Cholesterol granuloma of petrous apex

Findings

Figure 1 and Figure 2: Axial and coronal noncontrast CT show non-aggressive expansile lesion of petrous apex. Loss of cortical contiguity with maintenance of a thin rim of cortex in some locations indicates a slowly enlarging benign process.
Figure 3: Axial T1WI MR shows homogeneous high signal with well-defined margins. This lesion expands the petrous apex medially.
Figure 4: Axial T2WI MR reveals homogeneous internal high signal. Note the dark peripheral ring around this lesion consistent with hemosiderin deposition.
Figure 5: High signal on FLAIR.
Figure 6: Coronal T1 weighted image following contrast demonstrates increased signal, without enhancement, consistent with cholesterol granuloma.


Diagnosis: Cholesterol granuloma of petrous apex


Cholesterol granuloma is thought to arise in the mastoid air cells as a result of inadequate ventilation in the setting of otitis media and eustachian tube dysfunction. Hemorrhage in these cells with stasis leads to an inflammatory response with giant cell reaction and bony erosion. Cholesterol granuloma contains brownish fluid with cholesterol crystals. These lesions may be present in the middle ear as well as within the mastoid air cells and petrous apex. Several additional terms are used for these lesions. A cholesterol granuloma at the petrous apex is also called a giant cholesterol cyst. A cholesterol granuloma present in the mastoid is also called a chocolate cyst or blue-dome cyst.

Cholesterol granulomas are bright on all spin-echo sequences, which differentiate them from cholesteatomas. High internal T1 signal is secondary to presence of hemorrhage, blood break-down products, and cholesterol crystals. The primary reason is most likely the presence of paramagnetic intracellular methemoglobin. On T1 post contrast images, the peripheral enhancement may be difficult to appreciate as it is adjacent to an inherent T1 bright lesion. There is no internal enhancement. On T2, there is high internal signal with a peripheral dark hemosiderin ring. Because the lesions are inherently bright on T1, contrast is not very helpful in delineating the diagnosis. MRA is useful for surgical planning, such as assessing for encasement of the petrous ICA. On non contrast CT, the lesions are well defined and smoothly expansile. Faint peripheral enhancement may be present on contrast enhanced CT. CT is useful to evaluate bony destruction and involvement of the adjacent otic capsule and carotid canal. MR is more sensitive than CT for evaluation of recurrence. Increasing T1 signal in the post-operative petrous apex suggests recurrence.

Cholesterol granulomas occur in young to middle-age adults. The most common symptom is sensorineural hearing loss. Other presenting symptoms include tinnitus, hemifacial spasm, facial numbness, trigeminal neuralgia, and abducens palsy.

Cholesterol granulomas have no cyst wall and do not require complete surgical excision. Traditional treatment is drainage with establishment of a permanent ventilation system via a transtemporal approach. Often, silicone tubing is used to stent the drainage system and prevent stenosis. Reported recurrence rate is as high as 60%. The extended middle cranial fossa approach with extradural removal of cholesterol granuloma and obliteration of its cavity has a significant decrease in recurrence rate.

The differential diagnosis of cholesterol granuloma is cholesteatoma. Because they often coexist, confusion in terminology between cholesterol granuloma and cholesteatoma has been noted by many authors. Cholesteatomas are either congenital or acquired and thought to originate from from trapped skin and contains keratin debris, keratinizing squamous epithelium, and fibrous stromal subepithelium. By MRI, cholesteatomas are hypointense or isointense on T1-weighted images and hyperintense on T2 images. It is important to differentiate between cholesterol granuloma and cholesteatoma because of treatment differences. Cholesteatomas, regardless of size, require complete surgical removal.

Microtia

Findings

Figure 1: On the right, the mastoid air cells are under pneumatized. There is no identifiable external auditory canal.
Figure 2: A thick bony plate is visualized in the expected area of the external auditory meatus.
Figure 3: The facial nerve is identified.
Figure 4: There is a small amount of bone in the attic of the middle ear cavity but no formed malleus or incus is identified. This suggests rudimentary and/or hypoplastic ossicles. However, a normal morphology and location of the stapes is seen. The internal auditory canal is normal in caliber.
Figure 5: The apical and basal turns of the cochlea are within normal limits.


