Benign Notochordal Cell Tumour

What it is. The benign notochordal cell tumour (BNCT) is a benign intraosseous tumour of notochordal remnant origin, arising along the path of the embryonic notochord - the clivus, the vertebral bodies and the sacrum. It sits within the notochordal tumour spectrum alongside its malignant relative, chordoma, and the two share their brachyury (TBXT) marker.

How common. Notochordal rests are common autopsy findings - BNCTs have been reported in up to about 20% of spines at autopsy (a widely repeated figure for which no primary autopsy series was retrieved here - treat it as an order of magnitude, not a measured prevalence). The vast majority remain stable, asymptomatic and undetected; only a tiny fraction come to clinical attention, usually as an incidental finding on axial imaging.

Who presents, and how. Reported biopsy-proven series are small: the largest (Iorgulescu 2013) describes 16 lesions in 8 adults identified on imaging performed for back pain - so "incidental" describes the lesion's relationship to the symptom, not a screening discovery. There is no established sex or age predilection from cohort data; reported cases are adults.

Why it matters. The entity exists as a clinical problem almost entirely because of its resemblance to - and possible precursor relationship with - chordoma. Recognising it avoids the morbidity of unnecessary oncological resection; missing a chordoma mislabelled as BNCT allows a malignant tumour to progress.

• The notochord and its remnants. The notochord is the embryonic axial midline structure; it normally regresses, its only adult remnant being the nucleus pulposus of the intervertebral disc. Notochordal cell rests persist in the clivus, vertebral bodies and sacrococcygeal region, and BNCT (also called a "giant notochordal rest/hamartoma") arises from these intraosseous rests.
• The extraosseous relative. Ecchordosis physaliphora is a related benign notochordal remnant that is extraosseous/intradural - classically on the dorsal clivus/prepontine region - the intracranial counterpart of the intraosseous BNCT.
• How common. Notochordal rests are common - BNCTs are found incidentally in up to about 20% of spines at autopsy - and most remain stable; only a small proportion behave as precursors, with some chordomas arising adjacent to a BNCT.
• The gene behind brachyury. Brachyury is the T-box transcription factor T (gene TBXT), the master regulator of notochord development, expressed in all notochordal cells (BNCT, chordoma and nucleus pulposus). Germline TBXT duplication and a common TBXT variant are chordoma susceptibility factors - the molecular basis of the shared marker and the precursor link.

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Treating destruction and soft-tissue extension as an absolute switch between observation and en-bloc surgery is clean but incomplete. A recognised intermediate group exists, and knowing it is what separates a safe answer from a confident one.

The typical story is no story at all - BNCT is characteristically asymptomatic and incidental, found on CT or MRI performed for unrelated reasons. When patients do present, the reported context is non-specific back or axial pain that prompts imaging (all 8 patients in the Iorgulescu series presented this way); the lesion is then an incidental finding rather than the proven pain generator.

Red flags that point away from BNCT and toward chordoma: progressive or night pain, neurological symptoms (radiculopathy, sacral plexus symptoms, bladder/bowel disturbance), a palpable presacral mass on rectal examination, and any imaging evidence of cortical destruction or a soft-tissue component. The Terzi cases all presented with subacute mild pain - including the one that harboured incipient chordoma - so symptoms alone do not separate the two; the imaging aggressiveness assessment does.

Examination is usually normal in BNCT. Any neurological finding or palpable mass should be treated as a chordoma until proved otherwise and referred to a specialist spine/tumour centre.

The lesion itself. In the available follow-up, biopsy-proven BNCTs do not progress: 0 of 16 lesions grew or became symptomatic at a median 21.6 months (Iorgulescu 2013), and the atypical-category cases were similarly indolent (one grew 3.7 mm over ten years; Carter 2017). The prognosis of a genuine BNCT is therefore excellent.

The complication that matters is transformation - or coexistence - with chordoma. BNCT is hypothesised to be a chordoma precursor (shared notochordal origin, shared brachyury), and the Terzi case proves an atypical notochordal lesion can harbour incipient chordoma. What no series provides is a rate: the cohorts are too small and too short to quantify transformation risk, which is precisely why surveillance has no validated stopping point.

The iatrogenic complications are the other half of the story. En-bloc sacral or spinal resection carries significant morbidity (as the Terzi resected case illustrates) - sacral nerve sacrifice, bladder/bowel and sexual dysfunction, wound and reconstruction problems. Over-calling a BNCT as chordoma inflicts that morbidity for a lesion that would never have harmed the patient. Both error directions are complications of the diagnosis, and both are minimised by specialist-centre review.

Surveillance as treatment. Interval imaging is the management and the safety net: it confirms stability, and it catches the rare lesion that declares itself aggressive early enough for curative resection. The schedule is set with the treating centre - no published protocol exists.