Soft Tissue Ultrasound • Cysticercosis

Eccentric Echogenic Mural Nodule (Scolex)

Characteristic Ultrasound Finding of Soft Tissue Cysticercosis

Chest Wall Ultrasound Soft Tissue Sonography Updated 2026 Educational Reference

Definition → An eccentric echogenic mural nodule (scolex) is a small bright nodule attached to the wall of a cystic lesion and represents the head (scolex) of the larval Taenia solium parasite.

It is the most characteristic and diagnostic ultrasound feature of cysticercosis.

Ultrasound Appearance → Ultrasound typically demonstrates a well-defined anechoic or hypoechoic cyst containing a small eccentric echogenic mural nodule. The nodule is usually attached to the inner wall of the cyst rather than floating freely within it. This appearance is commonly described as the "cyst with dot sign". The bright echogenic dot corresponds to the invaginated scolex of the parasite.

Why is it Important? → Identification of a scolex is considered pathognomonic for cysticercosis. When a cyst containing an eccentric echogenic mural nodule is visualized, the diagnosis can often be established confidently without additional invasive investigations. Recognition of this finding helps differentiate cysticercosis from abscesses, epidermoid cysts, hematomas, lymph nodes, and soft tissue tumors.

Associated Findings → Depending on the stage of the disease, surrounding inflammatory edema, hypoechoic soft tissue swelling, and mild peripheral vascularity may be present. Degenerating cysticerci may show irregular cyst walls, internal debris, partial collapse of the cyst, or surrounding inflammatory reaction. Chronic lesions may eventually calcify and appear as echogenic foci with posterior acoustic shadowing.

Key Sonographic Sign → Cyst + Eccentric Echogenic Dot = Scolex
Scolex Visible = Diagnostic of Cysticercosis
The visualization of an eccentric echogenic mural nodule within a cystic lesion is one of the most classic and frequently tested ultrasound signs in soft tissue sonography.

---

ECCENTRIC ECHOGENIC MURAL NODULE (SCOLEX)

✎ Soft Tissue Ultrasound • Cysticercosis • MCQ Practice

Quick study → An eccentric echogenic mural nodule (scolex) within a cystic lesion is the classic ultrasound appearance of cysticercosis. The scolex represents the head of the larval Taenia solium parasite and is considered a pathognomonic sign.

01. The eccentric echogenic mural nodule seen in cysticercosis represents:

A. Calcification B. Abscess debris C. Scolex (head of larval tapeworm) D. Hemorrhage

02. The presence of a scolex within a cyst is considered:

A. Nonspecific finding B. Pathognomonic for cysticercosis C. Sign of abscess D. Sign of malignancy

03. Cysticercosis is caused by the larval stage of:

A. Ascaris lumbricoides B. Echinococcus granulosus C. Taenia solium D. Enterobius vermicularis

04. The classic sonographic appearance of cysticercosis is:

A. Thick-walled abscess B. Solid vascular mass C. Cyst with an eccentric echogenic dot D. Calcified lymph node

05. The term "mural nodule" means:

A. Nodule within vessel B. Nodule attached to the wall of a lesion C. Floating nodule D. Calcified nodule

06. The scolex is usually located:

A. Centrally within the cyst B. Outside the cyst C. Eccentrically along the cyst wall D. Within adjacent muscle

07. Color Doppler examination of a viable cysticercus usually demonstrates:

A. Marked internal vascularity B. Arterial aneurysm C. Absent internal vascularity D. Venous thrombosis

08. Which ultrasound sign is most characteristic of soft tissue cysticercosis?

A. Ring-down artifact B. Cyst with scolex sign C. Comet-tail artifact D. Snowstorm appearance

09. Which of the following is a common differential diagnosis of cysticercosis?

A. Epidermoid cyst B. Abscess C. Soft tissue tumor D. All of the above

10. Which statement regarding a scolex is TRUE?

A. It represents the larval head of Taenia solium B. It represents a calcified vessel C. It is a malignant feature D. It is found only in liver lesions

✎ REMEMBER

Scolex = Head of Taenia solium larva
Cyst + Eccentric Echogenic Dot = Cysticercosis
Scolex Visible = Pathognomonic Sign
Usually seen as a cyst containing an eccentric mural nodule with absent internal vascularity.