There are many fossae in the body, some of which include the digastric fossa (a depression on the inner surface of the mandible, giving attachment to the anterior belly of the digastric muscle), the hyaloid fossa (a depression in the front of the vitreous body, holding the lens of the eye) and the popliteal fossa ( the depression in the posterior region of the knee).
The word fossa comes from the Latin work for "ditch". The Fosse Way was a Roman road in England that linked Exeter in South West England to Lincoln in the East Midlands. It was probably called this from the ditch on either side of it. Many sections of the Fosse Way form parts of modern roads and lanes:
In some normal individuals, there is an additional fossa in the roof of the acetabulum, called the supraacetabular fossa. This fossa can be seen on high-resolution hip MRI scans. This area is present in a small percentage of normal, asymptomatic individuals, and should not be mistaken for an osteochondral lesion. Coronal intermediate and intermediate fatsat MRI images from a fifteen year-old female teenager, demonstrating the supraacetabular fossa:
The supraacetabular fossa is characteristically located at the 12:00 position of the acetabulum. The underlying bone marrow will be normal in signal. In some patients, it may be bilateral, although not always in a symmetric fashion.
Here is another example, from the right hip of a twenty-nine year old man:
The supraacetabular fossa is a pit in the vicinity of the stellate crease of the acetabulum but is separate from it (Richard Villar MD, personal communication). The stellate crease is a shallow puckering in the articular cartilage of the acetabulum:
© J Anat., 1997
In this arthroscopic image (Santori & Villar; J. Anat. 191:461-463, 1997) the acetabular fossa is at the bottom left and the margin of the acetabulum is at the top right. The stellate crease is outlined by the red arrows. The green arrow denotes a variably present groove ('iliopubic groove") that may be a result of incomplete fusion of the triradiate cartilage (Santori & Villar; J. Anat. 191:461-463, 1997).
The stellate crease is below the resolution of current clinical MRI scanners. The supraacetabular fossa is a separate, distinct entity, and can be detected using current MRI scanners. The supraacetabular fossa is a normal variant, and should not be mistaken for a pathologic condition.
Vic David MD