venerdì 28 aprile 2006
There is osseous obliteration of the visualized cochlea (Figure 1), vestibule, and lateral semi-circular canal (Figure 2).
Diagnosis: Labyrinthitis ossificans
The most common causative factor is inflammation of the inner ear, secondary to bacterial meningitis and subsequent purulent labyrinthitis. Other, less common causes include labyrinthectomy, temporal bone trauma, autoimmune inner ear disease, sequela of mumps or measles, and otitis media with associated suppurative labyrinthitis.
Ossification in labyrinthitis ossificans commonly occurs primarily at the basal turn of the cochlea, which is the insertion site of the electrodes of cochlear implant devices, and subsequently may interfere with full insertion and successful results. MRI is used to assess for early fibrosis prior to the formation of calcification.
mercoledì 26 aprile 2006
Figure 1 and Figure 2: T2 and gradient echo hypointensity is demonstrated along the pial surfaces of the brain, and subarachnoid 7th and 8th cranial nerves. The hypointensity seen on the gradient echo images is more prominent than that on the T2/FLAIR sequences, consistent with blooming due to hemosiderin deposition.
Figures 3, Figure 4, and Figure 5: T2 and gradient echo hypointensity is demonstrated along the pial surfaces of the brain, spinal cord, and the subarachnoid courses of the visualized nerve roots. As in Figure 1 and Figure 2, the hypointensity seen on the gradient echo images is more prominent than that on the T2/FLAIR sequences, consistent with blooming due to hemosiderin deposition.
Diagnosis: Superficial siderosis
Superficial siderosis (SS) of the central nervous system is the sequela of chronic recurrent subarachnoid hemorrhage. Hemosiderin, a blood product of chronic hemorrhage, is deposited along the leptomeningeal surfaces of the brain and spinal cord, as well as the subarachnoid surfaces of the cranial and spinal nerves. The hemosiderin deposition is not benign. The leptomeninges become thickened and the affected nervous tissue can undergo neuronal loss, reactive gliosis, and demyelination. Classic locations for hemosiderin deposition in SS are the peripheral folia of the cerebellum. Hemosiderin deposited here is usually associated with Bergmann gliosis and death of Purkinje cells. This leads to cerebellar atrophy, especially involving the vermis.
The cranial nerves are often affected with preferential involvement of cranial nerves VIII and I. These nerves seem to be more frequently affected due to their relatively long courses through the subarachnoid space. As the hemosiderin can be neurotoxic, patients with SS can present with sensorineural hearing loss and anosmia. Symptomatic involvement of cranial nerves V and VII also occur with some frequency. SS is associated with hydrocephalus, as the subarachnoid granulations become impaired from the chronic subarachnoid hemorrhage.
The MR findings of SS are characteristic. Pial T2 and gradient echo (GRE) hypointensity is demonstrated along the leptomeningeal surfaces of the brain and spinal cord. The pons and cerebellum are two of the most frequently affected regions. T2 and GRE imaging also show hypointensity along the subarachnoid portions of the cranial and spinal nerves. The hypointensity demonstrated on the T2 “blooms” on GRE imaging due to hemosiderin MRI susceptibility.
The etiology of SS includes trauma, vascular anomalies, and neoplasm. Any process producing subarachnoid hemorrhage can result in SS. Between 80% and 90% of nontraumatic subarachnoid hemorrhage is the result of intracranial aneurysm rupture. Other vascular malformations that have significant frequencies of hemorrhage are AVMs and cavernous angiomas. Diagnosis of SS mandates an evaluation for the source of the hemorrhage and should include both intracranial MRI/MRA, as well as total spine MRI. Traditional cerebral - spinal angiography may be necessary to identify subtle vascular abnormalities. The etiology of SS is not identified in 25% to 46% of patients.
venerdì 21 aprile 2006
Noncontrast enhanced CT of the brain reveals multiple high-density brain lesions with surrounding vasogenic edema, suggestive of hemorrhagic metastases (Figure 1 and Figure 2). Post-contrast images demonstrate enhancement of several of the lesions (Figure 3 and Figure 4).
Medialstinal and lung windows from the CT of the chest (not shown)demonstrated the primary lung carcinoma.
Diagnosis: Multiple hemorrhagic intracranial metastases from primary lung carcinoma
Metastatic spread to the brain is usually arterial, although less commonly spread via the Batson venous (pelvic, GI tumors) may occur. Most metastatic lesions are well-demarcated and tend to cluster at the gray-white matter junction.
Most of the brain metastases originate either from a primary lung tumor or from metastatic lesions in the lungs, since most large aggregates of tumor cells are filtered by the lung capillary network. Single tumor cells, however, can pass through the lung capillary network, and larger tumor emboli can pass from the venous to arterial circulation through a patent foramen ovale or a right to left shift.
The most likely malignancies to produce hemorrhagic metastases are melanoma, renal cell carcinoma, choriocarcinoma, thyroid, lung, breast, and germ cell tumors. Due to their increased prevalence, however, bronchogenic lesions are the most common source of hemorrhagic lesions.
Up to 20% of patients with metastases to the brain present with seizures.
Mnemonic MR CT BB
R: Renal cell carcinoma
T: Thyroid, terratoma
B: Bronchogenic carcinoma
B: Breast carcinoma
giovedì 13 aprile 2006
Figure 1: Reconstructed sagittal CT scan through the thoracic spine demonstrates a flattened vertebral body. The disk spaces are maintained. The remaining vertebral bodies are unremarkable.
