Catheter-associated mass

Catheter-associated mass, also known as catheter tip granuloma, is a relatively rare complication related to an intrathecal catheter.

Terminology

Although the term catheter tip granuloma is commonly found in the literature, some favor the more general term catheter-associated mass as they actually consist of a heterogeneous group of pathological entities ¹. Moreover, these masses can arise proximal to the tip of the catheter especially if it is fenestrated ².

Epidemiology

Catheter-associated masses have been reported in 0.04% of patients in the first year after insertion of intrathecal catheters and 1.2% six years after insertion ². Overall, the incidence is thought to be below 3% ³.

Clinical presentation

The most common clinical features are ³:

• neurological deficits
• worsening pain
• increased requirements for pain medication

Symptoms can arise from compression of adjacent structures (spinal cord, thecal sac and nerve roots). As such, the clinical presentation can vary according to the level of the lesion and the structures that are compressed. Cases of spinal stenosis have been reported ³.

Pathology

Histologic examination often reveals central necrosis with a peripheral margin of inflammatory and fibrotic cells derived from the arachnoid with increased vascularity ². Despite being classically described as granulomas, they usually do not meet the histopathologic criteria for true granulomas ².

Apart from actual intrathecal or intraparenchymal granulomas, different etiologies have been described such as epidural fibrosis, drug precipitate (usually bupivacaine), and infectious processes ¹.

Radiographic features

They usually consist of an intradural extramedullary lesion.

CT myelogram

CT myelogram is an adequate alternative if there is a contraindication to MRI. A filling defect is usually seen at the tip of the intrathecal catheter, reflecting the catheter-associated mass.

MRI

The signal on MRI is based on a few case reports. According to the main radiology paper on the subject, it can be ¹:

• T1: variable signal from intermediate to hyperintense
  • a lamellated appearance can be seen
• T2: centrally hyperintense
  • presumably due to necrosis
• T1 C+: peripheral rim enhancement can be seen
  • presumably related to fibrosis/increased vascularity

Treatment and prognosis

Treatment can be non-surgical or surgical. Non-surgical treatment consists of infusion discontinuation; surgical treatment consists of revisiting or removing the catheter and spinal decompression if needed ^1,4.

Differential diagnosis

It is important not to confuse catheter-associated mass with normal artifacts from the metallic tip of the intrathecal catheter ^1,5.

When small and surrounding the catheter, the diagnosis can be straightforward. However, potential differential diagnoses include:

• epidural hematoma ¹
• disc sequestration
• spinal tumor