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| Discussion |
Case Report: A 64-year-old man, hailing from Uttar Pradesh, presented with fever and acute abdominal pain radiating to the right groin. Epigastric discomfort and dyspepsia were also present. Occupational history was non-significant. On examination, the abdomen was soft. Bilateral inguinal adenopathy was found. He had no scrotal abnormalities. His symptoms improved on empiric antibiotic therapy.
Plain and contrast enhanced CT scans of the chest and abdomen were performed.
There was a low-density tubular structure in the posterior mediastinum adjacent to the gastro-esophageal junction and to the right of the aorta. It extended from the mid thoracic level to the level below the diaphragmatic crura.
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Fig: 1 |
CT scan abdomen plain and contrast enhanced was performed. It revealed a cystic lesion with thin wall in relation to the GE junction and the retrocardiac esophagus.
Multiple small dilated hypodense non enhanching channels were seen in the retro-peritoneum, which started at the level of renal hilum, and were traced upto the spermatic cord on both sides. Central attenuation value of these diffusely distributed channels ranged from 8 to 27 HU in retroperitoneum and from 22 to 30 HU along common iliac and external iliac vessels. Stomach was grossly distended, however no obvious mass lesion was seen in pylorus or duodenum. No adenopathy, pleural effusion or ascites was noted.
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Fig: 2 |
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Single-shot fast spin-echo MR images in multiple planes confirmed a fluid-filled tubular structure extending from mid thoracic level cranially to the level of the spermatic cords caudally consistent with a distended thoracic duct and dilated tortuous lymphatics. No chylothorax was present.
MR images confirmed nonenhancing fluid-filled structures distributed in the retroperitoneum and pelvis consistent with diffuse lymphangiectasia. More readily apparent on MRI were superficial inguinal lymphangiectasia and mild scrotal subcutaneous lymphangiectasia. Multiple tortous channels hyperintense on T2W and hypointense on T1W images in retroperitoneum extending from level of spermatic cords upto level of mid cisterna chylii in thorax.
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Fig. 8
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Fig. 10 |
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The patient underwent blood tests which revealed eosinophilia.
High-power microscopic view of microfilaria of Wuchereria bancrofti was obtained from peripheral blood smear and showed presence of distinct sheath and absence of nuclei in tail (Wright-Giemsa stain).
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Fig: 11 |
DIAGNOSIS:
Retroperitoneal Filariasis. With dilated collateral lymphatic ducts.
DISCUSSION:
Human lymphatic filariasis is caused by infections with W. bancrofti, Brugia malayi, or Brugia timori. These parasites are found in many tropical and subtropical areas of the world. The adult worms live in the lymphatics throughout the body and cause extensive lymphangiectasia by obstructing lymph flow. Filariasis is the most common cause of acquired lymphedema in the world. Interestingly, our patient had neither scrotal nor lower extremity edema.
Lower chest CT revealed a tubular structure in the posterior mediastinum, coursing along the thoracic spine. Its central attenuation value ranged from 15 H in a more distended segment to 32 H in the least distended portion, which was behind the left atrium. The low-density tubular structure in the posterior mediastinum of this patient is a distended thoracic duct. The thoracic duct collects lymph from most body tissues and transmits it back into the blood stream. The duct originates in the abdomen anterior to the second lumbar vertebra at the cisterna chyli and then ascends into the thorax through the aortic hiatus of the diaphragm slightly to the right of the midline. Within the posterior mediastinum of the thorax and still coursing just ventral to the vertebral column, the thoracic duct gradually crosses the midline to the left. The duct then ascends into the root of the neck on the left side and drains into the left subclavian vein near the junction of the left internal jugular vein.
Abdominal CT scan revealed low-attenuation channels distributed in the retroperitoneum and pelvis that showed no enhancement with IV contrast material. The central attenuation value ranged from 8 to 27 HU in the retroperitoneum and 22 to 30 HU in the pelvis along the iliac vessels. No discrete mass was identified associated with this diffuse abnormality. MR images clearly revealed nonenhancing confluence of prominent lymphatic ducts and vessels. Superficial inguinal lymphangiectasia and mild scrotal subcutaneous lymphangiectasia were also more readily evident on heavily T2-weighted images.
Case et al. used MRI to detect dilated lymphatic vessels in ferrets infected with B. malayi. In 1999, Blacksin et al. reported the first description of MRI findings in a human, a case of bancroftian filariasis affecting the ankle joint .Witte et al. described the potential use of MRI, particularly fat-saturated T2-weighted images, for the evaluation of the lymphatic system. Schick et al. described cystic lymph node enlargement of the neck on MRI in a patient with filariasis.
This case shows the distended thoracic duct on CT as a nonenhancing low-attenuation tubular structure in the posterior mediastinum. Its recognition is made easier by knowing the anatomic origin and course of the thoracic duct. Diffuse lymphangiectasia in the retroperitoneum and pelvis appears on CT as nonenhancing low-attenuation channels along major vessels and is not associated with a discrete mass. MR images, particularly single-shot fast spin-echo images, a heavily T2-weighted pulse sequence, helped reveal the nonenhancing fluid-filled thoracic duct and prominent lymphatic ducts and vessels.