Characteristic radiographic findings are produced, including increased soft tissue thickness and bone overgrowth. Joint abnormalities result from proliferation of chondrocytes in articular cartilage. The radiographic features of joint involvement are joint space narrowing, bone sclerosis, cyst formation and osteophytosis, which resemble the changes of primary degenerative joint disease. Continued hypersecretion of growth hormone (somatotropin) affects both the mature and immature skeleton. In the immature skeleton, in which the growth plates are still open, the result is excessive growth of bone in both length and width, a condition known as hyperpituitary gigantism. This disorder is characterized by extreme height. In the mature skeleton, in which the growth plates have closed, growth hormone hypersecretion may reactivate endochondral bone formation at various existing cartilage  bone junctions, such as the costochondral junctions. Acromegaly can result in periosteal bone formation, leading to widening of osseous structures and enlargement of soft tissue. Such excessive growth is prominent particularly in the hands, feet and lower jaw and is termed acromegaly. Articular cartilage may be affected by a continuous cycle of fragmentation, disordered joint mechanics and attempted regenerative tissue repair with remodelling.

Radiographic features of skeletal involvement include changes in skin thickness and abnormalities of the skull, hand, foot, vertebral column, thoracic cage, pelvis and other sites. Hypertrophy of cartilage and degeneration of both cartilage and bone also are seen (Table 1) (Fig.1).

Certain bone and soft tissue measurements are of value in the diagnosis of acromegaly. Collagen tissue demonstrates a marked response to excessive amounts of growth hormone, manifested as thickening of the skin. Measurement of heel pad thickness (greater than 21.5 mm in women or 23 mm in men) can be suggestive or diagnostic of acromegaly. The sesamoid index (obtained by measuring the medial sesamoid at the first metacarpophalangeal joint and then multiplying this value by the greatest diameter of the same sesamoid image that is perpendicular to the first measurement), is another helpful measurement. A sesamoid index of greater than 40 in men and greater than 32 in women is suggestive of acromegaly. Other measurements that may indicate presence of the disease are a tuftal width of the third finger greater than 10 mm in women or 12 mm in men; joint space thickness of the second metacarpophalangeal joint of 2.5 mm in either men or women; and thickness of the phalangeal soft tissues of greater than 26 mm in women or 27 mm in men.

Although accurate diagnosis of acromegaly is not difficult, particularly in advanced cases, some of the individual radiographic signs may be noted in other disorders. An acromegaly-like syndrome has been associated with pachydermoperiostosis. Radiographic findings are similar to those of acromegaly, with enlarged sinuses, prominent supraorbital ridges, and thickening of the phalanges. However, the sella turcica is not enlarged, and severe prominence of the phalangeal tufts and enlargement of articular space are not observed.

Acromegaly, Table 1. Radiographic features in acromegaly.

Enlargement of costochondral junctions
Thickening of intervertebral discs
Mandibular enlargement
Thickening of the cranial vault
Prominence of the supraorbital ridges and facial structures
Cortical thickening of tubular bones
Enlargement of phala DR/RB DR/RB The Encyclopaedia of Medical Imaging Volume III 1		Acromegaly, Fig. 1 Typical radiographic features. a. Lateral radiograph of the skull demonstrates an enlarged sella turcica, increased thickness of the cranial vault, and prominent sinuses and supraorbital ridges. b. Lateral radiograph of the hindfoot demonstrates thickening of the soft tissues adjacent to the calcaneus. Note prominent calcaneal enthesophytes. c. PA radiograph of the hand demonstrates enlargement of the base of the terminal phalanges and pseudoforamina of the distal phalanges (arrow). Note the beak-like osteophytes on the medial aspects of the metacarpal heads (arrow), as well as at the distal radius and ulna (larger arrows). d. AP radiograph of the knee demonstrates widening of the knee joint space. e. AP radiograph of the pelvis demonstrates joint space narrowing in the hips and bony proliferation at ligament attachment sites.