Case History:
This was a case of 32-year-old male, present with a dull pain in upper abdomen. Computed tomography revealed a multiple solid cystic masses in the liver. Clear fluidic material was aspirated through ultrasound guided fine needle aspiration cytology (FNAC).
Cytopathology:
- Brood capsules along with protoscolices are seen {These appear as round dense eosinophilic structures with many bluish-purple semi-translucent eggs like bodies (nucleated cells) along with scolices and hooklets inside}
- Few inflammatory cells and necrotic debris are seen in the background.
- Higher magnification reveals protoscolices with many hooklets.
- Isolated refractile hooklets (circle mark) are present with adjacent sheet of benign hepatocytes.
- Part of laminated membrane appears as pinkish strips on hematoxylin-eosin stain.
Practical Points of Pathoclinics:
- The hydatid cyst is a serious helminthic disease of human, caused by an infestation with larval tapeworms of the genus Echinococcus. Echinococcus granulosus and Echinococcus multilocularis are the most common. The disease has a worldwide distribution. The most common site is liver; followed by lung. Hydatid cyst can be seen in brain, cavernous sinus, submandibular gland, thyroid gland, heart, pleura, chest wall, kidney, spleen, pancreas, peritoneal cavity, inguinal canal, breast, bone and soft tissue.
- Hydatid cyst is usually a very slow growing cystic lesion so, diagnosis is usually delayed for months to years after the initial infection with Echinococcus in most of the cases. Patients are usually presenting with abdominal pain, hepatomegaly, portal hypertension (due to portal vein compression) and obstructive jaundice (due to bile duct compression). Acute presentation may occur due to bacterial infection, cholangitis and cyst rupture in peritoneal or pleural cavity, especially in untreated patient with large cystic lesions. Clinically hydatid cyst may be confused with benign or inflammatory liver lesions like abscess, hemangioma, solitary bile duct cyst and hepatobiliary cystadenoma.
- Ultrasound and computed tomography scan have good diagnostic accuracy especially in predominately cystic lesion of Hydatid. However, in presence of solid component, possibility of variety of benign/inflammatory liver lesions fall in the differential diagnosis.
- Fine needle aspiration cytology (FNAC) is helpful in the early, rapid and reliable diagnosis of hydatid cyst in any location, with no or minimal procedure induced complication. Also, preoperative cytologic diagnosis of hydatid cyst helps to initiate anti-anaphylactic measures before definitive surgery and extra precautions, which are necessary to prevent the accidental rupture of cyst during surgical removal of the hydatid cyst.
- Echography and echinococcus immunologic tests are not confirmatory for preoperative diagnosis.
- The possibility of hydatid cyst should be kept in mind during the FNAC of any cystic lesion of liver. The cytologic diagnosis of hydatid cyst is usually rendered with high accuracy in presence of scolices and hooklets, with/without laminated cyst wall membrane and brood capsules in a variable amount of inflammatory/necrotic background. Presence of laminated cyst wall membrane alone in absence of scolices and hooklets, in the inflammatory background, also favors hydatid cyst in an appropriate clinical context. Long standing lesion may show degenerative changes, calcified brood capsules and hyalinized laminated membrane.
- FNAC complications are almost nil or very minimal, and restricted to urticaria and mild anaphylaxis, which can be treated with anti-anaphylactics medication.
- Grossly, hydatid cyst appears as a white, spherical cystic structure, filled with clear fluidic material. Multiple variable size cysts, ranging from a few millimeters to many centimeters in diameter, are common. Larger cyst contain the multiple daughter cysts. The right lobe of liver involvement is more common. However, multiple cystic lesion can involve all parts of the liver including other abdominal structures .
- Histologically, hydatid cyst has three layers: 1. Outer layer: Paucicellular fibrous layer with few inflammatory cells (outer pericyst). Occasional calcifications can be seen. 2. Middle layer: Thin (1 mm thickness) acellular hyalinized, laminated membrane, appear amphophilic on hematoxylin and eosin stain. 3. Inner layer/germinal layer: 10 to 25 μm in thickness and lined by nucleated cells. Brood capsules along with their protoscolices develop from these nucleated cells. Ovoid protoscolices contain hooklets and sucker. Daughter cysts are structurally similar to primary cyst. Sometimes old fibrotic, degenerated and ruptured cysts may show fibro-inflammatory cells, rich in eosinophils along with calcified debris and only occasional hooklets. Hooklets can be stained with acid-fast stain (Ziehl-Neelsen stain) and Gomori methenamine silver (GMS) stain. Hooklets are birefringent and polarization also highlights the hooklets. However, hematoxylin and eosin stain is sufficient for highlighting the characteristic scolices, hooklets and laminated membrane.
- Surgical excision of the intact hydatid cyst followed by chemotherapy with benzonidazole is the standard treatment, to reduce the chance of seeding, anaphylaxis, and recurrence of hydatid cyst.
Refernces:
Kim AR, Park SJ, Gu MJ, Choi JH, Kim HJ. Fine needle aspiration cytology of hepatic hydatid cyst: a case study. Korean J Pathol. 2013 Aug;47(4):395-8. doi: 10.4132/KoreanJPathol.2013.47.4.395. Epub 2013 Aug 26. PMID: 24009638; PMCID: PMC3759642.
