In addition, the interscalar septum between the middle and apical segments fails to form leading to a confluent, sac-like cochlea. There is an association with an enlarged vestibular aqueduct and anomalies of the vestibules and semicircular canals. In some cases, Mondini malformation may also be associated with Pendred Syndrome (bilateral sensorineural hearing loss and goiter)

Patients present with gradual or sudden sensorineural hearing loss with preservation of high-frequency hearing because the basal turn of the cochlea is usually preserved. These patients are also at increased risk for developing meningitis or perilymphatic fistula.

Treatment revolves around clinical presentation. Cochlear implants may be used to enhance hearing while middle ear infections are treated aggressively due to the increased risk for meningitis.

Acrania

Findings

Figure 1 and Figure 2: Coronal and axial ultrasound images of the fetal head show an absent cranial vault and an abundant amorphous mass of brain tissue. Normal cranial vault appears as bright echogenic lines characteristic of bone which is absent here.


Diagnosis: Acrania

Acrania is a rare congenital anomaly in which the flat bones of the cranial vault are partially or completely absent with complete but abnormal development of the cerebral hemispheres. The condition is identified by the absence of the calvarium. The cerebral hemispheres are surrounded by a thin membrane. The demonstration of abundant, abnormal brain tissue on the sonogram helps differentiate cases of acrania from the more common anencephaly.
Acrania is thought to occur because of abnormal migration of mesenchymal tissue, which normally covers the cerebral hemispheres. This faulty migration results in the faulty formation of the cranial bones, muscles, and dura mater. Ossification of the fetal cranium begins and accelerates after 9 weeks. The important ultrasound feature is an absent cranium, which allows diagnosis from 11 weeks onward. At 11-14 weeks gestation, the majority of cranial ossification is in the lateral aspects of the frontal bones and lower parietal bones, and no vault ossification is visible in the midline on a perfect midsagittal image. Misdiagnosis may occur if only midsagittal views of the fetus are obtained. The absence of cranial ossification may not be noted on routine examination, and the head may appear relatively normal. It is important to look specifically for frontal bone ossification in the axial and coronal planes.
The differential diagnosis includes anencephaly, large cephaloceles, hypophosphatasia and osteogenesis imperfecta. Anencephaly and acrania may commonly be confused with each other early in the pregnancy. Typically there is a progression in utero from a relatively normal appearing brain, to an amorphous brain mass, to no recognizable brain tissue which is the key to diagnosis of anencephaly in the second and third trimesters. In the first trimester, the brain of affected fetuses may appear relatively normal or may demonstrate varying degrees of distortion which can lead to confusion of accurate diagnosis. With anencephaly, the cerebral tissue is completely absent. With cephaloceles, the cranial vault can always be detected and a part of the brain is intracranial. Certain conditions such as hypophosphatasia and osteogenesis imperfecta can mimic acrania due to the lack of mineralization of the skull bones. With these conditions the intracranial anatomy is normal and the brain is surrounded by a thick layer of tissue representing soft tissues and unossified bone. Other findings such as bowing, shortening, or fractures of long bones are usually also present and aid in distinction from acrania.
Acrania is a lethal malformation. Antenatal identification allows the clinician to make appropriate and timely management decisions.