martedì 23 giugno 2009

Ruptured spinal dermoid with chemical meningitis


Figure 1: Sagittal T1W image of the cervicodorsal spine shows multiple hyperintense foci in the subarachnoid space suggestive of fat deposition from dermoid rupture.
Figure 2 and Figure 3: Sagittal T1W and T2W images reveal a heterogeneous hyperintense mass expanding the lower spinal cord and conus medullaris.
Figure 4 and Figure 4: Axial T1W images demonstrate hyperintense signal within the central canal.
Figure 6 and Figure 7: Axial T1W images of brain show fat droplets, seen as hyperintense foci in the peri-mesencephalic cistern and in the frontal horn of left lateral ventricle.

Differential diagnosis
- Spinal dermoid
- Teratomas
- Lipomas

Differential diagnosis of brain lesions that appear hyperintense on T1W images on brain MRI are as follows:
- Lesions with hemorrhagic components (such as infarct, encephalitis, intraparenchymal hematoma, cortical contusion, diffuse axonal injury, subarachnoid hemorrhage, subdural and epidural hematoma, intraventricular hemorrhage, vascular malformation and aneurysm, and hemorrhagic neoplasm)
- Protein-containing lesions (such as colloid cysts, craniopharyngiomas, Rathke's cleft cysts and atypical epidermoids)
- Lesions with fatty components (such as lipoma, dermoid and lipomatous meningioma)
- Melanin-containing lesions (such as metastasis from melanoma and leptomeningeal melanosis)
- Lesions with calcification or ossification (such as endocrine-metabolic disorder, calcified neoplasm, infection, and dural osteoma)
- Lesions with other mineral accumulation (such as acquired hepatocerebral degeneration and Wilson disease)
- Miscellaneous group (which includes ectopic neurohypophysis, chronic stages of multiple sclerosis and neurofibromatosis type I)

Diagnosis: Ruptured spinal dermoid with chemical meningitis

A spinal dermoid is a rare, benign, slow-growing, dysontogenetic tumor arising from the inclusion of ectopic embryonic rests of the ectoderm and mesoderm within the spinal canal at the time of neural tube closure between the 3rd and the 5th week of fetal life. Several causes including spontaneous, iatrogenic or traumatic rupture have been reported to result in dissemination of lipid material from the dermoid tumours into the subarachnoid space or ventricles. Intra-spinal dermoids account for approximately 1–2% of intra-spinal tumors and tend to extend to the subarchnoid space, however there is no communication between the cyst and the subarchnoid space. They occur predominantly in the lumbosacral region and rarely in the cervicothoracic region. They show a slight male predominance, and most reveal themselves during the second and third decades.

Pathologically, spinal dermoids have a thick wall covered with stratified squamous epithelium containing dermal appendages such as hair, sebaceous glands and sweat glands and less commonly, teeth and nails. Dermoid tumours commonly have areas of calcification. Their rupture and spread is a rare event, which may be asymptomatic or may present acutely as chemical meningitis. The exact incidence of rupture of spinal dermoids is not known. Cholesterol, which is the most irritating element of the dermoid excites an inflammatory/ granulomatous meningeal reaction.

Spinal dermoids appear as variegated, space-occupying lesions showing a heterogeneous signal on T2-weighted MRI due to the different components within the cyst. These have high protein-containing fluid and thereby appear brighter than CSF on T1-weighted images. The high lipid content also gives a characteristic hyperintense signal on T1-weighted spin-echo images.

In conclusion, radiologists need to be aware that whenever a diagnosis of intra-spinal dermoid is suggested, it is essential to screen the entire neural axis to look for possible rupture and CSF spread. MRI is the imaging modality of choice.

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