Nodular lesion at the flexor tendon of the finger

A 58-year-old male presents with a slowly progressive nodule for 6 months on the volar side of the proximal phalanx of the left fifth digit.

A nodule is located on the volar side of the proximal interphalangeal joint of the left digit, contacting the superficial side of the flexor tendon. On a lateral radiograph (Fig. 1), a nonspecific soft tissue swelling is seen, with absent calcifications. A longitudinal sonographic view (Fig. 2) demonstrates a hypoechoic lesion with Doppler signal at the periphery. On T1-weighted images (T1-WI), the lesion is isointense to muscle tissue (Fig. 3). On fat-suppressed T1-WI, the nodule is of heterogeneous signal (Fig. 4). On T2-WI, the lesion is heterogeneous with intralesional areas of intermediate and high signal intensity (Fig. 5). On fat-suppressed T2-WI, a predominant hyperintense signal is seen (Fig. 6). On T2* sequences, there is no significant blooming artefact (Fig. 7).  After IV administration of gadolinium contrast, there is vivid, predominantly peripheral contrast enhancement (Fig. 8).

The resection specimen shows a whitish nodule, compatible with a gouty tophus (Fig. 9). Past history included acute gout in both first metatarsophalangeal joints, 8 years previously, for which he was treated by colchicine. His uric acid level was slightly elevated.

A gouty tophus typically represents a chronic granulomatous inflammatory response to a central core of monosodium urate crystals surrounded by a cellular and fibrovascular zone. Typically, they manifest years after an initial, acute gout arthritis, in the context of long-standing hyperuricemia [1]. De novo presentation has been described as well [1].

Macroscopically, soft tissue tophi appear as white nodules. Typical locations are the first metatarsophalangeal joint, olecranon, patella, Achilles tendon, ear and the volar side of the distal phalanges of the fingers [1,2]. Hands and wrist are often affected in advanced cases, most commonly the interphalangeal joints [2].

On conventional radiographs, gouty tophi typically have an intermediate to high density. In patients without renal insufficiency, they may calcify. When present, erosions in the adjacent bone are typically peri-articularly located, well-circumscribed with overhanging edges and parallel to the long axis of the bone. Involvement of the articular surface is a late manifestation [3]. On ultrasound, tophi have a heterogeneously hypoechogenic appearance, with peripheral increased Doppler signal [2]. Ultrasound may also depict the relationship with the adjacent tendon and osseous pressure erosions [2,4]. Gouty tophi have rather nonspecific MRI findings. They are of low to intermediate signal intensity on T1-WI and of variable signal on T2-WI, usually heterogeneously low to intermediate. They demonstrate marked enhancement [5]. Dual-energy CT can be used to detect urate crystals. This technique has a high sensitivity, but recent studies show that it has a false-positive rate of 30% in wrist arthropathies with a limited value in acute gout [6,7]. The differential diagnosis of tophaceous gout at the flexor tendons of the finger includes a giant cell tumour of the tendon, characterized by a blooming artefact on T2* sequences due to intralesional hemosiderin deposition [8]. Synovial cell sarcomas are primarily para-articularly located and contain haemorrhagic foci, being of high signal on T1-WI [9]. Melanoma should also be included in the differential diagnosis. Tendon fibroma has also a predilection for hands and feet (10).

Tophaceous gout should be included in the differential diagnosis of nodular lesions of the flexor tendon. Correlation of imaging and clinical history is the clue to the diagnosis.