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Intramuscular Cysticercosis

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Intramuscular Cysticercosis Radiology Case
Intramuscular Cysticercosis Radiology Case

Quiz

The definitive host of this parasite is?

  1. Pig
  2. Man
  3. Cattle
  4. Cyclops

Pathophysiology

  • Cysticercosis is a parasitic infection caused by encysted larvae of Taenia solium, the pork tapeworm. Man is the definite and pig is the intermediate host.
  • T. solium infection in a human occurs when the cysts are ingested from undercooked pork. The encysted larval form of T. solium called cysticercus cellulosae, can remain viable in this stage for a long time.
  • Living larvae evade the immune system and do not elicit inflammation and can remain clinically silent. Symptoms occur depending on the location and the size of the lesion. When the larva dies, it induces an acute inflammation resulting in local pain and myalgia.
  • Degeneration of the cyst may result in intermittent leakage of fluid, which causes a chronic inflammatory response, with a collection of fluid around the cyst. The cyst can degenerate and completely calcify.
  • When the muscle burden of the cyst is large, pseudohypertrophy of the muscle results, characterised by multiple nodules.

Key Imaging Features

USGFour different sonographic patterns of intramuscular cysticercosis are

  1. Eccentric echogenic scolex and inflammatory mass around it, as a result of the death of the larva
  2. Irregular cyst with very minimal fluid on one side, indicating leakage of fluid without the scolex due to escape of scolex outside the cyst or due to partial collapse of the cyst
  3. Irregular collection of exudative fluid within the muscle within the scolex due to chronic inflammatory reactions around the cyst
  4. Calcified cyst

MRI

  • The cyst appears hypointense on T1W, hyperintense on T2WI, oval or elliptical directed along the course of muscle fibres
  • Scolices appear intermediate to low signal intensity on T2WI, the intermediate signal on T1WI
  • Post-contrast perilesional enhancement
  • Overlying soft tissue edema
  • GRE- blooming noted in the calcified scolex

CT- Fluid signal intensity cystic lesion, hypodense perilesional edema. Multiple cysts are seen as millet seed-shaped elliptical calcifications in the muscles on radiographs or CT scans, giving a so-called starry-sky appearance.

Imaging Recommendation :

MRI is the modality of choice to detect the stage of the disease and perilesional edema

Top 3 Differential Diagnosis:

  1. Intramuscular abscess– A thick-walled hypoechoic collection with surrounding soft tissue edema with the appropriate clinical feature.
  2. Epidermoid cyst- A Well-defined hypoechoic lesion without significant perilesional edema in non-infected lesion
  3. Neurofibromas- Hyperintense lesion with a central hypointense dot showing heterogeneous enhancement 

The absence of oval/round well-defined cystic lesions with an eccentric echogenic scolex will help in differentiating from cysticercosis.

Clinical Features :

  • Symptoms – Painful, tender swellings commonly seen in the head, neck, trunk and upper extremity than the lower extremity. Three types of clinical presentation in intramuscular cysticercosis are myalgic, mass-like and pseudotumor or abscess-like type. Compressive neuropathy and vascular compromise can occur depending on the size and location of the lesion.
  • Age/Sex predilection– No age or sex predilection
  • Risk factors– History of travel to an endemic zone

Classification System:

Active Stage:

Stage I: Vesicular cysticercosis – Presence of viable cysts containing fluid-filled vesicles.

Stage II: Colloidal cysticercosis – Presence of degenerating cysts with a granular or colloidal appearance.

Inactive Stage:

Stage III: Nodular cysticercosis – Presence of calcified cysts forming small nodules within the muscle tissue.

Stage IV: Calcified cysticercosis – Presence of fully calcified cysts, no longer viable.

Etymology and synonyms:

Cysticercosis is derived from the combination of two words: “cystic” and “cercosis.”

“Cystic” refers to the formation of cysts, which are sac-like structures filled with fluid or semi-solid material.

“Cercosis” is derived from the Greek word “kirkos,” meaning “a ring” or “a circle.” It is used to describe a condition caused by the presence of parasites belonging to the genus “Cysticercus.”

Therefore, when combined, the term “cysticercosis” refers to a condition characterized by the development of cysts caused by the presence of the larvae of a tapeworm known as Taenia solium.

Treatment:

  1. No treatment in asymptomatic lesions
  2. Medical treatment with praziquantel and albendazole- depending on the site and number of the lesions
  3. Surgery- lesion causing neurovascular compromise

References:

Single best review article:

 Case co-authored by TeamGyan Member Dr Mansi

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