AJR 2003; 180:665-668
© American Roentgen Ray Society
New Radiographic Classification of Bone Involvement in Pedal Mycetoma
Mohamed E. Abd El Bagi1,2
1 Mycetoma Research Centre, Soba Teaching Hospital, Faculty of Medicine,
Khartoum University, Khartoum, Sudan.
2 Present address: Internal Mail 920W, Military Hospital, P. O. Box 7897, Riyadh
11159, Kingdom of Saudi Arabia.
Received July 8, 2002;
accepted after revision August 22, 2002.
Address correspondence to M. E. Abd El Bagi.
Abstract
OBJECTIVE. The purpose of this study was to classify the pattern,
extent, and severity of bone involvement in mycetoma of the foot.
CONCLUSION. In this classification, stage 0 indicates the presence
of soft-tissue swelling without bone involvement. Stage I refers to the
extrinsic pressure effects on the intact bones in the vicinity of an expanding
granuloma. Stage II results from irritation of the bone surface without actual
intraosseous invasion. Cortical erosion and central cavitation occur in stage
III. If the disease spreads longitudinally along a single ray, stage IV is
established; horizontal spread along a single row represents stage V.
Multidirectional spread due to uncontrolled infection is classified as stage
VI.
Introduction
Mycetoma is a debilitating chronic granulomatous disease that is prevalent
in tropical and subtropical regions
[1,
2]. It is not unknown in Europe
and the United States [1]. The
disease may be caused by a fungus (eumycetoma) or by bacteria (actinomycetoma)
[1,
2,
3]. Mycetoma has been called a
sinister disease [4]. The
infection painlessly burrows deeply until it reaches the bone.
Clinical examination alone may not detect bone involvement. Modern
chemotherapeutic agents are efficient, particularly in early stages and in
combination with surgery [5].
However, amputation is necessary in 25-50% of patients, leading to disastrous
social and psychologic consequences
[2,
6]. Moreover, the rate of
postoperative recurrence varies from 20% to 90% and may lead to further
amputation [2]. Difficulty in
accurately identifying the limits and spread of the disease during surgery is
the chief reason for recurrence. The clinical features of mycetoma do not
always provide a reliable measure of the extent and spread of the disease
because some small lesions with few sinuses may have extensive spread in the
deep tissues and many connecting tracts. The objective of this article is to
classify bone changes in mycetoma of the foot.
Materials and Methods
The radiographic records of 516 patients who were seen at the referred
outpatient clinic of the Mycetoma Research Centre of the University of
Khartoum were reviewed. Three hundred ninety-nine (77%) of those patients were
males and 117 (23%) were females. Their ages ranged from 4 to 65 years; their
mean age was 27.4 years. All patients had been diagnosed as having mycetoma on
the basis of clinical or laboratory tests. The clinical diagnosis was based on
the characteristic triad of painless soft-tissue swelling, skin sinuses, and
discharge of colored grains (black, yellow, red, or white). The laboratory
test used in diagnosis was either aspiration cytology or the more successful
deep surgical biopsy.
Each patient's age and sex were noted as part of the study. Only
radiographs were included: no patient underwent linear tomography, CT, or MR
imaging; sonographic examinations, if performed, were not reviewed for this
study. The radiographic parameters recorded included the type of bone
involvement, the direction and pattern of the disease spread, and the location
of bone lesions in the foot. Radiographic classification was based on
radiographs obtained at the time of first presentation to the mycetoma
clinic.
Results
Table 1 summarizes the
patterns of spread and the different stages of bone involvement in mycetoma.
Infection usually follows a thorn prick in contaminated soil. A granulomatous
soft-tissue reaction surrounds the entry site, causing a localized increase in
the soft-tissue volume that may progress to a soft-tissue mass (stage 0)
(Fig. 1). These soft-tissue
swellings become nodular, hard, and expansive. Initially, the bone is
displaced, bowed, or compressed from one or both sides (stage I). No bone
invasion occurs at this stage (Fig.
2). The next stage occurs when the organism irritates the bone
surface before reaching the intraosseous compartment (stage II). This
irritation causes one of two osteoblastic responses: a periosteal reaction or
a diffuse reactive sclerosis (Fig.
