Metatarsalgias: differential diagnosis with magnetic resonance imaging

Abstracts

Várias lesões podem causar metatarsalgia, cujas manifestações clínicas podem ser inespecíficas. As imagens de ressonância magnética, associadas a outros métodos de imagem e dados clínicos, freqüentemente podem contribuir na detecção dessas lesões e possibilitar que um diagnóstico relativamente preciso seja considerado. Nosso objetivo é descrever e ilustrar, por meio de imagens de ressonância magnética, as principais doenças que causam metatarsalgia.

Metatarsalgia; Doenças do pé; Artropatias; Imagem por ressonância magnética

ICONOGRAPHIC ESSAY

Metatarsalgias: differential diagnosis with magnetic resonance imaging^*

Maria Carolina Guimarães^I; Claudia Kazue Yamaguchi^II; André Yui Aihara^III; Luiz Guilherme Hartmann^III; Jorge Pröglhöf^I; Artur da Rocha Corrêa Fernandes^IV

^IMD Radiologists at Diagnósticos da América

^IIHead of the Musculoskeletal Sector at Service of Diagnostic Imaging, Hospital Santa Casa de Misericórdia de São Paulo, MD Radiologist at Diagnósticos da América

^IIIMD, Collaborators at Department of Diagnostic Imaging, Universidade Federal de São Paulo-Escola Paulista de Medicina, Radiologists at Diagnósticos da América

^IVAdjunct Doctor Professor at Department of Diagnostic Imaging, Universidade Federal de São Paulo-Escola Paulista de Medicina, Radiologist at Diagnósticos da América

^{Mailing address}

ABSTRACT

Several lesions may cause metatarsalgia whose clinical manifestations may be non-specific. Magnetic resonance imaging associated with other imaging methods and clinical data frequently can contribute to detection of these lesions, allowing a reasonably precise diagnosis to be considered. Our purpose is to describe and illustrate, by means of magnetic resonance imaging, main diseases causing metatarsalgia.

Keywords: Metatarsalgia; Foot diseases; Arthropathy; Magnetic resonance imaging.

INTRODUCTION

Metatarsalgia is a painful condition affecting the metatarsal – an area in the forefoot containing five bones — and may be related to soft, bone, articular and periarticular tissues^(1,2). Clinical manifestations in patients presenting metatarsalgia may be non-specific or atypical, with limited evaluation by means of conventional radiology, so further investigation utilizing magnetic resonance imaging (MRI) is indicated⁽³⁾. In the majority of cases, with MRI it is possible to define anatomical localization, lesion extent and involvement of adjacent structures, resulting in a more accurate diagnosis, besides allowing detection of associated occult lesions that may change the condition prognosis.

Our objective is to describe and illustrate main diseases causing metatarsalgia in an iconographic essay with MRI. With the aim of developing this essay, we have opted to divide metatarsalgia causes into: soft tissues tumorations, traumatic lesions, Freiberg infraction, sesamoid disorders, articular diseases and diabetic foot, in order to facilitate the differential diagnosis of the lesions.

NON-NEOPLASTIC SOFT TISSUES TUMORATION

A wide range of tumorations, the majority of them benign, affect feet and ankle, and the non-neoplastic ones, like Morton's neuroma, ganglia and plantar fibromatosis, are much more frequent than the true neoplasias⁽⁴⁾.

Morton's neuroma x bursitis

There are few conditions affecting the space between metatarsal heads and basically they are represented by Morton's neuroma and bursitis.

The interdigital neuroma, or Mortons's neuroma, is a common cause of metatarsalgia. It is a non-neoplastic lesion consisting of perineural fibrosis and nervous degeneration⁽³⁾. By definition, it is centered in the region of neurovascular band, between metatarsal heads (usually between the third and fourth rays) and under the deep transverse metatarsal ligament⁽⁵⁾. Morton's neuroma may be present in asymptomatic individuals⁽⁶⁾ and some studies propose a 5 mm minimum transverse diameter, besides association with compatible clinical findings, for a neuroma being considered as relevant at MRI^(5,7). The typical finding is a lesion with low or intermediate signal on T1 and low signal on T2-weighted images (representing the fibrous component of the lesion) and, usually, with moderate and homogeneous enhancement, more clearly identified on T2-weighted fat-suppressed sequences (Figure 1)⁽⁸⁾. The use of gadolinium is controversial^(9,10), but it is of help in differentiating between solid and cystic tumors like bursitis that frequently comes along with these intermetatarsal lesions⁽⁸⁾.

Figure 1 - click here to enlarge

Bursitis also may be present in cases of trauma, infection, rheumatoid arthritis, gout. Besides affecting intermetatarsal bursae (Figure 2), bursitis may occur in adventitious bursae (localized under the metatarsal heads) (Figure 3). They are characterized at MRI as well-defined liquid collections, presenting hyposignal on T1 and hypersignal on T2/STIR and peripheral enhancement after contrast agent injection⁽³⁾. Small collections with 3 mm or less in transverse diameter in the three first intermetatarsal bursae may be physiological⁽⁷⁾.

