SAEM Clinical Images Series: When it is Not Just a Knot

knot

A 12-year-old male with a history of hydrocephalus status post ventriculoperitoneal (VP) shunt placement presented with an abdominal “knot.” The patient’s mother noticed the knot two days ago, on the right anterolateral thorax, which has steadily been increasing in size. The patient had no known trauma to the area or had been bitten or stung by any insect. He has otherwise been complaining of a headache, generalized, without positional changes, improved with home acetaminophen, ice pack, and rest. There were otherwise no associated vision changes, nausea, vomiting, mental status changes, or fever.

Additional Images

Physical Exam

Vitals: T-36.2°C; HR 74 bpm; BP 144/75 mm Hg; RR 20; O2 Sat 96% RA

General: Well-appearing teenager in NAD.

HEENT: NC/AT. PERRL approximately 2-3 mm bilaterally. EOMI.

Neck: Supple, no meningismus.

Chest Wall: Induration to the right anterolateral thorax 5 cm x 4 cm without erythema, fluctuance, or drainage, non-tender to palpation.

Neurological: Alert. No focal neurological deficit observed.

Laboratory Data

Normal

Case Question: What is the cause of this patient's knot?

The cause of the knot is subcutaneous cerebrospinal fluid from a shunt malfunction. The ultrasound images show characteristic “cobblestoning,” indicating fluid in the subcutaneous tissue, around a linear hyperechoic object, the catheter of the VP shunt. On the plain film imaging, a disconnect was found between the thoracic and abdominal portions of the VP shunt. Up to 80% of patients with VP shunts will have experienced a shunt malfunction after 12 years, according to one study, with fractured tubing causing shunt failure in around 15% of all cases (1).

Case Question: What are common signs and symptoms of the patient's underlying diagnosis?

Nausea, vomiting, headache, irritability, or decreased mental status are common but nonspecific findings in shunt malfunction. Pediatric patients may present with other signs such as bulging fontanelles, increasing head circumference, or feeding and behavioral changes. An increase in the interval ventricular size can be seen in neuroimaging but can be absent in as many as 20% of patients (2). If there is a high degree of clinical suspicion for shunt malfunction, normal or unchanged neuroimaging should not preclude neurosurgical consultation.

Case Discussion

Take-Home Points

In the United States, mechanical causes of VP shunt malfunction are the most common presentation, such as catheter obstruction, fracture along the clavicle or ribs, degradation of tubing, and migration of the distal catheter due to changes in height or weight.
Rarely, patients can develop an accumulation of CSF at the distal catheter of the VP shunt due to migration into the abdominal wall forming an abdominal pseudocyst.
In patients with VP shunts, abdominal complications should be considered as a sign of shunt malfunction.
Consider pertinent physical exam findings and POCUS to confirm the diagnosis of shunt malfunction at the distal catheter.

References

Sainte-Rose C, Piatt JH, Renier D, Pierre-Kahn A, Hirsch JF, Hoffman HJ, Humphreys RP, Hendrick EB. Mechanical complications in shunts. Pediatr Neurosurg. 1991-1992;17(1):2-9. doi: 10.1159/000120557. PMID: 1811706.
Reynolds RA, Ahluwalia R, Krishnan V, Kelly KA, Lee J, Waldrop RP, Guidry B, Hengartner AC, McCroskey J, Arynchyna A, Staulcup S, Chen H, Hankinson TC, Rocque BG, Shannon CN, Naftel R. Risk factors for unchanged ventricles during pediatric shunt malfunction. J Neurosurg Pediatr. 2021 Sep 24;28(6):703-709. doi: 10.3171/2021.6.PEDS2125. PMID: 34560626.

Copyright

Images and cases from the Society of Academic Emergency Medicine (SAEM) Clinical Images Exhibit at the 2023 SAEM Annual Meeting | Copyrighted by SAEM 2023 – all rights reserved. View other cases from this Clinical Image Series on ALiEM.