CNS fungal aspergillosis

Findings

T2 weighted intraparenchymal masses in the right temporal lobe and in the right superior frontal gyrus extending across the corpus callosum. There is ependymal enhancement of the right lateral ventricle. There is very minimal enhancement of the masses.

Differential diagnosis:
- CNS leukemia
- CNS aspergillosis
- CNS bacterial infection
- Metastasis
- Septic emboli


Diagnosis: CNS fungal aspergillosis


Key points

Aspergillosis is the 2nd most common fungal CNS infection in an immunocompromised host after cryptococcus.

Risk factors:
- Transplant recipients: renal >liver > heart.
- 1-4 months post transplant.
- Recent transplant rejection +/- retransplantation.
- Leukopenia.
- Associated with CMV infection.
- Reported nosocomial spread in some cases.
- Lung is commonest source then sinuses.


Imaging

Best finding: Multiple lesions with infarction or hemorrhage in a random distribution due to the angioinvasive nature of the infection. Hemorrhage occurs in approximately 25% of lesions.
Low signal intensity is often seen in the periphery of the lesions on T2-weighted MR images. This finding corresponds at least partially to areas of hemorrhage.
Multiple ring enhancing lesions, although more commonly there is mild/vague enhancement.
Dural enhancement with enhancement in adjacent paranasal sinus.
Mycotic aneurysms may be seen on angiography.
Locations of involvement a felt to be secondary to predilection for the lenticulostriate and thalamoperforator vessels: basal ganglia and thalamus, corpus callosum. The corpus callosum is involved in relatively few other processes (e.g., high-grade astrocytoma, cerebral lymphoma, multiple sclerosis, and Marchiafava-Bignami disease). Metastasis and pyogenic abscess do not commonly involve the corpus callosum.

Differential diagnosis in the immunocompromised patient includes
- Lymphoma
- Metastatic disease
- Septic emboli
- Multiple infarcts

Lack of enhancement may suggest the diagnosis of aspergillosis, since most brain tumors enhance. A prospective diagnosis should be suggested in the setting of early infarction and hemorrhage in the brain of an immunocompromised patient, so that antifungal therapy may be instituted.
Definitive diagnosis obtained with biopsy. Neuropathology shows invasion of blood vessels causing hemorrhagic infarction usually subcortical Meningeal infection usually focal & adjacent to infected cerebral region Angular dichotomously branching septate hyphae infiltrates tissue in centrifugal pattern. Hyphae structure tend to be found on borders of large abscesses.


Prognosis is poor with approximately 35% complete or partial response, although improved from previously 90% mortality. Treatment with Amphotericin B iv (liposomal form avoids nephrotoxicity) +/- 5 fluorocytosine often combined with itraconazole.

Reflex sympathetic dystrophy (RSD)

Findings

Three phase technetium 99m labeled MDP bone scan is shown. There is abnormal radiopharmaceutical uptake in the periarticular regions of the left hand and wrist on both immediate and delayed images.

Differential diagnosis:
- Reflex sympathetic dystrophy
- Inflammatory arthritis


Diagnosis: Reflex sympathetic dystrophy (RSD)


Key points

RSD is a poorly understood chronic abnormality of the sympathetic nervous system in a regional distribution (usually the distal extremities) that follows trauma, surgery, infection, casting, or splinting.
Clinically, it presents as severe, protracted pain in the affected limb that is out of proportion to the original injury. Additionally, there may be vasomotor disturbances. Progresses to skin and muscular atrophy.
Synonyms: Sudeck's atrophy, Complex regional pain syndrome type 1, Causalgia.

Three phases have been described:
1) Non focal pain with decreased range of motion, soft tissue edema, and increased skin temperature (lasts weeks to months)
2) Decreasing pain and skin temperature with skin thickening. Atrophy and osteoporosis may become apparent (lasts 3-6 months)
3) Continued pain with increasing atrophy and joint stiffness. Contractures may occur.