Diagnosis: Microtia


Microtia, which is a congenital deformity of the pinna and occurs more commonly in boys, is seen 1 in 8,000-10,000 births. It can be unilateral or bilateral. The etiology is unknown, but related to a variety of genetic factors. It is associated with other congenital syndromes, such as Townes-Brocks syndrome, Nager syndrome, and Miller syndrome. Some clinicians consider microtia to be a manifestation of the oculo-auriculo-vertebral spectrum (OAVS), where there are also facial, vertebral, and renal abnormalities. Renal abnormalities usually warrant a renal ultrasound, looking for abnormalities such as renal agenesis, hypoplasia, and crossed ectopia.

Microtia can be graded as follows:
- Grade I: A slightly small ear with identifiable structures and a small but present external ear canal
- Grade II: A partial or hemi-ear with a closed off or stenotic external ear canal producing a conductive hearing loss
- Grade III: Absence of the external ear with a small peanut vestige structure and an absence of the external ear canal and ear drum
- Grade IV: Absence of the total ear or anotia

Imaging of microtia is largely performed to form a template for further management options. Initially, a CT scan of the head (and/or temporal bones) is used to evaluate the exact middle and inner ear anatomy. Further staging by CT is recommended in order to avoid lesions to the facial nerve which most often can be displaced from its original location in patients with microtia, and also to assess for prognosis. In those patients being evaluated for surgical intervention, the following structures should be evaluated for planning surgery: the external auditory canal, bones (temporal, zygomatic, and the mandibular condyle), vessels (carotid canal, sigmoid sinus, and the jugular bulb), tensor tympani muscle and grade of mastoid pneumatization, ossicles, cochlear turns, vestibule, semicircular canals, facial nerve canal, and finally, the internal auditory canal. These pre-operative images substantially reduce the risk of facial nerve palsy, bleeding and worsening of hearing.

On axial CT images of the head, one can evaluate for either stenosis or complete atresia of the external auditory canal. At the same time, bone erosion by a secondary cholesteatoma or epidermoid cyst can be identified. One study showed the tympanic and/or mastoid portions of the temporal bone as commonly hypoplastic on CT images of patients with microtia. Dysplasia of the mandibular condyle and the zygomatic arch were also shown. Changes of the ossicles are frequently present and include dysplastic shape, diminution, thickening, axis rotation, or complete absence. Occasionally, the lateral semicircular canal is hypoplastic in patients with severe middle ear involvement. The internal auditory canal is rarely dysplastic in patients with microtia.

Microtia repair is complex. Testing is done initially to determine whether hearing is normal. If hearing is normal and a canal is not visible externally, a CT will be done to determine whether a rudimentary canal exists. The earliest age surgery can be attempted is three years, but will vary according to the graft material used. In some cases, patients may have to wait as long as 6 years of age. Exploration involves cautiously avoiding the facial nerve while drilling a canal through solid bone. A cartilage framework, usually derived from costal cartilage, is created and anchored beneath the skin of the mastoid area. Once it is well attached to the surface skin, a post-auricular crease is created in a second operation.

Vanderknaap disease - Megaloencephalic leukoencephalopathy with subcortical cysts (MLC)

Findings

Figure 1: Subcortical CSF intensity cyst in superior frontal and parietal lobe. Normal cerebellum.
Figure 2: CSF intensity subcortical cyst in superior parietal and anterior temporal lobe.
Figure 3: Diffusely swollen white matter (blue arrow). Preserved gray matter. CSF intensity subcortical cyst in anterior temporal lobe.
Figure 4: Diffusely swollen white matter. Preserved gray matter.
Figure 5: Cavum septum pellucidum. CSF intensity subcortical cyst in superior frontal and anterior temporal lobe. Normal basal ganglia.
Figure 6: Cavum septum pellucidum. CSF intensity subcortical cyst in superior frontal and anterior temporal lobe. Normal basal ganglia.


Diagnosis: Vanderknaap disease - Megaloencephalic leukoencephalopathy with subcortical cysts (MLC)


Vanderknaap disease is newly described rare leukoencephalopathies includes:
- 1. MLC - Megaloencephalic leukoencephalopathy with subcortical cysts
- 2. VWM - Leukoencephalopathy with vanishing white matter
- 3. WML - White matter disease with lactate
- 4. H-ABC- Hypomyelination with atrophy of the basal ganglia(BG) and cerebellum

Megaloencephalic leukoencephalopathy with subcortical cysts (MLC) is a rare leukoencephalopathy with an autosomal recessive mode of inheritance. The disease is relatively prevalent among Turkish people and in a certain Asian-Indian community, the Agarwal ethnic group.