3). Penetration of the periosteum and cortex leads to formation of
bone cavities. Cavitation can be limited to a solitary bone (stage III)
(Fig. 4). Peculiarly, the
infection may spread longitudinally along only one adjacent ray of metatarsal
bone and phalanx (stage IV) (Fig.
5). Horizontal spread will involve more than one ray but is
limited to one or two contiguous rows of small bones. This horizontal spread
represents stage V (Fig. 6). The infection may infiltrate the forefoot, midfoot, or hindfoot. When the
infection is neglected or uncontrolled, it spreads in more than one direction
and destroys most of the bones in the foot, leading to total disorganization
and mutilation of the foot structure (stage VI)
(Fig. 7).
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Fig. 1. —Preinvasive stage of pedal mycetoma. Frontal radiograph shows
right forefoot of 23-year-old man with soft-tissue swelling (arrow)
at medial aspect of dorsum of foot due to mycetoma. Note absence of bone
invasion (stage 0).
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Fig. 2. —Preinvasive stage of pedal mycetoma. Frontal radiograph shows
right forefoot of 27-year-old man who presented with large soft-tissue
swelling of foot due to mycetoma. Space between first and second metatarsal
bones is widened. Scalloping and external cortical compression of second and
fourth metatarsals may be seen. No frank intraosseous invasion has occurred
(stage I).
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Fig. 3. —Preinvasive stage of pedal mycetoma. Oblique radiograph shows
left forefoot of 25-year-old man who presented with soft-tissue swelling at
dorsum of foot with skin sinuses draining black granules (black Madura).
Extensive bone sclerosis is noted. No intraosseous cavities are shown (stage
II).
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Fig. 4. —Solitary bone involvement with mycetoma. Frontal radiograph
shows right big toe of 30-year-old man who presented with swelling and small
draining sinus at tip of toe due to mycetoma. Two intraosseous cavities are
surrounded by little reactive sclerosis. Note that erosions are limited to
single bone in terminal phalanx (stage III).
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Fig. 5. —Single-ray invasion in pedal mycetoma. Frontal radiograph
shows left forefoot of 29-year-old man known to have soft-tissue swelling and
bone lesions due to mycetoma. Infection has spread longitudinally along whole
of second metatarsal bone into proximal phalanx of left second toe. No
horizontal spread has occurred (stage IV).
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Fig. 6. —Horizontal spread of pedal mycetoma. Frontal radiograph shows
right forefoot of 39-year-old man known to have mycetoma of foot with poor
response to medical treatment. Note resorption of tarsal bones and adjacent
proximal ends of metatarsal bones. Distal ends of metatarsal bones and
phalanges are spared (stage V).
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Fig. 7. —Multidirectional spread of pedal mycetoma. Oblique radiograph
shows right forefoot of 19-year-old man with advanced mycetoma of foot.
Midtarsal bones have vanished. Moth-eaten appearance of metatarsals involving
third and fourth proximal phalanges is visible. Hind foot is also invaded as
result of multidirectional uncontrolled spread (stage VI).
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Discussion
The radiographic signs of bone involvement in mycetoma are well described
[7,
8,
9,
10,
11,
12]. However, these and other
reports in the radiography literature are descriptive; they are not
sufficiently specific to bring about standardization of management protocols.
The most comprehensive report was by Davies
[8] from Uganda. In addition to
its meticulous description of bone lesions, this report classifies the disease
into the early stage of soft-tissue invasion, the stage of external cortical
invasion, and the final stage of spread within the whole bone. Davies
considered widening of the intertarsal spaces to be a late sign, whereas we
consider it an early sign that usually precedes actual bone invasion
(Fig. 2). Lewall et al.
[7] summarized the radiographic
signs and their incidence in bone mycetoma, but they did not classify the
different stages or direction of disease spread.
Radiographs only were analyzed for all of the patients included in the
study. Some patients from this center underwent sonography
[11], but those images were
not included in the study. None of the patients underwent CT, linear
tomography, or MR imaging, which are known to be more sensitive
[9,
10]. Czechowski et al.
[10] found that radiography
had a sensitivity of only 50% in a series of 20 patients. Early or minimal
soft-tissue reaction and minute cortical erosion can be missed totally by
radiography because of their small size
[4].
