Focal nodular marrow hyperplasia

Last revised by Henry Knipe on 13 Jan 2024

Focal nodular marrow hyperplasia is a rare, benign condition where there is a localized conversion of red/hematopoietic from yellow/fatty bone marrow. Its main relevance is of having a pseudotumor appearance mimicking skeletal metastases on MRI 1.

Most commonly located in the spine (~60%) but can also commonly occur in the femora, sacrum and ilium 2.

Focal nodular marrow hyperplasia is occult 3.

Focal nodular marrow hyperplasia can have mild medullary sclerosis but can often appear normal 2,3.

Focal nodular marrow hyperplasia appears as an ill-defined, solitary or multifocal round-to-oval lesion without marrow edema. The average size is ~20 mm (range 8-55 mm) 1,2

  • T1: iso to mild high signal to skeletal muscle; low signal to marrow
  • T2: low signal compared to skeletal muscle and marrow
  • T2FS/STIR: variable including isointense to yellow marrow
  • T1C+: no enhancement 1-3

Signal intensity drop of >20% between in-phase and out-of-phase quantitative chemical shift imaging (e.g. Dixon method) is shown in most (~90%) cases 2.

Normal uptake is demonstrated 2

Focal nodular marrow hyperplasia demonstrates mild increased uptake 2

  • skeletal metastases: T2 signal tends to be higher, <20% signal drop on chemical shift imaging 2

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