May occur in up to 5% of all injuries; most often in the upper extremity.
Typically, affects females more, often less than 50 years of age.
Plain radiographs only 60% sensitive and non-specific, showing osteoporosis of the affected limb with associated soft tissue swelling or atrophy (depending on the stage).
CT also insensitive and non-specific.
MR may show patchy bone marrow edema with stage dependent soft tissue changes.
Nuclear medicine three phase bone scan is the best study for diagnosis of RSD, showing diffuse increased uptake in the affected region on flow images; continued diffuse uptake on blood pool images, beginning to localize to periarticular regions; and continued uptake in the periarticular regions on delayed images.
Delayed images are the best for diagnosis, with a reported sensitivity of near 100%.
A "reversed" pattern of decreased relative uptake in the affected extremity may be seen on bone scan, however. This is most common, but not exclusively, in pediatric patients.
Treatment: medications (steroids, opiates, anti-epileptics, etc.); physical therapy; sympathetic nerve block; surgical sympathectomy.

Gas producing otogenic brain abscess with cerebral edema and pseudosubarachnoid hemorrhage sign

Findings

Figure 1: Soft tissue windows demonstrate generalized cerebral edema with loss of grey-white differentiation and near total obliteration of the CSF spaces. An ill-defined hypodense gas containing region is present within the left temporal lobe consistent with abscess formation. The subarachnoid spaces are hyperdense especially in the suprasellar region representing pseudosubarchnoid hemorrhage associated with cerebral edema and/or pyogenic leptomeningitis, not true hemorrhage.
Figure 2: Nondependently layering air is present within the anterior horn of the left lateral ventricle indicating communication between the left temporal lobe abscess and the left lateral ventricle and CSF spaces. On soft tissue windows, normal subcutaneous fat is seen confirming that this is intraventricular air, not fat.
Figure 3 and Figure 4: Bone windows demonstrate total opacification of the middle ear cavity and mastoid air cells consistent with otitis media and mastoiditis. There is subtle bony sclerosis and remodeling which along with the patient’s history is consistent with chronic otitis media with mastoiditis. Also note that there is no evidence of fracture to suggest penetrating trauma as an etiology for these findings. Bone window confirms the presence of air, not fat, in the frontal horn of the right lateral ventricle.


Diagnosis: Gas producing otogenic brain abscess with cerebral edema and pseudosubarachnoid hemorrhage sign


Complications of chronic supurative otitis media include (in order of decreasing frequency):
- mastoid abscess
- meningitis
- postauricular fistula
- lateral dural venous sinus thrombosis
- facial palsy
- cerebellar abscess
- Bezold’s abscess (involving sternocleidomastoid muscle)
- internal jugular vein thrombosis
- epidural abscess
- perisinus abscess
- Gradenigo’s syndrome (due to petrous apicitis)
- interhemispheric abscess
- temporal lobe abscess
- subdural abscess
- serous labyrinthitis
- Luc’s abscess (subperiosteal temporal bone without mastoiditis)

Otitic meningitis is the most common intracranial complication and can occur as a result of direct disease extension from the mastoid through a cortical defect or due to retrograde thrombophlebitis despite an intact appearance of the bone. Otogenic brain abscesses usually occur in the temporal lobe and cerebellum (2:1). Nearly all otogenic brain abscesses have underlying chronic suppurative otorrhea. More than half of all otogenic brain abscesses have an associated cholesteatoma.

Although the relative incidence of complications related to chronic otitis media is debated within the literature, many authors agree that the most dangerous complication is intracranial abscess formation which carries a 40-50% mortality rate. According to Nunez et al, 1.5 % of adults have active chronic otitis media and in an adult with active chronic otitis media, the annual risk of developing an intracranial abscess is about 1:10,000 with a male to female risk ratio of approximately 3:1. Though at first glance this risk appears relatively low, the lifetime expectancy of a 30 year old person with active chronic otitis media developing an abscess is 1:200. Intracranial complications in patients with active chronic otitis media are also more prevalent in adolescents and young adults.