Figure 2 - click here to enlarge

Ganglia

Ganglia are cystic lesions with mucinous content and fibrous capsule. In the foot, ganglia usually occur on the dorsal region, adjacent to the articular capsule, tendinous sheath, tendon or ligament and, usually, there is no apparent connection with the articular space. Lesions present well delimited, usually with a lobulated aspect, with septations, hypointense or intermediate signal intensity on T1, hyperintense on T2-weighted images and fine peripheral contrast enhancement (Figure 4)^(4,6).

Figure 4 - click here to enlarge

Plantar fibromatosis

Plantar fibromatosis is characterized by a fibrous proliferation usually occurring on the medial and superficial aspect of the plantar fascia⁽³⁾. One or more nodules may be present, characterized by hyposignal or intermediate signal intensity on T1 and, in the majority of cases, hyposignal on T2-weighted images (Figure 5). Generally, there is no adjacent inflammatory edema. Contrast enhancement is variable^(3,11).

Figure 5 - click here to enlarge

TRAUMATIC LESIONS

Plantar plate disruption

The plantar plate is a fibrocartilaginous structure that reinforces the articular capsule of metatarsophalangeal joints. On T1 and T2-weighted MRI images, it is identified as a low signal intensity band, attached to the plantar aspect of the metatarsal head and that is inserted into the proximal phalanx basis, adjacent to the articular surface, deeply to the flexor tendons. Plantar plate ruptures may be related to acute traumatic events or sub-acute repetitive traumas (degenerative lesions)⁽⁵⁾.

Generally, acute traumatic lesions occur because of hyperextension forces placed on joints, the first metatarsophalangeal joint being the most commonly affected, resulting in complete or partial rupture of the plantar plate, characterized at MRI by increased signal and discontinuity of the plate and hypersignal of this structure, frequently associated with soft tissues edema, chondral and subchondral lesions (Figure 6)⁽³⁾. Degenerative lesions tend to occur from the second to the fifth metatarsophalangeal joints and most commonly in women who use high-heeled, pointed shoes. MRI findings include increased signal and discontinuity of the plantar plate on T2/STIR images, possibly associated with flexor tenosynovitis, metatarsophalangeal articulation synovitis and hyperextension of the proximal phalanx⁽¹²⁾.

Figure 6 - click here to enlarge

Ligaments lesions

MRI findings of collateral ligament acute lesions (Figure 7) include ligament discontinuity, disinsertion and thickening, associated with increased intraligament signal (edema/hemorrhage). Obliteration of adjacent fat planes and fluid accumulation in soft tissues also may be observed⁽¹³⁾.

Figure 7 - click here to enlarge

Stress fractures

Metatarsal stress fractures are frequent in runners, ballet dancers, military recruits and sports practitioners. Conditions resulting from biomechanical changes, including low longitudinal arc of the foot, hallux valgus, and recent surgery of the hallux, may increase the risk of developing a stress fracture⁽³⁾. The middle and distal portions of the second, third or fourth metatarsal shafts are most frequently involved. The fracture is characterized by a band of low signal intensity contiguous with the cortex, better identified on T2/STIR images, associated with marrow edema. Frequently, there is associated cortical thickening and adjacent soft tissues edema (Figure 8)⁽⁵⁾.

Figure 8 - click here to enlarge

FREIBERG INFRACTION

Freiberg infraction is a disorder affecting the metatarsal head (usually the second or third metatarsal head) and is characterized by collapse of the subchondral bone, osteonecrosis and chondral fissures. At MRI, Freiberg infraction is characterized as a well delimited area of hyposignal in the metatarsal head, with increased signal on T2/STIR images in acute phases, progressing to subchondral bone collapse, with flattening of the articular surface, epiphysis irregularity and bone marrow low signal on T2-weighted sequences (bone sclerosis) (Figure 9). In a later stage, reduction of the articular space and marginal osteophytosis occur⁽³⁾.

Figure 9 - click here to enlarge

SESAMOID DISORDERS

Main conditions affecting sesamoids are osteoarthrosis, sesamoiditis, stress lesions and osteonecrosis. The differential diagnosis may be difficult to establish in the early phase of the three latest conditions.

Sesamoiditis is an inflammatory condition produced by repetitive injury to the plantar aspect of the forefoot. MRI findings in the marrow of sesamoid bones include increased signal intensity on T2/STIR images, with decreased or normal signal intensity on T1-weighted images (Figure 10). The bone marrow signal intensity changes are similar to those caused by stress response and there may be some overlap between these conditions⁽¹⁴⁾.

