Discussion
Among AML subtypes, M3 is usually considered highly curable5; however, treatment introduces new complications to the scene, mainly because of the induction of immunosuppression. Opportunistic Infections and particularly fungal infections such as candidiasis are one of these complications. It is well known that an increase in the fungal load, a compromised mucosal surface, and a lowered host immune response are all necessary for the disease to manifest. Other risk factors can also contribute to this process, namely the presence of indwelling catheters and recent surgical and percutaneous interventions 3. Candida species originating from intestinal microbial flora typically spread through blood circulation and cause macro nodular skin lesions. Organisms may spread to other organs, especially the liver, spleen, and kidneys6.
Ultrasonography remains a useful tool for detecting and monitoring candidiasis lesions; however, candidal lesions may be undetectable in imaging before neutrophil count recovery, especially in chronic disseminated candidiasis (CDC). Manifestations of imaging depend on the stage of the disease, but the most frequent ultrasound pattern in the liver and spleen is several small hypoechoic lesions. Four dominant patterns of hepatosplenic involvement have been described. The earliest pattern is composed of a peripheral hypoechoic zone that correlates with fibrosis, with a second hyperechoic zone composed of inflammatory cells. The central hypoechoic nidus relates to necrotic fungal elements. This pattern is called ”wheel within a wheel.” The second pattern is called ”bull’s eye,” or target pattern, with a peripheral hypoechoic halo encircling a central echogenic core. The third and most common pattern is seen as multiple hypoechoic lesions that can be seen in conjunction with the other three patterns. The fourth pattern, manifesting as echogenic foci, usually is seen at the late stages of the disease and correlates microscopically with central fibrosis or calcifications, or both 7.
MRI seems to be superior to computed tomography(CT) scan and ultrasonography in identifying hepatosplenic and musculoskeletal lesions associated with candidiasis. In a patient with acute hepatosplenic or soft tissue candidiasis, lesions on MRI are round, measured <1 cm in diameter, markedly hyper-intense on T2-weighted images and show restriction on diffusion-weighted imaging(DWI). At the chronic stage, especially with antifungal treatment, a hypo-signal rim surrounding the primary lesions and a non-enhancing center on contrast images are seen, which is consistent with the necrotic core seen on histologic examination. When the lesions are calcified, they appear hyperdense on CT scan and low signal on MRI 8-10.
There aren’t many studies that provide imaging results of subcutaneous and intramuscular candidal abscesses. We discovered a few case reports in the literature that contained imaging data such as CT or MRI (Table. 1). When dealing with an AML patient who has various cutaneous, muscular, and hepatosplenic lesions, we must evaluate a variety of differential diagnoses, including chloroma, multifocal bacterial abscess, tuberculoma, cysticercosis, and hydatidosis, in addition to systemic candidiasis.
Chloromas or myeloid sarcomas are comprised of immature myeloid cells, most often leukemic blasts11. It is characterized by an extramedullary tumoral lesion which can readily be diagnosed by ultrasonography or CT scan and biopsy 12. The numbers of these lesions are lower than candidal lesions usually. MRI presents it as iso to hypo-signal on T1 and mildly hyper-signal on T2 weighted images. They have vascularity in Doppler ultrasound and show enhancement after contrast injection in CT scan and MRI 13. Bone and periosteum is the most common site of involvement, but any tissue can be affected, such as skin, orbit, paranasal sinuses, and central nervous system 14, 15. Moreover, chloroma is more prevalent in AML M2, M4, and M5 subtypes, not M3 16.
Multifocal bacterial abscesses can occur in immunocompromised patients. Septic emboli can be primarily found in the lungs, especially in AML patients with port-catheter 17. However, culture and gram staining of blood and aspirated fluid of abscess returned negative for our patient; his chest x-ray was also normal. Moreover, Bacterial abscesses don’t show the typical ”bull’s eye” ultrasound pattern mentioned before.
Extra-pulmonary tuberculosis should always be considered as a differential diagnosis of multiple subcutaneous and hepatosplenic masses in an immunocompromised patient, even though it’s a rare finding18. These abscesses are often observed in the chest wall and spine. The limb is a very uncommon location of involvement19. They are often secondary to ruptured necrotic lymph nodes, tuberculous osteomyelitis, or arthritis20. Culture and Acid-fast staining of blood and aspirated fluid of abscess were also negative.
Cysticercosis is a kind of endemic parasitic disease that is a very rare entity in our country. The central nervous system and skeletal muscles are humans’ most commonly affected tissues. In ultrasonography, the scolex is seen inside the lesion, which may be calcified. When the lesions are cystic, they have similar characteristics to fluid on both CT and MRI, but when these lesions calcify, they appear as hyperdense foci parallel to muscle fibers on CT, giving a characteristic appearance called ”rice-grain” calcification 21. This disease is not related to the host’s immunity state 22.
Soft tissue and skeletal muscle hydatid cyst is a very rare condition and is usually secondary. They can occur in the lower extremities, trunk, neck, or legs. Pectoralis major, Sartorius, quadriceps, and gluteus muscles can be involved. It usually appears as a focal multi-vesicular cystic lesion in the muscle(s) that can invade the adjacent bone 23. They have a characteristic appearance on ultrasound, CT scan, and T2 weighted sequence of MRI as a cystic lesion with serpentine undulant membranes called ”water lily sign” or ”serpentine sign” in the liver, spleen, and other regions24.
Soft tissue mycetoma due to maduramycosis or other fungal infections usually occurs in the foot and in endemic areas. Mycetoma is a kind of chronic inflammation of soft tissue caused by fungi or actinomycetes. They appear as multiple, small, round T2 hyperintense lesions with central hypointense foci in MRI. Central hypointense foci are mycetoma grains in pathology called ”dot in a circle sign,” which is specific for this entity 25, 26. One of our patient’s lesions had a similar appearance in MRI (Figure 2C). Although the ”dot in a circle” sign is a characteristic sign of mycetoma, the accumulation of candida hyphae can cause hypointense signal areas in both T2 and T1 weighted images in MRI 27.