Radiologic evaluation of a patient suspected of having intracranial complications related to active chronic otitis media is crucial to diagnosis and management. Axial CT with contrast is the usual modality of choice preferably with thin cuts, which can demonstrate the presence or absence of an abscess as well as details regarding its size and location. An intraparenchymal mass may show parenchymal low density with mass effect with or without an enhancing capsule. CT may be limited in the setting of acute infections. MRI may improve diagnostic accuracy, with increased sensitivity and specificity.

Etiologic agents usually include anaerobes, Proteus mirabilis, Pseudomonas aeruginosa, Streptococcus, and Staphylococcus. Anaerobic and gram negative bacteria appear to be the most common causes. Consequently, in addition to surgical management, initial treatment should include broad spectrum antibiotics with good cerebrospinal fluid penetration as well as anaerobic coverage. A team approach including an otolaryngologist, radiologist, anesthesiologist, and an infectious disease specialist among others is recommended for optimal outcome.


Pseudosubarachnoid Hemorrhage Sign

A pseudosubarachnoid hemorrhage sign is an unusual neuroradiologic finding which may be present in cases of diffuse cerebral edema and/or pyogenic leptomeningitis. In addition to increased attenuation of the otherwise normal subarachnoid spaces, the falx and tentorium can also appear dense. The etiology of this presentation is unknown. Current theories include: 1) blood-brain-barrier breakdown from microorganism toxins in pyogenic meningitis allowing leakage of dense proteinaceous material into the subarachnoid spaces; 2) cerebral edema causes displacement of CSF from the subarachnoid spaces with engorgement of the superficial pial structures creating a predominantly vascular space with relatively dense intravascular blood. Since management of the causes of subarachnoid and pseudosubarachnoid hemorrhage is quite different, it is important to be able to recognize this relatively rare sentinel neuroradiologic sign.

Retinoblastoma

Findings

Large calcified mass in the left lobe optic globe posteriorly in contact with the optic nerve. Left optic globe size near symmetric with the right.

Differential diagnosis:
- Retinoblastoma
- Persistent hyperplastic primary vitreous
- Coat's disease
- Toxocara infection
- Phthisis bulbi


Diagnosis: Retinoblastoma


Discussion

Retinoblastoma arises from a cell of neuroepithelial origin, usually in the posterior retina. It is the most common malignant eye tumor of childhood and is responsible for 1% of all deaths from cancer in the age group of newborns to 15 years. Retinoblastoma can be multifocal and bilateral (30%); it undergoes spontaneous regression more frequently than other tumors; has a high incidence of second primary tumors; and occurs as a congenital tumor.

Retinoblastoma affects all racial groups. It occurs in approximately 1:15,000 to 1:34,000 live births. The majority of cases are diagnosed before the age of four and the incidence declines with age. It affects males and females with equal frequency.

Retinoblastoma occurs in both familial (40%) and sporadic (60%) patterns. Familial cases typically develop multiple and bilateral tumors, although they may be unifocal and unilateral. Sporadic cases are always unilateral and unifocal.

Retinoblastoma serves as prototype for a group of cancers caused by recessive loss of suppressor cancer genes. These include osteosarcoma, Wilm's tumor, hepatoblastoma, rhabdomyosarcoma, uveal melanoma, bladder cell carcinoma, acoustic neuroma, and meningioma. Retinoblastoma and osteosarcoma arise after the loss of the same genetic locus (13q14 band).

Tumor cells may disseminate through the choroidal vasculature or may spread beyond the eye through the optic nerve or subarachnoid space. In advance cases, the tumor may penetrate through the sclera and grow in the orbit. Metastases to the preauricular and cervical lymph nodes commonly follow over extraocular extension. The most common sites of distant metastases are the CNS, skull, distant bones, and lymph nodes. Spontaneous regression occurs in 1% of cases.


Diagnosis

The diagnosis is usually made before age 2 when a white reflex from the pupil ("cat's eye") or leukokoria, strabismus, or eye pain is investigated. Ophthalmoscopy and CT scans are helpful.


Therapy

If diagnosed when the tumor is intraocular, >90% can be cured. Enucleation and removal of as much optic nerve as possible usually manage unilateral cases. In asymmetric bilateral cases, the more involved eye is enucleated and the other eye is treated by photocoagulation, cryotherapy, radiation, and systemic antimetabolites- often in combination. Spinal fluid and bone marrow aspirated should be examined for metastases. Family members should be examined.