Figure 2: Sagittal T2-weighted MRI demonstrates a focal kyphosis at the level of the flattened vertebral body, with a ventral epidural soft tissue component resulting in thoracic spinal cord compression.
Figure 3: Sagittal T1 post-contrast MRI with fat saturation again demonstrates a focal kyphosis at the level of the flattened vertebral body. The ventral epidural soft tissue component is better demonstrated than on the T2 series
Differential diagnosis for vertebral plana = “MELTS”
- M: Metastasis, myeloma
- E: Ewing’s sarcoma
- L: Langerhan’s cell histiocystosis, leukemia, lymphoma
- T: Trauma, tuberculous osteomyelitis
- S: Steroids
Diagnosis: Vertebral plana due to Langerhan's cell histiocystosis
LCH predominantly affects children and is comprised of three conditions: eosinophilic granuloma, Hand-Schuller-Christian disease, and Letterer-Siwe disease. All three conditions are characterized by the presence of abnormal histiocytes called Langerhan’s cells. Eosinophilic granuloma is the mildest form and is the most common, comprising approximately 70% of the disease. It consists of single or multiple bony lytic lesions, and most commonly involves the skull, mandible, spine, ribs, and long bones. Hand-Schuller-Christian disease (20% of LCH) is a multisystem disease comprised of diabetes insipidus, exopthalmos, and one or multiple bony lesions. It is fatal in approximately 30% of patients. Letterer-Siwe disease (10% of LCH) is the most severe form and it affects children less than three years old with liver, spleen, skin, and bony involvement. It is usually fatal within two years of diagnosis.
Eosinophilic granuloma is a benign condition that has a variable prognosis. Specifically, the prognosis for vertebral plana is favorable. The lesions may regress spontaneously, taking up to two years. The treatment is often conservative, but surgery, radiation, chemotherapy, and steroids may be used if conservative treatment fails.
martedì 11 aprile 2006
A cystic lesion (2.0 x 1.8 x 1.2 cm) with thin and well-defined enhancing walls (Figure 1 and Figure 2) places mild mass-effect on the tectum. No hydrocephalus is present. The cystic lesion (Figure 1, Figure 2, Figure 3 and Figure 4) is homogeneously isointense to CSF on T1-weighted imaging, uniformly hyperintense on FLAIR sequences, and isointense to CSF on T2-weighted imaging. No diffusion restriction is seen on diffusion-weighted imaging. These findings are most compatible with a pineal cyst. Less likely, this may represent a pinecytoma.
- Pineal cyst
- Normal pineal
- Epidermoid cyst
- Arachnoid cyst
- Germ cell neoplasm
Diagnosis: Pineal cyst
Pineal cysts are usually asymptomatic and are often discovered incidentally. They have been discovered in up to 40% of patients on autopsy studies. Patients with large pineal cysts may experience headaches secondary to obstructive hydrocephalus. Rarely, pineal cysts can produce Parinaud syndrome (paralysis of upward gaze, lid retraction, and abnormal pupillary movements). If the cyst is hemorrhagic, acute hydrocephalus can develop. Young females (aged 21-30) are affected more than males (female to male ratio is 3:1). The cysts commonly enlarge with puberty and then regress with age.
On CT, the pineal cyst contents are usually isodense relative to CSF. The wall may be calcified. The cyst wall (nodular or thin) may enhance with contrast. Pineal cysts have a variable appearance with MR. Cystic contents are most often hyperintense relative to CSF, but may be isointense on T1-weighted imaging. On T2-weighted sequences, the cystic contents are either isointense or hypointense to CSF. On FLAIR sequences, the cystic contents are hyperintense. No restriction is seen with diffusion-weighted imaging. The cyst walls may enhance (60%). On delayed images, the cystic contents may enhance.
The key management issue regarding a pineal cyst, is the fact that they can be indistinguishable from a pinecytoma. Therefore, a histological diagnosis may be needed to make the distinction. If biopsy or surgery is not performed, long-term follow-up imaging should be obtained. Some suggest that clinical follow-up without imaging is an acceptable alternative. In one follow-up series, the cysts did not change in size in 75% of patients.
martedì 4 aprile 2006
Contrast-enhanced CT examination of the neck demonstrates an ovoid, well-circumscribed low attenuation lesion in the right neck.
The images show a branchial cleft cyst, which is well-circumscribed with a thin enhancing rim. The branchial cleft cyst is anteromedial to the sternocleidomastoid muscle (Figure 1 and Figure 2) and lateral to right internal and external carotid arteries (Figure 1 and Figure 2).
Differential for a cystic neck mass in the adult:
- Thyroglossal duct cyst
- Thymic cyst
- Suppurative lymph node
- External laryngocoele
- Necrotic squamous cell carcinoma
Diagnosis: Branchial cleft cyst
During normal embryologic development, the branchial arches arise at four weeks. The second branchial arch overgrows the third and fourth arches during development.
The branchial arches involute by week seven. If an arch fails to involute completely, it may form an epithelial-lined cyst. These congenital cysts may be identified in the early years with a second peak incidence in the second and third decades. BCCs are typically a painless compressible mass. They may occasionally become infected and present with fever, induration, and tenderness.
The second BCC is the most common, accounting for 90% of BCCs. A second BCC is typically found at or slightly below the angle of the mandible. The second BCC is centered lateral to the carotid sheath and anteromedial to the sternocleidomastoid muscle. Medial beaking of the cyst can be seen if it extends between the external and internal carotid arteries. The less common first BCC is seen in a periauricular or periparotid location. It can communicate with the external auditory canal and can be associated with otorrhea and parotid gland cysts. A third BCC is seen in the posterior cervical space.