Multilocular thymic cyst is a relatively rare cyst that exhibits multilocularity. We report the case of a patient in whom a multilocular thymic cyst arose against a background of follicular lymphoid hyperplasia, in which MRI was useful for the diagnosis. The patient was a male in his 60s who had been treated for suspected Sjögren syndrome and associated peripheral nerve disorders. He had been under observation for an anterior mediastinal mass suggesting follicular lymphoid hyperplasia. He presented to our hospital after being flagged for suspicion of a thymic tumor on screening CT.
At his presentation, multiple soft-tissue-density nodules were observed in the anterior mediastinum on CT, and the nodules increased in size over time. MRI with T2WI and short-TI inversion recovery techniques revealed a multilocular cyst. Multiple nodules were also observed, showing signal attenuation on the opposed phase compared to in phase on T1WI. 18F-FDG PET/CT showed FDG uptake with the SUVmax 2.76, and no apparent FDG uptake was detected.
The differential diagnosis considered a multilocular thymic cyst with follicular lymphoid hyperplasia, and the cyst's surgical excision was performed. Histologically, extensive follicular lymphoid hyperplasia was observed in the background thymic tissue, with multilocular cysts lined by squamous or ciliated epithelium. The conclusive diagnosis was thus a multilocular thymic cyst arising against a background of follicular lymphoid hyperplasia. This patient's case demonstrates that MRI with chemical shift imaging is useful for diagnosing follicular lymphoid hyperplasia and multilocular thymic cysts.

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Rectal cancer typically exhibits an intraluminal growth, but some cases show extramural growth and make it difficult to differentiate from other pelvic tumors. A case is extramural growth-type rectal cancer located in the vagina. The patient was 74 years. CT revealed a 12cm pelvic tumor and lymphadenopathy. Gynecological examination showed a tumor throughout the vagina. Cytology suggested squamous cell carcinoma. Cervical cancer was suspected. MRI showed a normal cervix and vaginal tumor with rectal invasion. Vaginal cancer or rectovaginal septum tumor was suspected from the MR images. Histological diagnosis confirmed intestinal-type adenocarcinoma, indicating rectal cancer with vaginal invasion. Re-evaluation of MRI images showed hemorrhagic necrosis in the vaginal tumor, whereas the rectal wall tumor had consistent signals with common rectal cancer, suggesting an original tumor. Determining the primary site of extramural growth-type rectal cancer can be difficult, but MRI-based internal characterization of the tumor can facilitate diagnosis.

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In women of reproductive age with acute abdominal pain, gynecologic or pregnancy-related disorders should be considered. We present a patient's case in which it was difficult to distinguish between ovarian tumor torsion and subserosal uterine leiomyoma torsion. The emergency contrast-enhanced CT findings revealed typical findings of subserosal uterine leiomyoma torsion. The patient was a 29-year-old woman with worsening acute lower abdominal pain who was transferred to our hospital after being suspected of having ovarian tumor torsion or subserosal uterine leiomyoma torsion. Since she had increasing pain and an inflammatory response, laparoscopic surgery was performed the following day. The subserosal uterine leiomyoma torsion was identified on the ventral side of the uterine corpus.
Subserosal uterine leiomyoma torsion is a rare disease that can cause hemorrhagic necrosis, peritonitis, and sepsis, which can be life-threatening. Since ultrasound and MRI are not always useful for diagnosing this disease, it is important to determine whether contrast-enhanced CT scans can reveal findings suggesting subserosal uterine leiomyoma torsion. The following findings facilitate the differentiation of subserosal uterine leiomyoma torsion from other diseases on contrast-enhanced CT: (i) poor contrast enhancement, (ii) thin rim enhancement, and (iii) dark fan sign. In particular, the dark fan sign has high specificity. In the present patient's case, the findings on contrast-enhanced CT were consistent with all of these features.
Normal bilateral ovaries were identified in our patient, and there were no signs of ovarian tumor torsion on the contrast-enhanced CT scan. When normal bilateral ovaries are identified in this manner, ovarian tumor torsion can be ruled out. However, this is often difficult in practice. As this patient's case shows, it is important to evaluate contrast-enhanced CT findings in women of reproductive age with acute abdominal pain when considering subserosal uterine leiomyoma torsion in the differential diagnosis.

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Myositis ossificans, commonly observed in young adults’ extremities following trauma, is a benign heterotopic bone formation. We report a rare case of bilateral psoas muscle myositis ossificans that occurred in a Japanese woman in her 50s after she experienced a lumbar vertebral fracture. She initially presented with fever, elevated inflammatory markers, and psoas muscle swelling, leading to a misdiagnosis of infectious or IgG4-related myositis. Antibiotic treatment was administered. Imaging later revealed calcifications in the psoas muscles, and a CT-guided biopsy confirmed the diagnosis of myositis ossificans. Without further treatment, inflammation did not recur; progressive bone maturation and muscle atrophy developed over 2 years. This case emphasizes the need to consider myositis ossificans in differential diagnoses of post-fracture fever and muscle swelling.

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A 73-year-old Japanese man presented with abdominal pain. Abdominal CT and MRI revealed a tumor in the left lobe of the liver with extrahepatic growth. The tumor had exhibited rapid enlargement over a 7-month period and consisted of mildly enhanced solid components and unenhanced cystic components. Based on the imaging findings a malignant liver tumor with suspected hilar lymph node metastasis was diagnosed. However the histopathological examination revealed that the patient's intrahepatic and extrahepatic tumors were identical with the extrahepatic portion extending into the omental sac and no evidence of lymph node metastasis. The final diagnosis was undifferentiated embryonal sarcoma of the liver.

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