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Oval fossa of right atrium

The oval fossa, also known as the fossa ovalis, is a depression in the interatrial septum of the right atrium. It represents the remnant of the foramen ovale, an essential fetal communication between the right and left atria that allows blood to bypass the pulmonary circulation before birth.

The fossa is typically located inferior to the limbus of the fossa ovalis, a raised muscular rim that represents the septum secundum. After birth, the foramen ovale normally closes when left atrial pressure exceeds right atrial pressure, leaving the oval fossa as a thin, fibrous depression. In some individuals, incomplete fusion results in a patent foramen ovale (PFO), which can serve as a potential pathway for paradoxical embolism and cryptogenic stroke.

Synonyms

  • Fossa ovalis

  • Oval fossa of interatrial septum

  • Depression of septum primum

Function

  • Fetal circulation: Allowed right-to-left shunting of oxygenated blood from placenta via foramen ovale

  • Postnatal role: Serves as a fibrous remnant marking site of closure

  • Clinical importance: Site of PFO, atrial septal defect (ASD), and interventional procedures (e.g., transseptal puncture)

MRI Appearance

T1-weighted images:

  • Appears as a thin, hypointense depression in the interatrial septum

  • Better appreciated with contrast sequences

T2 Cine (Cardiac-gated):

  • Cine imaging shows the oval fossa as a thin, mobile interatrial septal depression

  • In case of PFO/ASD, abnormal flow jets may be visible across the septum

  • Functional evaluation of interatrial shunting

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Septal tissue enhances uniformly

  • PFO or ASD may be seen as a contrast jet across the septum, with left-to-right or right-to-left shunting

  • Late gadolinium enhancement can show fibrosis around the fossa

MRI Non-Contrast Cardiac-Gated 3D Imaging:

  • Demonstrates the morphology of the fossa ovalis and adjacent interatrial septum

  • Useful in planning closure procedures and transseptal puncture in patients contraindicated for contrast

CT Appearance

Contrast-Enhanced CT (Cardiac CTA):

  • Demonstrates the oval fossa as a thin depression in the interatrial septum

  • PFO or ASD may be seen as a contrast jet or gap across the septum

  • 3D reconstructions allow detailed visualization of the septal anatomy for interventional planning

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Oval fossa of right atrium CT axial image -img-00000-00000

MRI image

Oval fossa of right atrium mri image