Figure 10 - click here to enlarge

Stress lesions affect especially medial sesamoid that is larger and higher load bearing, and also may affect the synchondrosis between the portions of a bipartite sesamoid⁽¹⁴⁾. Sesamoid fractures usually are transverse and irregularly marginated, and present as a linear hyposignal image associated with marrow edema (Figure 11); adjacent soft tissue edema may be found⁽¹¹⁾.

Figure 11 - click here to enlarge

Osteonecrosis more frequently occurs in the lateral sesamoid. The initial MRI finding may be marrow edema similar to that found in sesamoiditis and stress lesions. Contrast enhancement may be quite variable. The diagnosis is easy in a later stage of osteonecrosis, characterized by cortical irregularity, bone collapse and cysts formation (Figure 12). Differentiation from osteoarthrosis is made by the presence of "kiss lesions" between metatarsal head and sesamoid and by adjacent articular changes (Figure 8)⁽¹⁴⁾.

Figure 12 - click here to enlarge

ARTICULAR DISEASES

Osteoarthrosis

Osteoarthrosis is a common finding in the first metatarsophalangeal joint and may involve sesamoids (Figure 8). A hallux valgus deformity may precipitate the degenerative process. MRI findings in osteoarthrosis include reduction of the articular space, marginal osteophytes, subchondral cysts (with "kiss" aspect on adjacent bone surfaces), subchondral, marrow edema and subchondral sclerosis⁽³⁾.

Rheumatoid arthritis

Rheumatoid arthritis commonly affects the feet. The earliest changes occur in the metatarsophalangeal joints⁽³⁾. If rheumatoid arthrosis is suspected, MRI should be the imaging method of choice, for allowing the early diagnosis by detection of synovitis and marrow edema^(15,16). Additional findings include marginal erosions, pannus (Figure 13), articular effusion, cartilage thinning, subchondral cysts, besides bursitis and tenosynovitis. The pannus presents hyposignal or intermediate signal intensity on T1 and hypersignal on T2-weighted images with homogeneous contrast enhancement (hypervascular) and, with the disease chronicity, fibrous pannus develops and hemosiderin deposition may occur, demonstrating low signal intensity on T2-weighted images⁽³⁾.

Figure 13 - click here to enlarge

Gout

Most commonly, gout affects the first metatarsophalangeal joint. Findings in the acute phase are non-specific and include joint effusion and synovial thickening. Tophaceous gout (Figure 14) represents the chronic form of the disease. Tophi may produce bone erosions and occur at intraarticular or periarticular locations or at a distance, manifesting as a soft-tissue mass. Tophi have intermediate to low-signal intensity on T1-weighted images and variable signal intensity on T2-weighted images, however, generally with heterogeneous low signal intensity suggesting the diagnosis. Marrow edema may occur adjacent to intraosseous tophus^(3,5).

Figure 14 - click here to enlarge

DIABETIC FOOT: OSTEOMYELITIS x NEUROARTHROPATY

Osteomyelitis is a common complication in diabetic patients and, generally, is resulting from spread of infection from an adjacent soft-tissue lesion. Most common locations of soft-tissue infections and osteomyelitis are the points suffering higher pressure like those under metatarsal heads and calcaneus where there may be skin ulcers. MRI findings include bone marrow hyposignal on T1-weighted and hypersignal on T2/STIR contrast-enhanced images. The presence of skin ulcers, cellulitis, abscess formation, fistulous tract, cortical discontinuity and gas formation evidence favor the likelihood of osteomyelitis (Figure 15). MRI findings in acute neuroarthropathy are similar to those of osteomyelitis, with the bone marrow presenting signs of edema (Figure 16). But, the location of the lesion on the middle foot at some distance from soft tissues, the polyarticular involvement and the absence of localized cortical lesions favor the diagnosis of neuroarthropathy. Findings in chronic neuroarthropathy include bone sclerosis (subchondral hyposignal on T1 and T2-weighted images), periarticular cysts formation, bone fragmentation, luxation, subluxation, joint effusion and soft-tissue edema^(17,18).

Figure 15 - click here to enlarge

CONCLUSION

In the evaluation of metatarsalgias, MRI findings associated with clinical history and physical examination data may be decisive for the diagnosis and/or staging of the lesion. The use of MRI combined with other imaging methods like plain X-ray, computed tomography and ultrasound frequently may bring relevant information for establishment of diagnosis and treatment conduct

REFERENCES

Received October 28, 2004.

Accepted after revision August 29, 2005.

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*

Study developed at Diagnósticos da América (Delboni/Lavoisier), São Paulo, SP, Brazil.

Publication Dates

• Publication in this collection
  26 Sept 2006
• Date of issue
  Aug 2006

History

• Accepted
  29 Aug 2005
• Received
  28 Oct 2004