Diagnostic imaging of injuries caused by venomous and traumatogenic catfi sh

Injuries caused by fi sh are common in marine and freshwater environments. Catfi sh of the Ariidae and Pimelodidae families cause about 80% of those injuries. One of the complications of injuries caused by fi sh is the retention of fragments of the stinger in the wounds. Here we report fi ve cases (of a total of 127 injuries caused by catfi sh in the Brazilian coast) in which the retained fragments were detected by radiological examination. Retained fragments should be considered in patients stung by catfi sh. A simple X-ray is suffi cient to detect fragments of stingers in the wounds.


INTRODUCTION
The incidence of injuries caused by marine animals in Brazil is 0.1% (1 in 1,000 emergency cases) (1) .Marine catfi sh alone are responsible for about 80% of those injuries (1) (2) (3) (4) .The Ariidae (distributed worldwide) and Plotosidae (found in the Indo-Pacifi c region) are the most important families of catfi sh.Many marine catfi sh have three serrated stingers at the dorsal and pectoral fi ns that are used as a defense against predators (Figure 1).The stings of some species have venomous glands that can cause serious injuries with lacerations and envenomation in humans, often occurring in the hands and feet of fi shermen or beachgoers (2) .
Here, we review the cases of fi ve patients who were stung by catfi sh.This paper establishes a relationship between their clinical outcomes and the radiological fi ndings of retained fragments of the stinger, and discusses the importance of diagnostic imaging tools in injuries caused by venomous and traumatogenic catfi sh.

CASE REPORT
A series of 127 cases of injuries caused by catfi sh were registered in a ten-year period in the Brazilian coast: they occurred in Ubatuba town (Southeastern Brazil), Aracaju and Salvador Cities (Northeast region), and Salinópolis town (North region) (2) .Of the 127 cases, fi ve (3.9%) had retention of fragments of the stinger in the wounds.All 127 cases presented envenomation, manifested by intense local pain and infl ammation; they were treated with immersion of the affected member in hot water, with improvement of symptoms (1) (2) (3) .However, in the fi ve cases with retained fragments of the stinger, local infl ammation and pain persisted for more than 24 hoursthe time when the venom of catfi sh typically ceases its action.The patients returned to the hospital 1-5 days after the initial envenomation.Three patients had been stung in the feet, and two had been stung in the hands.
Due the late-stage edema, erythema and pain, the patients were submitted to conventional X-ray examination.The X-rays revealed fragments of the stinger and areas of infl ammation (Figure 1 and Figure 2).All fi ve patients underwent surgery for extracting the stingers, with complete resolution of late infl ammation (Figure 3).

Ethical considerations
The cases presented in this report are a part of previous studies that have been approved by the Ethics Committee of the Botucatu School of Medicine (São Paulo State University, São Paulo, Brazil).

DISCUSSION
Conventional radiography is often the first test to be performed in the investigation of foreign bodies.In appropriate circumstances, this exam allows us to assess the location, size, and number of foreign bodies (5) (6) (7) .A simple X-ray examination shows 98% sensitivity in detecting metal fragments and other radiopaque substances such as the stinger of catfi sh (7) (10) (11) .The anteroposterior, profi le and oblique incidences allow not only to rule out the presence of fragments of stinger, but also gas in the soft tissues or a secondary bacterial infection, and to evaluate the depth of the sting, choice of surgical approach, and possible bone injury.Conventional radiography is a cheap and affordable method to image injuries caused by fi sh in cities with hospitals with limited resources.In all cases reported in this study, radiography was suffi cient to diagnose the retention of stinger fragments.Surgical removal of these fragments resulted in complete resolution of infl ammation.
Ultrasound can be useful to discard any radiolucent foreign bodies such as cartilage fragments of the fi sh.The sensitivity for detecting foreign bodies, regardless of composition, varies in the literature, with studies reporting up to 94-100%.Ultrasound is the modality of choice for detection of foreign bodies in patients who present a history of perforating wounds ( (7) .In addition, ultrasound allows the diagnosis of fl uid collections and/or muscle-tendon and ligament lesions.The examination should be performed with high-frequency linear transducers that allow the visualization of small fragments of the stinger as linear hyperechoic structures, producing posterior acoustic shadowing (6) (7) .A hypoechoic halo often appears within the fi rst 24 hours due to the local infl ammatory response, aiding in the visualization of the foreign body (6) (7) .
Computed tomography (CT) has limitations regarding the detection of small foreign bodies.However, thin slices acquired by multislice equipment increase its sensibility.Selective preoperative evaluation with CT can provide useful information to the surgeon and can considerably lessen the extent of the surgery (9) (10) (11) .Due to radiation exposure and higher costs, CT should be considered in specifi c cases, such as high clinical suspicion of retained fragments even after negative ultrasound evaluation or in case of chest or abdomen injuries, to evaluate and discard any visceral lesions (7) .Magnetic resonance imaging (MRI) detection of foreign bodies can be diffi cult, especially if the foreign body is small (e.g., a retained fragment of the stinger) and is not associated with complications that MRI can detect based on soft tissue contrast enhancement (9) .Examples of

FIGURE 1 .
FIGURE 1. Marine catfi sh (Top left).Pectoral Sting in detail (Top right).Persisting infl ammation three days after an injury caused by a catfi sh (Bottom left).Conventional radiography of the injured left foot (Bottom right).Increased radiographic density is seen around the fi rst metatarsophalangeal joint (soft-tissue swelling).Note the sharp radiopaque structure near the fi rst metatarsal head (fragment of the stinger).

FIGURE 2 .
FIGURE 2. Radiographic evaluation of a patient with signifi cant infl ammation in the right hallux two days after an injury caused by a catfi sh.The fragment of the stinger is visible next to the fi rst metatarsophalangeal joint, and is surrounded by soft tissue swelling (Left).Radiographic evaluation shows a large stinger fragment that projects into the right foot cuboid bone, resulting in infl ammation (Right).

FIGURE 3 .
FIGURE 3. Conventional radiography of the hand showing embedded portions of the stinger near the fi rst metacarpal bone that project over the second metacarpal bone.The breaking of stingers/barbs led to persisting infl ammation and pain in the hands (Top).The only defi nitive treatment consisted of surgical removal of the fragments, The penetration of the sting is highly traumatic and the break in the wound is always possible.(Bottom).