Benign Notochordal Cell Tumour (BNCT)

To understand a benign notochordal cell tumour it helps to go back to the very earliest stages of development. Long before the bones of the spine appear, the embryo lays down a flexible rod that runs the length of the future backbone. This rod is the notochord, and it acts as a template around which the vertebrae and the discs between them are built. Once that scaffolding has done its job, the notochord is largely reabsorbed, leaving only the soft, jelly-like centre of each intervertebral disc, the nucleus pulposus, as its lasting remnant.

In a proportion of people, small islands of the original notochordal cells are left behind not in the discs but inside the bone itself, within the vertebral bodies and the bone at the base of the skull. These rests of cells are entirely normal in the sense that they are a common quirk of human development. When such a rest grows large enough to form a visible mass within the bone, it is termed a benign notochordal cell tumour. The same lesion has been described in the older literature under the name giant vertebral notochordal rest, and the two terms refer to essentially the same thing.

The word tumour here simply means a growth or swelling, and it should not be read as implying anything sinister. A benign notochordal cell tumour is, as its name states, benign. It does not spread, it does not invade, and it behaves as a quiet, static collection of cells sitting within the bone.

Benign notochordal cell tumours are far more common than most people would imagine, precisely because they so rarely announce themselves. Their true frequency has been revealed by autopsy studies, in which the spine and skull base of people who died of unrelated causes have been examined microscopically. Such studies have repeatedly found small notochordal lesions in a substantial minority of the population, with figures of up to around one in five reported in some cadaveric series.

Because most of these lesions are tiny, only the larger ones are visible on imaging, and so the proportion picked up on scans during life is much lower than the autopsy figure, reported in one study at well under one per cent of those imaged. This gap between how often the lesions exist and how often they are seen is a recurring theme, and it means that benign notochordal cell tumours are almost certainly under-recognised rather than rare.

The lesions follow the distribution of the original notochord, and so they cluster in particular places. The bone at the base of the skull, the clivus, and the lowest part of the spine, the sacrum and coccyx, are the commonest sites, followed by the bones of the neck and the lower back.

The reassurance that surrounds a benign notochordal cell tumour rests on a small number of consistent features. The first is that it is intraosseous, meaning it lies entirely within the bone. It does not break out through the surface of the vertebra or the clivus, and it does not form a mass in the soft tissues around the bone. The second is that it does not destroy bone. On the contrary, the bone around it often appears slightly denser than normal, a feature described as mild sclerosis. The third is that it has well-defined, well-corticated margins, sitting within the bone like a discrete, contained patch. The fourth, and one of the most useful, is that it does not take up contrast dye on a scan, reflecting its quiet, non-aggressive nature.

Taken together, these features describe a lesion that is contained within bone, leaves the bone intact, has a clean edge and shows no aggressive activity. This combination is what underlies the description of these lesions as benign.

On magnetic resonance imaging, the workhorse of spinal imaging, a benign notochordal cell tumour typically appears as a rounded, well-defined area within the bone. It shows low signal, appearing dark, on the T1-weighted sequence, and high signal, appearing bright, on the T2-weighted sequence. It does not enhance after contrast and shows no restriction on diffusion sequences. Importantly, there is no breach of the bone surface and no extension into the surrounding soft tissues.

On computed tomography, the lesion is usually seen as an area of mild increased bone density, the slight sclerosis already described, again without any destruction of the bone or any soft-tissue mass. The pattern of dark-on-T1, bright-on-T2, non-enhancing, contained, sclerotic and without soft-tissue extension is the signature that allows a benign notochordal cell tumour to be recognised with confidence in the typical case.

The reason benign notochordal cell tumours attract attention out of all proportion to the trouble they cause is their relationship to chordoma. A chordoma is a rare, slow-growing but genuinely malignant bone tumour that also arises from notochordal cells and occurs in the very same locations, the sacrum, the clivus and the spine. Because the two share an origin and a habitat, telling them apart is the central task whenever a notochordal lesion is found.

Fortunately, in most cases the distinction can be made on imaging. A benign notochordal cell tumour stays within the bone, leaves the bone intact or slightly denser, has a tidy margin, does not enhance with contrast and forms no soft-tissue mass. A chordoma, by contrast, tends to destroy bone, enhances variably after contrast, and characteristically extends beyond the bone to form a soft-tissue mass that may press on adjacent structures. Both lesions share the same cellular marker, brachyury, which is one reason a small biopsy sample alone can sometimes be misleading.

One of the most actively discussed questions in this field is whether benign notochordal cell tumours are simply harmless leftovers, or whether some of them represent the soil from which a chordoma may, very occasionally, grow. Chordomas and benign notochordal cell tumours arise from the same cells, occur in the same places and share the same molecular markers. There are reported cases in which a chordoma was found arising alongside, or apparently within, a pre-existing benign notochordal cell tumour.

The current understanding is that some notochordal lesions appear to sit on a spectrum, ranging from entirely benign rests through benign notochordal cell tumours to overtly malignant chordoma, and that, under certain circumstances, a benign notochordal cell tumour might in rare instances be a precursor of chordoma. At the same time, the great majority of benign notochordal cell tumours never behave in this way and remain harmless throughout life.

With benign notochordal cell tumours the prevailing view in the literature is that when the imaging features are typical, biopsy is generally neither necessary nor advisable, and that careful imaging surveillance is the more appropriate first step. A biopsy of such a lesion can be actively misleading, because the benign notochordal cells share their cellular markers, including brachyury, with chordoma, so a small fragment can be misinterpreted. There are documented cases in which an unnecessary biopsy of a typical benign notochordal cell tumour led to a misdiagnosis of chordoma and, in turn, to unnecessary surgery.

Surveillance is the course described for the typical, benign-appearing lesion. A widely cited set of features used to support this approach includes the absence of any related neurological problem, well-corticated bony margins, a size below roughly thirty-five millimetres, no enhancement with contrast, no soft-tissue extension, no penetration of the lining of the spinal canal, and no progression on scans.

In published series of benign-appearing notochordal lesions followed over time, the lesions have generally remained stable. A retrospective series of incidental benign-appearing notochordal lesions of the clivus, for example, reported that all the lesions remained stable over a median follow-up of close to three years. Specialist and multidisciplinary input is a recurring theme, particularly for lesions in the clivus or sacrum, or for any lesion with atypical features. Intervention is not the path for the typical benign notochordal cell tumour; surgery and other active treatments belong to the management of chordoma.

The outlook with a benign notochordal cell tumour is, for the overwhelming majority of people, entirely reassuring. By its nature the lesion is benign, contained within the bone, non-destructive and usually silent, and the published follow-up series describe these lesions as remaining stable over years of observation. The element of caution that surrounds these lesions arises almost entirely from their kinship with chordoma, and is best understood not as alarm but as sensible vigilance.

This page is general medical education and is not a substitute for individual advice. Any new or worsening neurological symptoms require prompt medical assessment.

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This information is for general patient education and is not a substitute for an individual consultation. Always seek personalised advice from a qualified spinal specialist.