Radiology

CT demonstrates a solid retrolental hyperdense mass with associated retinal detachment. Associated findings include extraocular extension, optic nerve enlargement, and partial or complete calcification. Calcification is commonly seen and is a good prognostic indicator; contrast enhancement is a poor prognostic indicator.

Intralabyrinthine hemorrhage

Findings

Axial T1 fat-saturated MRI of the internal auditory canal (precontrast) shows acute hemorrhage with hyperintensity in the cochlea and vestibule.


Diagnosis: Intralabyrinthine hemorrhage


Sudden hearing loss secondary to an acute cochlear hemorrhage is rare. Estimates of annual incidence of sudden hearing loss are 5-20 per 100,000 of which only a small percentage is due to intralabyrinthine hemorrhage. Only 1-4% of all cases of sudden sensorineural hearing loss are bilateral. The fact that this patient has Down syndrome is significant, since hearing loss has been reported in both acute and chronic myeloid leukemias, which occurs at a higher frequency in Down patients. One theory proposes that hyperleukocytosis causes leukostasis with abnormal microvascular perfusion. The cochlea is an end organ in terms of its blood supply with no collaterals. It is supplied by the labyrinthine artery, a branch of AICA. Its tortuous course predisposes it to the effects of hyperviscocity. In addition, it is extremely sensitive to changes in blood supply. Thus, the time course of hearing loss correlates well with a vascular event such that an acute hearing loss is most likely caused by hemorrhage, thrombosis, embolism or hypotension. This patient should be evaluated for an underlying leukemia.

Imaging can be used as an adjunct in both conductive and sensorineural hearing loss. CT imaging is more sensitive for conductive hearing loss while MR is more sensitive for sensorineural hearing loss. Fluid in the labyrinth is normally isointense with CSF. In the acute phase of hemorrhage, hypointense signal can be seen on T2-weighted images, while hyperintense T1 signal can be seen for up to 6 months because of the extended life span of the erythrocytes in the perilymph. Other possible causes of sensorineural hearing loss that can be seen on MR include vestibular schwannomas, arachnoid cysts, multiple sclerosis, and inflammation.

Mandibulofacial dysostosis (Treacher-Collins syndrome)

Findings

The lateral plain radiograph of the skull demonstrates the typical facial features of the abnormality. There is marked bowing of lower border of the mandible. The mastoids are acellular with absent external auditory canals. Note the constriction of the air-outlined pharynx, particularly at the level of the oropharynx. There is aplasia of the zygomatic arches.
Axial CT images through the level of the ear structures demonstrate microtia and aplasia of the external auditory canals. Congenitally small and abnormal middle ear cavities with absent ossicles. There is thickening of the bone at the oval window and dehiscence of the bilateral posterior semicircular canals.

Differential diagnosis:
- Maxillofacial dysostosis
- Mandibulofacial dysostosis (Treacher-Collins syndrome)
- Nager syndrome
- Oculoauriculovertebral sequence
- Toriello type mandibulofacial dysostosis


Diagnosis: Mandibulofacial dysostosis (Treacher-Collins syndrome)


Key points

Mode of inheritance: Autosomal dominant; genetic homogeneity; almost complete penetrance and wide variability in expression.
Gene maps to chromosome 5q32-33.1.
Prevalence of Treacher Collins syndrome is in the range 1 per 25,000 to 1 in 50,000 live births.


Clinical manifestations

Abnormalities in the structures derived from the first and second pharyngeal pouch, groove, and arch.
Facial hypoplasia with sunken cheek bones and malformed ears.
Macrostomia.
Cleft palate and or cleft lip with palatopharyngeal incompetence.
Obliteration of the nasal frontal angle with narrow nares and hypoplasia of the alar cartilages.
Down slanting of the palpebral fissure and coloboma in the outer portion of the lower lid.
Conductive deafness.
Dental anomalies.
Projection of scalp hair onto the lateral aspect of the cheek.
Some association with congenital heart disease, TEF, and anal atresia.