MRI Features

In MLC the cerebral hemispheric white matter is diffusely abnormal and swollen. There are almost invariably subcortical cysts in the anterior temporal region, often also in the frontal and parietal subcortical regions The cysts are bilateral. The cysts tend to become larger with age and may increase in number. In some patients they become very large, The signal intensity of the contents of the cysts is always similar to that of CSF. Cortical gray matter structures,corpus callosum and basal nuclei are always normal. A patent and enlarged cavum septi pellucidum and cavum vergae are often present.

Similar white matter changes with swelling have been reported in Canavan disease, Alexander disease, L-2-hydroxyglutaric aciduria, and merosin-deficient congenital muscular dystrophy. However, in Canavan disease, as a rule, MRI demonstrates additional involvement of the thalamus and globus pallidus, not found in MLC patients. Special MRI findings in Alexander disease are a more prominent sparing of parieto-occipital white matter and often also sparing of the U fibers throughout. Basal ganglia and brain stem structures are typically involved. Cavitation starts in the deep frontal white matter. None of these features is present in MLC. In L-2-hydroxyglutaric aciduria MRI shows additional involvement of caudate nuclei, putamen, dentate nuclei, and severe atrophy of the cerebellar vermis, not observed in MLC. The MRI abnormalities observed in merosin-deficient congenital muscular dystrophy are very similar to those observed in MLC.

Subependymal giant cell astrocytoma (SEGA)

Findings

Figure 1: Axial noncontrast CT image shows an intraventricular mass near the foramen of Monro with foci of calcification, as well as several calcified subependymal nodules along the lateral ventricular surface. Hydrocephalus is also present with enlargement of the right lateral ventricle.
Axial T2-weighted and FLAIR MR images demonstrate a mass near the foramen of Monro with heterogenous, somewhat hyperintense signal compared to white matter. Intense homogeneous enhancement is seen on contrast-enhanced axial and coronal T1 weighted images. Subependymal nodules are seen along the lateral ventricles. Multiple foci of increased signal are seen on FLAIR images in the subcortical regions representing parenchymal tubers.


Diagnosis: Subependymal giant cell astrocytoma (SEGA)


Subependymal giant cell astrocytomas are intraventriclar neoplasms that occur in 15% of patients with tuberous sclerosis. Tuberous sclerosis (Bourneville’s disease) is a neurocutaneous phakomatosis characterized by an autosomal dominant pattern of inheritance presenting with the classical clinical triad of mental retardation, seizures, and adenoma sebaceum (although only 30% present with all three features).

The disease is characterized by hamartomatous tumors and malformations affecting multiple organ systems, the CNS being the most commonly involved, with seizure being the most frequent presenting clinical sign of the disorder. Other than the CNS manifestations, patients may present with renal angiomyolipomas, cardiac rhabdomyomas, and cystic lung disease indistinguishable from lymphangiomyomatosis.

Hamartomatous brain lesions include cortical tubers, white matter heterotopias, subependymal nodules, and the subependymal giant cell astrocytoma. Histologically, cortical tubers, white matter lesions, and subependymal nodules are identical lesions composed of disordered neurons, glia, and giant cells mostly of the astrocyte type, only differing in size and location. Subependymal nodules are usually easily identified with CT due to frequent calcification (>90%) and usually do not enhance thus helping to distinguish, but not entirely exclude a SEGA from a subependymal nodule. Cortical tubers are less likely to calcify and appear as low attenuation lesions at CT, demonstrate increased signal intensity on T2-W images, and rarely enhance. White matter lesions are seen as curvilinear or straight bands of increased T2 signal extending from the ventricles. SEGAs are characterized by slow growth and a benign biological behavior (WHO grade I), likely arising from the degeneration of subependymal nodules. On CT, SEGAs are iso-to slightly hypoattenuating intraventriuclar masses located near the foramen of Monro, with calcification and secondary hydrocephalus being common findings. On MR imaging, SEGAs exhibit hypointense signal compared to white matter on T1-weighted images, heterogenous hyperintensity on T2-weighted images, with intense homogenous enhancement (except for calcified areas). Because MR enhancement cannot always reliably distinguish between subependymal nodules and a SEGA, larger size (>1cm) and interval growth of a mass on annual follow-up CT or MR are considered better indicators of a SEGA rather than a benign subependymal nodule. Therefore, annual surveillance MR imaging is recommended in patients with tuberous sclerosis.

Multiple post traumatic pseudomeningoceles secondary to brachial plexus avulsion with atrophy and myelomalacia of the spinal cord

Findings

Right-sided cyst-like structures are demonstrated at C7-T3. At T1-T2 and T2-T3 these coalesce to form a larger cystic structure overlying the right lung apex.
Additional history: Young adult with history of traumatic brachial plexus injury 2 years ago, now with new onset weakness.

