Oxymorons in medical imaging flip-flops, longitudinally-transverse

In this issue of the journal, Koshy et al.[1] have reported a 23-year-old HIV positive young man with longitudinally extensive transverse myelitis (LETM). They have, in their case snippet, described two magnetic resonance imaging (MRI) appearances of neurosyphilis - (i) flip-flop; and, (ii) candle guttering - with riders to their application.

Even as the epitaph of syphilis was being raised; it has witnessed a resurgence attributed to the AIDS pandemic. Craniospinal involvement in AIDS occurs in tertiary syphilis, in the cord, and its clinical presentation can be acute, sub-acute, or chronic. It is seen as a variably long segment of altered cord signal in T2 studies, akin to other myelopathies. A post-contrast MRI reveals enhancements in the T2 dark areas, explaining the flip-flop.[2] Superficial cord enhancement, often nodular, is referred to as the candle guttering sign.[2] While these signs are helpful, they are neither sensitive nor specific.

MRI is the bulwark of imaging in myelopathy, showing signal changes with a high degree of sensitivity and being robust in the differentiation of compressive and non-compressive pathologies. Signal changes are predominantly T2 prolongation with more subtle T1 shortening and are related to cord edema with or without ischemia. When cord changes extend over 3 or more spinal segments, they are termed LETM; otherwise, the affection is short-segmented. Diffusion aids in detecting acute ischemia and rare cases of cord abscesses. Gradient echo studies may detect hemosiderin in hemorrhagic myelopathy with cord calcifications being rare.

Further elucidation of the etiology of altered cord signals is less robust. Flowcharts are used to rely on clinical presentation, whether acute (demyelination, ischemia, or infection) or non-acute (tumor, metabolic, neurodegenerative, immune, HIV, and others).[3] In the latter group, the presence of cord expansion suggests a tumor. The addition of post-contrast T1 images after gadolinium-based contrast can further aid in this distinction.

Relatively specific post-contrast MRI features have been described.   Enhancement, which is a linear strip with an owl’s eye on axial images, has been described as anterior spinal artery infarction. Enhancement restricted to the lateral columns is specific to paraneoplastic causes. Spondylotic causes are seen as pancake patterns of enhancement with central sparing. Nodular dorsal subpial enhancement alone, or with central canal enhancement, is seen in sarcoidosis.[4]

The so-called candle guttering resembles the nodular subpial enhancement likely to be due to meningeal enhancement. We have personally seen cases of tuberculous myelitis with similar meningeal enhancement. Therefore, this is a non-specific sign, as the authors correctly point out. In cases of idiopathic transverse myelitis, the presence of cord expansion with bright spotty lesions, with the appearance of enhancement, are early MRI markers for increased risk of relapse.[5]

In the case presented by Koshy et al.,[1] the CSF pleocytosis and elevated protein levels pointed to infective myelitis. While the flip-flop appearance of the cord lesions and candle guttering in post-contrast T1 images could suggest a diagnosis, positive CSF and serology tests for syphilis clinched the diagnosis.

Blindly depending on these oxymorons can lead to yes or no, resulting in clinical runouts. As the authors indicate, proceed with caution!