Benign notochordal cell tumor

Benign notochordal cell tumors are vertebral lesions that are usually asymptomatic and discovered incidentally on imaging of the head or spine. As this is a poorly-recognized entity, it can often be confused with aggressive vertebral lesions, such as a chordoma, when it is seen on imaging.

Terminology

Initially, the term vertebral intraosseous chordoma was used ⁷, although given that the relationship between these lesions and chordomas remains uncertain it is probably best to avoid this term. Other terms that have been used include giant (vertebral) notochordal rest and giant notochordal hamartoma (of intraosseous origin) ^3,9.

Diagnosis

There no defined diagnostic criteria for benign notochordal cell tumor although the following are generally accepted ⁹:

• no neurological symptoms

• well-corticated margins

• <35 mm in size

• no enhancement on imaging

• no soft tissue extension or dural penetration

• no progression on scans

• histologic absence of extracellular myxoid matrix and a low Ki67 index if biopsy performed

Epidemiology

Autopsy studies show benign notochordal cell tumors are extremely common with a reported incidence of up to 20% in cadaveric specimens ¹. While only the larger of these lesions can be seen on imaging it is felt they are under-reported ². 

Clinical presentation

The vast majority of lesions are asymptomatic but a small proportion of patients can present with chronic back pain and coccydynia ².

Pathology

Location

The distribution is similar to chordomas:

• clivus (50%)

• vertebrae

• sacrum/coccyx

Radiographic features

CT

• vertebral body sclerosis: can extend to the cortex or involve the entire vertebra

• preserved trabeculae

• no cortical destruction

MRI

• well-defined osseous lesions

  • T1: hypo- or isointense; may demonstrate hyperintense intra-lesional punctiform foci representing fat lobules due to entrapped bone marrow

  • T2: hyperintense

  • T1 C+ (Gd): usually no enhancement (enhancement is considered an atypical feature) ⁹

  • DWI/ADC: no restricted diffusion

• no soft tissue mass

Nuclear medicine

Often show no uptake on bone scintigraphy.

Treatment and prognosis

While there is a consensus that no specific treatment is required for asymptomatic lesions, the long-term malignant potential of benign notochordal cell tumors to transform into chordomas is not known and many advocate interval follow-ups ⁵.

Surgical resection or biopsy is generally reserved for lesions with atypical imaging features ⁹.

In most instances they are quiescent but reports of these tumors co-existing with chordomas or perhaps degenerating/transforming into chordomas exist ^8,9. 

Differential diagnosis

• chordoma ³

  • bony destruction on CT

  • soft tissue mass

  • enhance on MRI

• ecchordosis physaliphora

  • clivus

  • small and often pedunculated 

• notochordal vestiges of the intervertebral disc