These findings are compatible with the patient's history of previous traumatic right brachial plexus nerve root injury. Since the prior examination, these "pseudomeningoceles" have significantly increased in size. There is a focal 1.5 cm atrophy of the spinal cord with a 6 mm in length area of increased T2 signal is demonstrated within the spinal cord at T1-T2 level consistent with myelomalacia likely the result of the patient's previous nerve root injury.


Diagnosis: Multiple post traumatic pseudomeningoceles secondary to brachial plexus avulsion with atrophy and myelomalacia of the spinal cord


Key points

Cervical nerve root avulsions are the result of traction injuries of the upper extremities that tear the roots from the spinal cord. The roots are absent on the ipsilateral side and the spinal cord is pulled towards the contralateral side.
Pseudomeningoceles are associated with this type of injury. They result from tears in the arachnoid or dura and can easily be identified by MR or CT myelography.
They can be asymptomatic, or present in an acute or delayed fashion with symptoms of myelopathy.
A very rare complication is development of spinal cord herniation.

Ruptured intracranial dermoid

Findings

Fat density lesion within the pericavernous region in the region of Meckel’s cave extending inferiorly into the posterior fossa. Scattered lipid droplets throughout the subarachnoid space.

Differential diagnosis:
- Dermoid cyst
- Epidermoid cyst
- Craniopharyngioma
- Teratoma
- Lipoma


Diagnosis: Ruptured intracranial dermoid


Key points

Congenital inclusion cyst.
Epidemiology: Rare; <0.5% of primary intracranial tumors.
30-50 y/o.
Presentation (uncomplicated): HA (32%), Seizure (30%), rarely with DI, hypopituitarism, visual defects.
Benign, slow growing.
Rare malignant transformation into SCCa.
Increased risk of rupture with increased size.
Significant M&M with rupture: chemical meningitis, seizures, coma, vasospasm, etc.
Fat density distinguishes from epidermoid (usually CSF density).
Scattered lipid droplets in subarachnoid/ventricles with rupture.
20 % have capsular calcium.
Most supratentorial, midline or near midline.
Other sites: spine, orbit.

Spinal foreign body granuloma

Findings

The T2 sagittal and axial images (Figure 2 and Figure 3) show a posterior intradural nodule with low signal intensity which is compressing the spinal cord anteriorly causing cord edema. The sagittal T1 (Figure 1) sequence shows that the nodule is isointense to hypointense which is non specific. It also confirms its extramedullary location.
The axial T1 postcontrast (Figure 4) sequence shows peripheral contrast enhancement with a central hypointense non enhancing area. This could be associated with the presence of central calcification, metal within an inflammatory nodule or the non enhancing central “dot” described in some nerve sheath tumors.


Diagnosis: Spinal Foreign body granuloma


Intradural extramedullary lesions include meningiomas, nerve sheath tumors (schwannomas and neurofibromas), drop metastasis and foreign body granulomas. Meningiomas are globular lesions. They are more common in elderly females. They are usually located in the thoracic region. These tumors are isointense to slightly hypointense on T1. They enhance and can have a dural tail. On T2 they are isointense to hyperintense and can demonstrate low signal on T2 related to intalesional calcification. Meningiomas originate from the denticulate ligament.

Nerve sheath tumors are usually isointense on T1 and hyperintense on T2. They also enhance and can show a central non enhancing “dot”. Hemorrhage and cystic degeneration has been associated with nerve sheath tumors more than with meningiomas. They are slow growing and can erode the bone. Nerve sheath tumors are associated with neurofibromatosis 1 and 2.

Intradural extramedullary metastasis could be the result of drop lesions from primary brain neoplasms such as medulloblastomas or ependymomas or the result of hematogenous spread from solid organ tumors.

Foreign body granulomas are associated with the presence of intrathecal drug delivery pumps more commonly with the administration of opioid derivates or in patients who received agents that were not labeled for long-term intrathecal use. Implanted delivery systems for intrathecal drug administration have become more commonplace in the management of refractory cancer and non-malignant pain. Complications may be related to drug side effects or to technical problems possibly involving the pump and/or catheter

Clues to the diagnosis include the above imaging findings along with the loss of analgesic drug effects accompanied by new, gradually progressive neurological signs and symptoms. Surgery is not always necessary for treatment. Successful resolution has been reported with lower doses and/or changes in the medication delivered.