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Breast Imaging |
1 From the Department of Radiology, University of São Paulo School of Medicine, São Paulo, Brazil. From the 2000 RSNA scientific assembly. Received April 19, 2000; revision requested May 26; revision received July 14; accepted August 2. Address correspondence to N.d.B., Rua Sampaio Vidal, 185, São Paulo-SP 01443-000, Brazil (e-mail: nestorbarros@uol.com.br).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMaterials and MethodsDiscussionREFERENCES |
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Index terms: Breast, abscess, 00.73 • Breast, calcification, 00.81 • Breast, diseases, 00.73 • Breast, US, 00.1298 • Skin, diseases, 06.73
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsDiscussionREFERENCES |
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Materials and Methods |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsDiscussionREFERENCES |
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Five women (age range, 42–83 years; mean age, 56.8 years) formed the study group. Three patients were from the countryside of Brazil, and two patients reported a recent trip to the countryside of Brazil. None of the patients reported a history of mosquito bites. All five patients presented clinically with palpable lumps associated with inflammatory signs 15–30 days prior to the imaging studies. One patient reported serous hemorrhagic drainage through the skin, and one described uncharacteristic pain.
The right breast was affected in three patients and the left breast in two patients. The location of the lump was retroareolar in three patients and deeper in the inferior and lateral portions of the breasts in the remaining two patients.
Mammography (Senographe 600 T, General Electric, Issy Les Moulineaux, France; or Mamo BC, Philips, Best, the Netherlands) showed an ill-defined mass 0.7–2.0 cm (mean, 1.3 cm) in diameter in all of the patients (Figs 1a, 2a). In three patients (Fig 1a), the masses were associated with two linear microcalcifications located in the periphery of the masses in a paired distribution. In one patient (Fig 1), the two radiolucent stripes were associated with the microcalcifications.
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Surgical excision was performed in three patients. The other two patients extracted the larva themselves. Radiography of one larva was performed after its surgical removal (Fig 1b).
In an attempt to study radiographic aspects of the larvae, we radiographed D hominis larvae from dogs. In these radiographs, we identified two parallel radiolucent stripes along the length of each larva, beginning at the two linear microcalcifications and ending at the most tapered portion of the larva (Fig 4a). This most tapered portion of the larva corresponds to the spiracles. A photograph (Fig 4b) of the two larvae shows larval stage L2, which typically has a tapered end, and larval stage L3, which typically has a cylindric shape. Both stages L2 and L3 have the typical dark concentric rows of bristles.
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Discussion |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsDiscussionREFERENCES |
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Myiasis caused by D hominis is absent in the Caribbean countries, with the exception of Trinidad (6). The furuncle-type myiasis caused by this insect has been described sporadically in developed countries, always in patients with a history of a recent trip to Mexico, Central America, or South America (2,4,6–17). In these regions, myiasis is caused by D hominis (botfly, macaw worm, or tropical botfly) larvae (4). It also has been described in patients who reported trips to tropical Africa or who live there, where the disease is referred to as "tumbu" and is caused by Cordylobia anthropophaga (3,18). The disease is rare in North America (19,20), where it may be caused by the Cuterebra genus of botfly. Myiasis is more likely to affect animals than humans (8). The endemic occurrence of furuncle-type myiasis has been associated with living close to forests or in the countryside.
In a mechanism known as phoresis, the botfly catches another kind of fly during flight and attaches her eggs to the other fly’s abdomen (4,5,8,17). These eggs also may be placed on other blood-sucking arthropods, such as ticks (3,8, 10,13,17,21). In these vectors, the first stage of larvae (L1) develop from these eggs (21). When the vectors contact a host, the cutaneous heat makes the botfly larvae emerge from the eggs and fall on exposed skin (4,8,9,16). There are only two reports (1,2) in the literature of the occurrence of this disease caused by D hominis in the breast, and this can be explained by the deposition of eggs in humid clothes or botfly larvae directly on exposed breasts. The former mechanism explains the third reported case (3), which was caused by C anthropophaga larva.
When over the host, the larva actively penetrates normal skin (8,13,16) or the orifice made by the intermediate fly (8). The larva remains in the subcutaneous tissue (13,17) below the skin orifice until it reaches maturity (17), without migrating to deeper structures (16). However, there have been two reports (8,9) of fatal cases of cerebral infestation caused by the migration of the larvae through the open fontanels in children.
After invading the skin, the larva creates a cavity similar to a long-neck bottle (9,16,17), with an opening to the skin that allows it to breathe (9,16) and eliminate larval excretions (13). The larva possesses two spiracles that give origin to two tracheas (12), and these are located in the posterior portion of the larva, close to the skin (17). The two radiolucent stripes noted on the mammogram in one patient likely correspond to this respiratory tract. These spiracles eventually can be seen as two black dots (4) protruding through the skin orifice (9).
The elongated larva (L1) becomes wider in its anterior and deeper portion (L2), assuming a flask shape (8). The posterior portion progressively enlarges until it reaches the fusiform or cylindric shape of the mature larva (L3). In this stage, the larva averages 1.5–3.0 cm in its largest diameter (8,9). Mature larvae reveal surface concentric rows of bristles in their full extension (9,12,17), as also seen in stage L2. The knowledge and identification of different larval stages may help in the appropriate treatment decision.