Radiologic manifestations

Hypoplasia of the malar bones.
Concave curvature of the horizontal ramus of the mandible is pathognomonic.
+ Hypoplasia or aplasia of the condylar and coronoid processes of the mandible.
Underdeveloped paranasal sinuses.
Various ear anomalies.
+ Hypoplasia or aplasia of the EAC.
+ Hypoplasia or aplasia of the tympanic cavity.
+ Closed middle ear cavity by a thick, osseous atretic plate.
+ Closed oval window.
Hypoplasia or aplasia of the mastoid air cells.
Progressive cranial basilar kyphosis associated with narrowing of the anteroposterior pharyngeal diameter and pharyngeal hypoplasia.
Vertebral anomalies.

Spinal pilocytic astrocytoma

Findings

There is an intramedullary, heterogeneously enhancing mass expanding the spinal cord from the level of C2 to C7-T1. The mass has iso to hypo intense T1 signal with areas of hyper intense T2 signal. There is an associated cystic portion of edema up to the pons in the brainstem (as shown on initial axial image). There is increased T2 signal within the spinal cord that extends inferiorly from the mass to the level of T7.

Differential diagnosis:
- Astrocytoma
- Ependymoma
- Ganglioglioma


Diagnosis: Spinal pilocytic astrocytoma


Key points

Primary spinal cord tumors account for 2 to 4 percent of all primary CNS tumors. One-third are located in the intramedullary compartment and are gliomas.
Astrocytomas are second in prevalence to ependymomas in adults; however, they are the most common intramedullary tumor in children.
Most common site of involvement is the thoracic cord followed by the cervical cord.
Can involve the entire spinal cord in children, but quite rare in adults.
Isolated conus medullaris involvement is seen in about 3% of cases. Rarely in the filum terminale.
Pilocytic astrocytomas are a subset of astrocytomas that are low-grade and well-circumscribed with intense enhancement on MR imaging.
Usually are iso- to hypo intense relative to the spinal cord on T1-weighted images and hyper intense on T2-weighted images.
Average length of involvement is seven vertebral segments.
Cysts are a common feature.
Usually eccentric because they arise from parenchyma and not central canal.

Sphenoid wing dysplasia

Findings

Figure 1: CT head without contrast demonstrates partial protrusion of the left temporal lobe and associated dura and CSF through the bony defect producing distortion of the optic nerve and proptosis. Also of note is a contusion in the left temporal lobe and left preseptal soft tissue swelling.
Figure 2, Figure 3, Figure 4, Figure 5, and Figure 6: CT head without contrast demonstrates absence of the left sphenoid wing. There is also a left occipital and right petrous bone fracture.
Figure 7 and Figure 8: Anterior and posterior volume rendered 3-D CT images demonstrate a gaping bony defect in the posterior aspect of the left orbit. The normal anatomical landmarks of the optic nerve canal, superior and inferior orbital fissures are not identified, and the anterior clinoid is not present. The margins of the bony defect are smooth and regular suggesting that this is developmental in nature.


Diagnosis: Sphenoid wing dysplasia


Sphenoid wing dysplasia can occur as an isolated finding or in patients who have Neurofibromatosis type 1. Approximately 50% of cases are associated with neurofibromatosis type 1. Sphenoid dysplasia has been reported to occur in 1 to 7% of patients with neurofibromatosis. Sphenoid wing lesions are usually asymptomatic, but patients can present with pulsating exophthalmos or enopthalmos. Others can present with vision impairment, extra-ocular muscle impairment or inflammation of the conjunctiva.

The radiological features of sphenoid wing dysplasia are a defect in a part or all of the greater wing, elevation of the lesser wing and distortion of the sella. There may be elevation of the superior orbital fissure, enlargement of the temporal fossa in all directions and lifting of the sphenoid ridge out of the orbit.

The most likely cause of sphenoid dysplasia is defective ossification of the sphenoid bone. In patients with NF-1, sphenoid wing dysplasia was initially thought to be congenital and non-progressive. It is now believed to be progressive in some patients with NF-1. Sphenoid wing dysplasia is one of six clinical criteria for the diagnosis of NF-1.

