Tuesday, March 15, 2011

Supernovas and Hand Creases

NASA’s Chandra X-ray observatory has given us this image of an unusual hand-shaped nebula, a result of a star gone supernova. The pulsar remaining from this supernova spins at seven complete rotations a second, expelling particles and gas into space, creating the fingers of the hand.

Closer to earth, our hands are critical parts of being human, enabling us to caress, grasp tools, and change the world around us. As part of our body, the hand falls prey to many of the ills that affect all our tissues, including tumors. Some of these tumors must be excised by the hand surgeon, and when that is necessary, the creases of the hand can become important anatomic landmarks for the surgeon.

While radiologists are used to describing lesions in reference to easily observable deep structures such as bones and joints, it is often more useful to describe lesions with reference to surface landmarks. In the hand, one should remember that skin creases are not in the same position as the underlying joint. Hand skin creases are named as follows:

The surface anatomy of the hand was reviewed by Bugbee and Botte in 1993 (Clin Orth and Rel Res, 296: 122-126, 1993). In this diagram, the position of the skin creases is depicted by lines:

Bugbee and Botte point out the following:
---> DIP crease is consistently proximal to the DIP joint, with a mean distance of 7-7.8 mm proximal to the joint.

---> PIP crease is consistently proximal to the PIP joint, with a mean distance of 1.6-2.6 mm proximal to the joint.

---> palmar digital crease is consistently distal to the MCP joint, with a mean distance of 14.4-19.6 mm distal to the joint.

---> distal palmar crease averages 7.9 mm proximal to the little finger MCP joint, 10.3 mm proximal to the ring finger MCP joint, and 6.9 mm proximal to the long finger MCP joint.

---> proximal palmar crease averaged 9.1 mm proximal to the index MCP joint, 18 mm proximal to the long finger MCP joint, and 22.1 mm proximal to the ring MCP joint.

The MRI correlate is seen in this sagittal T2 fatsat image:

Green arrow = palmar digital crease; Red arrow = distal palmar crease; Blue arrow = proximal palmar crease.

The distal and proximal palmar creases can sometimes be identified on MRI by the presence of air between the skin folds.
Coronal T1 weighted images, posterior to anterior, depict air in the distal palmar crease (red arrow) and the proximal palmar crease (blue arrow):

This movie better depicts the various hand creases, in relation to the underlying joints:

Green arrow = palmar digital crease; Red arrow = distal palmar crease; Blue arrow = proximal palmar crease; Yellow arrow = thenar crease.

In this case, a 47 year- old male came to the hand surgeon complaining of focal pain along the palmar surface of hand. No mass was present on physical examination. The patient was referred for an MRI, to localize a suspected glomus tumor.

An axial gradient echo image reveals a 2 mm mass (red arrow) near the site of pain:

A coronal T1 weighted image also depicts the mass, which was not palpable:

The location of the lesion with respect to surface landmarks is best depicted on this sagittal T1 weighted image:

The lesion (red arrow) is located proximal to the palmar digital crease (green arrow), distal to the metacarpophalangeal joint (yellow arrow).

MRI precisely localized of the tumor in reference to the surface landmark, and enabled the surgeon to make the appropriate incision, and excise the tumor easily. Pathologic analysis confirmed the presence of a glomus tumor.

Vic David MD