The mouth of a larva contains two small pharyngeal bones (16) also described as two sickle-shaped hooks (4,12). The paired linear microcalcifications observed on the mammograms in three of the patients in our study seem to correspond to these oropharyngeal structures. Symptoms of myiasis are usually observed during the 1st week of clinical evolution (8). The site of skin entrance usually appears as a pruriginous elevated lesion similar to a mosquito bite (5,8, 9,16), whether or not it is related to a mosquito bite (16).
After 2 or 3 weeks, a furuncle is formed (8,9). In this phase, the typical presentation is as a firm and red subcutaneous nodule (furuncle-like) (7,13,14), ranging in size from 1 to 3 cm (5,7,9). An intermittent serohemorrhagic or purulent drainage, representing larval excretions or secondary infection, occasionally emerges from the 4-mm-diameter skin orifice (4, 9,14) through which the larva breathes (9,13). Both the skin orifice and fluid drainage can be difficult to document (13), which is consistent with our findings. A magnifying lens can be helpful in detecting the cutaneous orifice (3) and identifying the moving spiracles (7,9).
Possibly due to larval movement, an intermittent pain that lasts for 1–2 minutes (5,8,9,13,15) and a sensation of movement under the skin are reported by some patients (4,5,9). Each nodular lesion contains one larva (13). Although multiple lesions may occur (10,16), there are rarely more than four or five lesions (15).
The diagnosis is mainly clinical when the presentation is typical (3,9,10,13). A diagnosis of myiasis should be considered in any patient who has a history of recent travel to an endemic area and develops a furunclelike lesion after a mosquito bite; such a diagnosis is especially likely if the lesion demonstrates characteristic drainage through the skin (8,9, 13,14). The diagnosis of myiasis is confirmed by removal of the larva or after histopathologic examination of surgically excised tissue (1,2,8,10,12–14,18).
In the English-language literature (4,8– 10,16,18,22), cutaneous myiasis has been misdiagnosed as regular mosquito bites, cellulitis, various infectious diseases (eg, furuncle, adenopathy, herpes zoster, and leishmaniosis), delusional parasitosis, and disease simulation. In many cases, the initial diagnosis was just a furuncle or cellulitis that was unresponsive to treatment with antibiotics (9). The cases of breast myiasis previously reported were initially diagnosed as periductal mastitis with skin fistulization (1), a benign-appearing mass with microcalcifications (2), and inflammatory carcinoma (3).
The mammographic features of the cases of breast myiasis in our study, namely ill-defined masses associated with microcalcifications, did not allow exclusion of malignancy, even in the presence of inflammatory signs. However, the first cases of breast myiasis made us aware of this condition so that myiasis was included in the differential diagnosis in subsequent cases. In contrast, US demonstrated the characteristic appearance of a hyperechoic mass representing the larva surrounded by a hypoechoic halo representing the cavity, as previously illustrated in the literature (11). The strong posterior acoustic shadowing identified in two cases may reflect the external coating of the larva. Definitive diagnosis of myiasis can be achieved if larval movement is detected at US, as was observed in one of the patients in our study.
The larval movement detected at US in one patient was initially attributed to thick fluid within the abscess, until the possibility of myiasis was considered. This emphasizes that clinical suspicion is the first step to correctly diagnosing myiasis (10,13). If the active movement of the larva is not detected at US, the differential diagnosis of myiasis, when affecting the breast, should include abscess, intraductal papilloma, cysts with thick hemorrhagic fluid, intracystic tumors, and complex cysts (23,24), as well as a dilated duct with thick fluid and a skin fistula. However, the acute onset of symptoms, the presence of inflammatory nodules, and the characteristic US features allow the differentiation of breast myiasis from many of these other diagnoses.
It has not been documented in the literature whether the type of microcalcifications observed in the patients in our study can be found with larvae other than D hominis larvae. It is possible that the masses visible at mammography and the hyperechoic larvae and hypoechoic cavities depicted at US may be seen with all types of larvae. The identification of active movement of the larva must be possible for all kinds of larvae, since they are alive.
The goal of treatment is to remove the larva and treat the eventual associated infection with antibiotics (4,7,9,13). The lesion heals rapidly after the larva is removed (4,9) or it spontaneously exits (4,8,9), which can occur in 46 days to 3 months (8,9). One method of removing larva is by obstructing the cutaneous orifice. This causes the larva to wiggle out of its tunnel as it attempts to breathe, which facilitates its removal (13). Various substances have been used for this purpose, including oil, petroleum jelly, butter, chewing gum, bacon, paraffin, and adhesive tape (4,5,7– 10,13,15,16), as well as toxic substances such as tobacco and ashes (4,8,9,16). The majority of recent reports (4,8–10) state that a subcutaneous injection of lidocaine may be used to numb the skin and the larva, which allows a small incision to facilitate extraction. In most reports, however, the larvae came out spontaneously or were extracted manually by the patients themselves.
In conclusion, knowledge of the clinical and imaging features of breast myiasis allows a correct diagnosis in patients with a breast lump and a history of recent travel to endemic areas. The detection of active movement of the larva at US examination is helpful and leads to the correct diagnosis and treatment while avoiding the more aggressive therapy associated with misdiagnosis of malignancy.
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FOOTNOTES |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMaterials and MethodsDiscussionREFERENCES |
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This article has been cited by other articles:
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  A. A. Shi, D. Georgian-Smith, L. D. Cornell, E. A. Rafferty, M. Staffa, K. Hughes, and D. B. Kopans Radiological Reasoning: Male Breast Mass with Calcifications Am. J. Roentgenol., December 1, 2005; 185(6_Supplement): S205 - S210. [Abstract] [Full Text] [PDF]
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