Cerebellopontine angle and intravestibular lipomas

Findings

Figure 1: Nonenhanced thin-section T1-weighted axial MR image demonstrates two small lesions in the right cerebellopontine angle and the right vestibule, respectively. Both demonstrate high signal similar to subcutaneous fat.
Figure 2: T2-weighted image also demonstrates high signal in the right cerebellopontine angle lesion and the right vestibule lesion.
Figure 3: FIESTA image demonstrates a dark rim surrounding the CP angle lesion, consistent with chemical shift artifact at the boundary between the lesion and the surrounding CSF.
Figure 4: Post-contrast fat-saturated T1-weighted image shows complete suppression of signal from both lesions, confirming that they are composed of fat.


Diagnosis: Cerebellopontine angle and intravestibular lipomas


Cerebellopontine angle lipomas and vestibular lipomas are rare lesions. Any cerebellopontine angle or vestibular mass can cause a patient to present with sensorineural hearing loss, as in this case. MRI with dedicated thin images through the internal auditory canals is the preferred imaging technique for evaluation of sensorineural hearing loss.

Intracranial lipomas are thought to be congenital lesions. While most are asymptomatic, they can grow over time and cause clinically significant symptomatology. They occur most commonly in the interhemispheric, quadrigeminal/superior cerebellar, and suprasellar/interpeduncular regions, followed by the cerebellopontine angles. Intravestibular lipomas are extremely rare, with only a few cases reported in the literature. However, there is a known association between cerebellopontine angle lipomas and intravestibular lipomas.

In this case, the very high signal in both lesions on the T1-weighted images suggests fat content. Low-signal rims around the lesions on relatively T2-weighted gradient series (such as True FISP or FIESTA) is due to chemical shift at the fat-CSF boundary. Fatty content is definitively confirmed by a fat-saturated T1-weighted sequence.

Sturge-Weber syndrome

Findings

Hyper density on CT in the left tempero-occipital region which may represent calcium and/or hemorrhage, possibly parenchymal and in the subarachnoid space. Non contrast MRI demonstrates FLAIR hyper intensity in the left tempero-occipital region involving cortex and subarachnoid space. Absent mass effect and vasogenic edema. On contrast enhanced MRI, there is enhancement within sulci in this region and mild asymmetric enlargement of the left choroid plexus.

Differential diagnosis:
- Sturge-Weber syndrome
- Subarachnoid hemorrhage
- Infiltrating astrocytoma
- Meningitis


Diagnosis: Sturge-Weber syndrome


Discussion

Sturge-Weber syndrome is sporadic disease known descriptively as encephalotrigeminal angiomatosis. The causative etiology is unknown, but the disease is characterized by angiomata in the distribution of the fifth cranial nerve and in the leptomeninges, most commonly in the parietal and occipital lobes. This focal abnormal development of venous drainage results in vascular congestion, ischemia, atrophy and eventually calcification. "Port-wine" vascular nevus flammeus in the trigeminal nerve distribution (most commonly in V1) is a commonly encountered cutaneous finding. Patients frequently present with seizure in the first year of life. These are usually focal and involve the side of the body contralateral to the nevus. Focal cerebral ischemia may result in dystrophic calcification, seizure (80%), mental retardation (>50%), hemianopsia, and hemiplegia. About one third of patients will have ocular involvement, with buphthalmos and glaucoma.


Radiology

Calcification may be seen on plain film of the skull, and on the CT scanogram. Significant calcium deposition before the age of 2 is uncommon. Tram-tracking is the characteristic finding, resulting from calcification of apposing gyri surrounding a dilated sulcus. CT demonstrates gyriform, curvilinear calcification, most prominent in the parietal and occipital lobes ipsilateral to the facial nevus. Secondary changes in the skull are sometimes present, such as enlargement of the paranasal sinuses and mastoid air cells. Strong post-contrast enhancement may be seen in both the angiomata, as well as the ipsilateral choroid plexus. Prominent collateral drainage through subependymal and medullary veins may be seen, particularly with angiography or MR venography.