What are the surgical properties of Dysembryoplastic Neuroepithelial Tumors (DNETs)?

Surgical Properties of Dysembryoplastic Neuroepithelial Tumors (DNETs)

Complete surgical excision of the DNET together with a rim of surrounding dysplastic brain is the optimal surgical approach, as this extended resection strategy provides superior seizure control with low morbidity compared to lesionectomy alone. 1

Key Surgical Characteristics

Anatomical Features

• DNETs are superficial intracortical lesions with multinodular architecture, most commonly located in the temporal lobes (62%), followed by frontal lobes (31%), and parietal/occipital lobes (7%) 2, 1
• Satellite nodules are frequently present on the medial side of the main mass, and these separate nodules are bona fide tumor components that can grow during follow-up 3
• The tumors often involve or are in close proximity to mesial temporal structures in approximately 73% of temporal lobe cases 4

Critical Surgical Considerations

Associated cortical dysplasia (CD) is present in 52-83% of cases adjacent to DNETs, and this surrounding dysplastic cortex is the primary source of ongoing seizure activity 5, 1. This high frequency of associated CD fundamentally changes the surgical approach:

• Resection of the DNET alone (simple lesionectomy) leads to significantly higher seizure recurrence rates 1
• In one series, 39% of DNET + CD patients who underwent incomplete resection required repeat surgery for recurrent seizures, while none of the patients without CD required reoperation 1
• Extended resection including the dysplastic cortex achieves seizure freedom in nearly all patients (100% in one prospective series of 24 patients with long-term follow-up) 1

Optimal Surgical Strategy

The evidence strongly supports a two-tiered approach:

1. Complete excision of the entire DNET including all satellite nodules 3
2. Extended resection to include the rim of surrounding dysplastic brain where epileptogenicity may or may not have been confirmed preoperatively 1

Temporal lobectomy provides better seizure outcomes than lesionectomy alone when DNETs are located in the temporal lobe 1. In one study, 11 of 13 patients who underwent extended lesionectomy coupled with neuronavigation remained seizure-free for 2-11 years postoperatively 6.

What NOT to Do

Stereotactic biopsy alone is contraindicated because it may generate an unrepresentative tissue sample consisting only of the oligodendroglial component, leading to misdiagnosis 1

Incomplete resection dramatically increases the risk of seizure recurrence, particularly when dysplastic cortex is left behind 1, 3. Two patients (11.1%) in one series required repeat operations, and both had undergone incomplete initial lesionectomy 1

Surgical Goals and Outcomes

The primary therapeutic goal is complete seizure control without anticonvulsants, with avoidance of malignant transformation as the secondary goal 1, 5

Expected Outcomes

• Complete resection achieves excellent long-term seizure control with 12 of 14 patients (86%) becoming seizure-free or having >80% reduction in seizure frequency 4
• Recurrence after complete surgical resection has not been described in the literature 5
• DNETs remain clinically stable over many years with stable disease on serial imaging over a mean of 4.5 years 1, 5
• The duration of epilepsy prior to resection does not affect epilepsy outcome 5

Tumor Behavior

• Malignant transformation is extremely rare and poorly documented, with the few reported cases confounded by prior radiation therapy or diagnostic uncertainty 1
• Long-term follow-up (mean 9 years in the original series of 39 patients) showed neither clinical nor radiological evidence of recurrence in any patient, even when tumor removal was considered incomplete or subtotal in 44% of cases 2

Practical Surgical Pearls

Use of MRI-based intraoperative neuronavigation is recommended to ensure complete removal of all tumor nodules and surrounding dysplastic cortex 6

Visual inspection for dysplastic cortex during surgery is helpful to ensure that the extended lesionectomy includes any visibly dysplastic cortex 1

Concordance between multiple diagnostic modalities (MRI, EEG, PET, SPECT) is associated with better surgical outcomes, helping to define the extent of resection needed 5, 7