Despite the limitations of radiography, scrutiny of the available resource
cannot be overemphasized. Advanced imaging techniques are not available in the
districts where the disease is prevalent. MR imaging was available at the
hospital in which this study was conducted, but it was considered too
expensive to use in this situation. However, early detection of this disease,
at stage 0 or I, is necessary if major surgery is to be avoided. The cost of
surgery at a later stage for lesions missed on radiography at an earlier stage
exceeds the cost of obtaining an MR image.
The presence of bone irritation (stage II)
(Fig. 3) is a warning sign
indicating that the organism is no longer encapsulated and is poised to invade
bone circumferentially. In stage III, bone invasion has occurred and may
remain restricted to a single bone (Fig.
4). The infection may spread along the bone axis and further
longitudinally along a single ray of metatarsal bone and phalanges (stage IV)
(Fig. 5). A more aggressive
spread assumes a horizontal path, which implies invasion of the soft tissues
surrounding the tarsal bones and within the intermetatarsal spaces, thereby
encroaching into the muscles, tendons, nerves, and blood vessels (stage V)
(Fig. 6).
Finally, stage VI represents foot mutilation beyond salvage, and limb
amputation is unavoidable (Fig.
7).
This study did not correlate radiographic classification with clinical
staging or operative findings. Further studies involving clinical correlation
and follow-up radiography are necessary to assess the impact of this
classification system on the choice of surgical or medical treatment. This
study found that simple contrast-enhanced sinography, which is cheap and
locally available, was—surprisingly—not used. Sinograms could
depict the extent and complexity of the interconnected deep sinus tracts and
their exact relation to the intraosseous lesions. However, sinography is an
invasive procedure and should not be offered as a screening test.
This classification system is the first to correlate the severity of
disease and the direction of disease spread. The study is not an exhaustive
list of all radiographic signs of bone mycetoma but a specification of
parameters and indexes for the assessment of disease progress and treatment
protocol planning.
In conclusion, infection of the foot by mycetoma agents follows a
predictable pattern in its different stages according to the organism's
invasiveness, the host reaction, and, most importantly, the duration of the
disease. This suggested method of classification capitalizes on previous
reports and remolds them with new observations for a systematic approach.
Worsening of the stage on follow-up radiography should indicate treatment
failure. This classification system is likely to assist in disease description
and treatment planning as well as in the monitoring of treatment response.
Acknowledgments
I am grateful to A. H. Fahal for allowing me unlimited access to the
Mycetoma Research Centre records and to O. Abdul Wahab, H. Al Sheikh, and the
Department of Radiology staff for maximal cooperation. I am also grateful to
M. K. Taifoor and F. Osman for their invaluable assistance.
References
- Welsh O. Mycetoma. Semin Dermatol
1993;12:290
-295[Medline]
- Fahal AH, Hassan MA. Mycetoma. Br J Surg
1992;79:1138
-1141[Medline]
- Reeder MM. Tropical diseases of the foot. Semin
Roentgenol 1970;5:378
-390
- Abd El Bagi ME, Sammak B, Al Shahed M, et al. Rare bone infections
"excluding the spine." Eur Radiol
1999;9:1078
-1087[Medline]
- Mahgoub ES. Medical management of mycetoma. WHO
Bulletin 1976;54:303
-329
- Lynch JB. Mycetoma in the Sudan. Ann R Coll Surg
Engl 1964;35:319
-340
- Lewall D, Ofole S, Bendl B. Mycetoma. Skeletal
Radiol 1985;14:257
-262[Medline]
- Davies AGM. The bone changes of Madura foot: observations in Uganda
Africans. Radiology
1958;70:841
-847
- Sharif HS, Clark DC, Al Thagafi MA, et al. Mycetoma: comparison of
MR imaging with CT. Radiology
1991;178:865
-870[Abstract/Free Full Text]
- Czechowski J, Nork M, Haas D, Lestringant G, Ekelund L. MR and
other imaging methods in the investigation of mycetoma. Acta
Radiol 2001;42:24
-26[Medline]
- Fahal AH, Sheikh HA, Homeida MA, Arabi YE, Mahgoub ES.
Ultrasonographic imaging of mycetoma. Br J Surg
1997;84:1120
-1122[Medline]
- Carroll DS. Mycetoma pedis. Radiology
1949;53:81
-84[Medline]
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Abstract
Introduction
